Bovine Respiratory Disease

July 29, 2019

Management of Highly Stressed, Newly Received Feedlot Cattle

Octavoscene Livestock Diseases, Management Bovine Respiratory Disease, Cattle, Management, Morbidity, Nutrition

Abstract

Morbidity and mortality from bovine respiratory disease (BRD) and associated losses in performance and carcass merit continue to plague the beef cattle industry. Several viral/bacterial agents are responsible for BRD, and interactions occur among the agents. Viral agents often predispose animals to bacterial infections, and Mannheimia haemolytica is the most frequently isolated organism in cattle with BRD.

Laboratory tests are available to characterize organisms causing BRD using easily obtained nasal swab samples. Testing for persistent infection with bovine viral diarrhea virus can be done by a 2-stage technique using PCR and immuno histo-chemistry. Preconditioning programs that include pre-weaning viral vaccination programs along with castration could have a significant influence on decreasing BRD in the cattle feeding industry. Meta-phylactic antibiotic programs continue to be effective; however, antibiotic resistance is a public concern, and additional management options (e.g., direct-fed microbials or other compounds with antimicrobial properties) deserve attention.

Diets with an increased energy concentration achieved by decreasing the dietary roughage concentration may slightly increase the rate of BRD morbidity; however, these diets also increase ADG, DMI, and G:F compared with lower-energy, greater-roughage diets. The extent to which performance and BRD morbidity are affected by dietary protein concentration needs further study, but low and high protein concentrations should probably be avoided. Several trace minerals (e.g., Cu, Se, and Zn) affect immune function, but the effects of supplementation on performance and immune function in model challenge systems and in field studies are equivocal.

Adding vitamin E to receiving diets at pharmacological levels (e.g., >1,000 IU x animal(-1) x day(-1)) seems beneficial for decreasing BRD morbidity, but it has little effect on performance.

Given the limited ability to consistently modify immune function and BRD morbidity through dietary manipulations, we recommend that the diets for newly received cattle be formulated to adjust nutrient concentrations for low feed intake and to provide optimal performance during the receiving period.

INTRODUCTION

Morbidity and mortality from bovine respiratory disease (BRD) in newly weaned/received cattle continue to be the most significant health problems facing the US beef cattle industry. In a recent survey of Kansas
feedlots, there seemed to be a trend for increased death losses in feedlot cattle over the last decade (Babcock et al., 2006), and BRD was the leading cause of morbidity and mortality in a cross sectional survey sent to 561 feedlots in 21 states (Woolums et al., 2005). Mortality from BRD and the expense of medicine and labor to treat BRD contribute to its negative economic and animal welfare costs, but feedlot performance and carcass merit also are affected negatively by BRD (Gardner et al., 1999), magnifying its economic consequences.

Montgomery et al. (1984) reported that BRD negatively affected marbling scores in 3 trials, and quality grade was significantly decreased in 2 of the 3 trials.

Likewise, Roeber et al. (2001) reported lower HCW, marbling scores, and yield grades for cattle treated more than once for BRD compared with untreated cattle, and carcass grades were further decreased in cattle treated for BRD 2 or more times. Calves treated for BRD once returned $40.64 less, those receiving 2 medical treatments returned $58.35 less, and those receiving 3 or more treatments returned $291.93 less than calves that were not treated (Fulton et al., 2002).

Figure 1. Pre- and postweaning factors affecting bovine respiratory disease (BRD) in beef cattle and the resulting outcomes of the disease. + = decreased incidence or consequence; − = increased incidence or consequence; ? = effects not fully understood based on the available data. BVD = bovine viral diarrhea virus.

Although BRD is ultimately a viral/bacterial disease, it is a multifaceted problem with numerous potential exacerbating factors and outcomes (Figure 1).

Stresses due to weaning, marketing, and transportation, previous plane of nutrition, genetics, and health history interact with exposure to viral and bacterial agents. Stress negatively affects the immune system (Blecha et al., 1984) at a time when the animal is more likely to be exposed to infectious agents as a result of commingling. Feed intake by stressed calves is low (Galyean and Hubbert, 1995; Cole, 1996), and low nutrient intake likely augments the negative effects of stress on immune function.

Along with our colleague Louis Perino, we previously reviewed the interaction of nutrition with beef cattle health and immunity (Galyean et al., 1999). Our objective in the present paper is to update topics covered in our 1999 review, to add additional information on strategies to prevent or treat BRD, and to provide suggestions for future research.

CAUSATIVE AGENTS FOR BRD

Although it is important that some discussion on the causes of BRD be included in this review, describing all of the potential causes and interactions associated with BRD is beyond the scope of this manuscript.

Pasteurella multocida, and Histophilus somni (formerly Haemophilus sommus) are of primary concern, with BRD is beyond the scope of this manuscript. Of the bacterial species, Pasteurella (Mannheimia) haemolytica, Mannheimia haemolytica serotype 1 being respiratory the organism most commonly associated with BRD (Pandher et al., 1998).

In addition, viral agents, including infectious bovine rhinotraceitis (IBR), parainfluenza-3 (PI3), bovina viral diarrhea virus (BVDV), bovine syncytial virus (BRSV), and bovine enteric corona virus have been associated with respiratory tract disease in feedlot calves (Plummer et al., 2004). Bovine adeno virus serotype 7 infections have been found in commingled calves and may be more common in calves with concurrent infections with other viruses (Fent et al., 2002). In Europe, Mycoplasma bovis is responsible for at least 25 to 33% of all pneumonia cases in calves suffering from BRD (Gevaert, 2006).

Much recent attention has focused on BVDV. These viruses are classified into 2 genotypes (type 1 and type 2; Ridpath et al., 1994) based on sequences from the 5′ untranslated region of the viral genome and are further characterized into sub-genotypes (1a and 1b, Pellerin et al., 1994; and 2a and 2b, Flores et al., 2002).

Within the 2 genotypes, a further division into cytopathic and non-cytopathic strains is made based on the presence or absence of effects in vitro. Regardless of the biotype or genotype, significant losses can occur.

In cattle with a history of BRD, BVDV non-cytophathic biotypes were isolated more often than cytopathic biotypes, and BVDV1 non-cytopathic biotypes were isolated more frequently than BVDV2 genotypes (Fulton
et al., 2000b). Moreover, BVDV1 genotypes were isolated more frequently than type 2 genotypes from necropsy of calves with fibrinous pneumonia.

An almost equal distribution of BVDV1a and 1b isolates was noted from cattle with a history of BRD, but more BVDV1b than 1a was isolated in necropsy cases of cattle that died from pneumonia (Fulton et al., 2003). Of the US licensed and marketed BVDV vaccines, only one contains BVDV1b strains (Fulton et al., 2003), and although vaccines with BVDV1a and 2a are routinely administered to cattle entering feedlots, most vaccines may not provide adequate protection against BVDV1b (Fulton et al., 2006).

Thurmond (2005) described factors associated with the mode of transmission of BVDV. Transmission of BVD can be vertical (fetal

infection) or horizontal (postnatal transmission). When an infection with a nonpathogenic strain occurs before d 42 to 125 in utero, calves can become persistently infected (PI; McClurkin et al., 1984). Persistent infections are lifelong, and because PI animals constantly shed the virus, this can be an important means of transmission.

Bovine viral diarrhea virus infections often occur in combination with infections by other viruses associated with BRD, particularly PI3 and BRSV (Fulton et al., 2000a). Early in the marketing process, highly susceptible calves are likely at risk to infections by IBR, BVDV types 1 and 2, and BRSV (Fulton et al., 2000a). Although much of the recent research conducted with viral vaccines has focused on BVD, bovine herpes virus 1 (BHV-1, commonly known as IBR) may predispose cattle to pneumonic pasteurellosis (Patel, 2005). Prevention of predisposing viral infections via pre-conditioning programs that include vaccination for viral and bacterial agents known to cause BRD should decrease the incidence of the disease.

DIAGNOSIS OF BOVINE RESPIRATORY DISEASE

Classical Methods

It is generally accepted that a variable but relatively high percentage of animals will succumb to BRD; thus, accurate diagnosis is critical in practical situations.

Most animals are removed for examination and treatment for BRD on or before d 27 of the receiving period (Buhman et al., 2000). Traditional methods for detecting morbid cattle include visual appraisal once or twice daily, with animals displaying various signs including nasal or ocular discharge, depression, lethargy, emaciated body condition, labored breathing, or any combination of these, being removed from pens for further evaluation. Symptomatic animals with a rectal temperature ≥39.7°C are usually considered morbid and given therapeutic treatment.

Perino and Apley (1998) defined a clinical scoring system of: 0 = normal animal; 1 = noticeable depression without apparent signs of weakness; 2 = marked depression with moderate signs of weakness without a significantly altered gait; 3 = severe depression with signs of weakness such as a significantly altered gait; and 4 = moribund and unable to rise. According to their protocol, animals with a rectal temperature of ≥40°C and a clinical score of ≥1 should receive therapeutic treatment.

Given the subjective nature of such protocols, identification of animals with BRD is not always accurate.

Pulmonary lesions indicative of BRD were present at slaughter in 68% of steers that were not treated for BRD, whereas lesions were present in 78% of treated steers (Wittum et al., 1996a). Similarly, in South African feedlots, Thompson et al. (2006) reported that 42.8% of all animals had lung lesions at slaughter, and of the animals with lung lesions at slaughter, 69.5% had never been treated for BRD. We previously suggested (Galyean et al., 1999) that a valuable tool for monitoring BRD diagnosis and treatment would be evaluation of lung lesions at slaughter. Bryant et al. (1999) provided a method for recording pulmonary lesions at slaughter; however, implementation in commercial settings is not common, and few published research studies have scored pulmonary lesions as an indicator of treatment or diagnosis of BRD. Failure to detect morbid animals using current protocols for diagnosis may be related to predator/prey behavior (Noffsinger and Locatelli, 2004), in that if the animals perceive the personnel handling the animals as predators, they will mask the signs of weakness (e.g., depression, illness, lameness, etc.). Therefore, development and implementation of quantitative measures to detect BRD is critical, and several possible candidates will be discussed in the subsequent sections.

Laboratory Tests for BRD and Body Temperature Measurements

Laboratory tests are often used to verify BRD; however, the optimal metabolite, compound, or organism to measure remains to be determined. Any laboratory procedure requires time to complete, which limits its

value. Chute-side tests would be highly desirable; however, such tests are not widely available, are potentially cost-prohibitive, and little data are available to evaluate their efficacy.

Establishing the causative agents of BRD aids proper treatment. DeRosa et al. (2000) reported that nasal swab cultures contained the same bacterial species as transtracheal swab cultures 96% of the time, and nasal swab cultures were genetically identical with the organism causing disease within the lung for 70% of the calves tested. Furthermore, antibiotic susceptibility was generally similar between paired isolates for various antibiotics used to treat BRD.

Thus, a nasal swab culture, which is easy to obtain and process, should be useful for identifying the species responsible for causing bacterial pneumonia and also should be indicative of antibiotic susceptibility (De-Rosa et al., 2000).

Immunohistochemistry (IHC) is frequently used to detect BVDV antigen in skin biopsies. Other methods microplate virus isolation, and reverse-transcriptase PCR (RT-PCR) assays (Dubovi, 1996). Viral isolations from blood leukocytes or serum also can be used to identify PI BVDV animals. The time to complete these tests varies among laboratories, but the process can take approximately 10 d. In addition to assay costs, costs associated with sample collection, animal handling, sample shipment, etc. can be significant, and it is likely cost-prohibitive to sample all calves received in a given lot. The IHC test seems reliable, and calves recently vaccinated with modified live vaccines have not caused false positives (DuBois et al., 2000); however, skin biopsy samples cannot be pooled, thereby increasing costs. Larson et al. (2005) suggested using RT-PCR on pooled blood samples (30 animals), followed by an IHC test only on animals represented in the pooled samples that returned positive assay results. This 2-test strategy might be cost effective, but it would increase the lag time in detecting PI BVDV calves and increase the time they would be commingled with other cattle.

During the initial tissue insult of the disease, a set of reactions result in the release of soluble mediators termed the acute-phase response (Baumann and Gauldie, 1994). Several acute-phase proteins have been measured in cattle with BRD, including fibrinogen, haptoglobin, serum amyloid-A, α-1-acid glycoprotein, ceruloplasmin, α-2-macoglobulin, and C-reactive protein (Carter et al., 2002), and acute-phase proteins are altered by transportation in newly weaned calves (Arthington et al., 2003a).

Initial reports suggested that haptoglobin concentration was unrelated to the
severity of the case or the need for treatment in feedlot cattle (Wittum et al., 1996b), but subsequent results suggest that haptoglobin may have value for assessing morbidity (Carter et al., 2002). Berry et al. (2004a) reported that serum haptoglobin concentrations may be useful in predicting the number of treatments required by calves, and Wittum et al. (1996b) and Carter et al. (2002) suggested that haptoglobin was of value in assessing treatment efficacy. Dietary changes in energy and starch concentration had little effect on acute-phase protein response (Berry et al., 2004a); however, Cu status of the animal may be related to acute-phase proteins before and during an inflammatory challenge (Arthington et al., 2003b).

Technological approaches might allow for early detection of morbid animals. Schaefer et al. (2005) sugfor detection of BRD. Likewise, use of radio frequency implants containing temperature probes may allow for early detection of diseases that elevate body temperature (Reid and Dahl, 2005). Research on these 2 methods conducted in commercial applications is needed to verify the accuracy of the diagnosis. If these methods proved useful, they might be included with the national animal identification system being proposed by the USDA.

Feeding and Watering

Behavior Behavioral observations may have value in diagnosing BRD. Sowell et al. (1999), using a feeding behavior system with radio frequency technology (GrowSafe Systems Inc., Calgary, Alberta, Canada), suggested that the daily number of feeding bouts was a better predictor for steers that subsequently were identified as morbid than was watering behavior. Sowell et al. (1998) reported a 30% decrease in time at the feed bunk for morbid vs. healthy steers, and differences in feed intake seemed most pronounced during the first 4 d after arrival (Sowell et al., 1998, 1999). Buhman et al. (2000) reported that sick calves had a greater frequency and duration of drinking 4 to 5 d after arrival than animals that were not sick and further suggested that drinking behavior 4 to 5 d after arrival may be an indicator of BRD.

One widely accepted stressor of beef cattle is commingling. Loerch and Fluharty (2000) suggested that when calves from various sources are commingled in feedlot pens, the social hierarchy is destroyed, and additional stress is imposed.

Calves with “trainer” cows in their pens had improved DMI during the first few days after arrival, and in some cases had improved gains and a decreased incidence of BRD (Loerch and Fluharty, 2000). In contrast, Gibb et al. (2000) reported that trainer cows did not improve calf performance, feeding behavior, or health, with calves actually avoiding cows at the bunk during the first few days in the pen. Perhaps surprisingly, Arthington et al. (2003a) reported a tendency for commingled calves to consume more daily DM over a 21-d period than noncommingled calves. Although the background of the commingled calves was unknown, previous exposure to feed bunks was offered as a possible explanation for the increased DMI.

FACTORS AFFECTING THE INCIDENCE OF BRD

Preconditioning

Most feedlot producers believe that preconditioning cattle is somewhat to extremely beneficial in decreasing morbidity and mortality in calves weighing less than 318 kg (USDA-APHIS, 2000a). Only 32.4% of all feedlots surveyed, however, received information about the previous history of the calves “always or most of the time” (USDA-APHIS, 2000b). Several formalized preconditioning programs exist, and many states have programs that certify preconditioned calves. One of the best-known preconditioning programs is the Texas A&M University Value Added Calf (Anonymous, 2005a) program. In general, preconditioning programs ensure that the animals have been weaned for a certain amount of time (usually 30 to 45 d), vaccinated (clostridial and viral vaccines), treated with anthelmintic, castrated, dehorned, and accustomed to feed bunks and water troughs.

Economics of Preconditioning

Dhuyvetter et al. (2005) suggested that based on a 45-d postweaning preconditioning program cow/calf producers can realize a $14.00 increase in returns compared with the sale of calves at weaning that are not preconditioned, and that feedlot producers also can benefit from such programs and can afford to pay premiums for pre-conditioned calves. Roeber et al. (2001) reported morbidity rates (cattle requiring at least 1 hospital visit) of 34.7, 36.7, and 77.3% and mortality of 1.1, 1.1, and 11.4% for cattle that had been subjected to 2 different preconditioning programs in Kentucky compared with auction-barn calves, respectively.

Preconditioning calves on ryegrass pastures resulted in greater ADG and decreased feed costs compared with preconditioning in a drylot (St. Louis et al., 2003), but it was not determined whether the improved performance on grass was a result of deceased morbidity or other factors.

For pasture-based preconditioning programs, an effective antibiotic regimen and vaccination program should be followed, along with pastures designed for low-stress handling of morbid animals (St. Louis et al., 2003). Preconditioning seems to be a highly effective means of decreasing BRD morbidity, but its application is not widespread. The ultimate value of preconditioning programs is the ancillary benefit of decreased morbidity in the feedlot, which may not be realized by cow/calf or stocker producers. In addition, perhaps improved information flow regarding the background of the cattle will result from the greater national emphasis on individual animal identification and trace-back, which might stimulate the demand for preconditioned calves.

Vaccination

Vaccination, including IBR, PI3, BVD, and BRSV vaccines, is an integral part of preconditioning programs. A sound working relationship between veterinarians, nutritionists, and farm/ranch managers is essential for an effective health management program. For the Value Added Calf program, vaccination is recommended 4 to 6 wk before weaning, followed by revaccination with a modified live virus at weaning (Anonymous, 2005b).

If pre-weaning vaccination is not feasible, it is recommended that calves be vaccinated at weaning and revac-cinated 14 to 21 d later. Nursing calves can be vaccinated with a product labeled for use in calves nursing pregnant cows.

Routine monitoring of the cow herd for potential viral or bacterial immunogens, or both, and administering annual boosters to the cows might result in transfer of greater levels of antibodies to the calves.

Passive transfer of antibodies in colostrum is vital for the protection of the young calf against pathogens; however, high concentrations of maternally derived antibodies might interfere with the response to vaccination (Fulton et al., 2004).

Zimmerman et al. (2006) reported that a single dose of a modified live vaccine containing BVDV administered at 4 to 5 wk of age stimulated a strong protective immune response to a challenge with virulent type 2 BVDV in calves in the presence of a high concentration of maternal antibodies against BVDV. Similarly, Patel (2005) evaluated a single intranasal vaccination with IBR and suggested the vaccine could provide significant protection in the face of maternally derived antibodies, and that this protection could be prolonged by a booster vaccination.

Monitoring both cows and calves is necessary for effective vaccination protocols. Most vaccines used are inactivated (killed) because licensing issues prevent many modified live vaccines from being used on calves nursing pregnant cows. Current practices of vaccinating calves at branding,

followed by boosters at or near weaning and at 2 to 4 wk after weaning with inactivated vaccines seem warranted (Fulton et al., 2004). Little research has been conducted evaluating the efficacy and potential interactions of viral vaccines with nutrition or management. Lysine has been hypothesized as beneficial in treating herpes simplex virus in humans, and herpes simplex virus replication is inhibited by high intracellular concentrations of lysine and low arginine (Marcason, 2003). Maggs et al. (2003) reported that a daily oral dose of 400 mg of L-lysine to cats latently infected with feline herpes virus-1 resulted in decreased viral shedding after changes in housing and husbandry but not after administration of methylprednisolone to induce viral reactivation.

Administration of ruminally inert lysine to increase serum lysine concentrations and the potential interaction with BHV-1 might deserve consideration.

Temperament

An excitable temperament in cattle negatively affects performance (Voisinet et al., 1997) and also may play a role in the response to vaccines (Oliphint, 2006; Oliphint et al., 2006). Brahman bull claves (6- to 7-mo-old) were divided into 2 groups (10 calves/temperament group) based on exit velocity from a squeeze chute and pen scores based on the response to confinement and human contact. Calves received clostridial vaccinations at the beginning of the 11-wk study and 42 d later. Both groups showed an initial antibody response by d 6 of the study, with a peak on d 13. Peak antibody response to the booster occurred on d 49 and 54 for calves classified as temperamental and calm, respectively; however, from d 49 to the end of the study, antibody response decreased 3-fold for temperamental calves, with no significant decrease for calm calves. At 11 wk, calm calves had a 1.6-fold greater antibody titer response than temperamental calves. As in previous research, calmer calves had 0.14 kg/d greater ADG than temperamental calves.

Persistent Infection with Bovine Viral

Diarrhea Virus

The prevalence of PI calves may not be great, but the economic consequences could be. Wittum et al. states for PI calves. On initial screening, a total of 56 BVDV-positive calves were found in 13 herds, and 61% of the initially positive calves remained BVDV positive at 6 mo of age. Out of 21,743 calves, Fulton et al. (2006) reported 86 PI calves, for a prevalence of 0.4%. Similarly, Loneragan et al. (2005) reported a prevalence of PI cattle was 0.3% at arrival at the feedlot; however, the prevalence of PI cattle was 2.5% in both chronically ill and dead cattle. Although the prevalence is small, PI calves affect transmission of the virus within groups of calves and associated health of cohorts. Including 1 PI calf positive for BVDV1b caused 68.4% (13 out of 19) of the calves exposed to seroconvert to BVDV1b (Fulton et al., 2005). The role of exposure to PI calves on the health and performance of cohorts is less well established. O’Connor et al. (2005) reported that a PI calf in a feedlot pen was not associated with increased disease prevalence in commingled groups. Similarly, in a recent New Mexico study, exposure to PI calves had little effect on performance of the other calves (Elam, 2006a). Heifers (296) with a known background (vaccinated once at branding with a modified live IBR, PI3, BRSV, and a killed or modified live BVD) were processed on arrival, including vaccination with modified live IBR, PI3, BRSV, BVDV types 1 and 2, vaccination for clostridial organisms, metaphylactic treatment with a commercially available antimicrobial, and treatment for internal and external parasites. The PI-BVD calves were determined using the antigen capture ELISA test and confirmed with RT-PCR. Treatments were a negative control with no PI-BVD exposure, short-term exposure (60 h) followed by removal of the PI calf from the pen, and long-term exposure (for the duration of the study). In addition, spatially exposed groups included adjacent pens to the aforementioned treatments. No animals were treated for BRD, and no differences were observed in overall ADG, DMI, or G:F by heifers exposed to PI calves short- or long-term and directly or spatially.

Castration

Castration is often a major stress imposed on newly received intact bulls. In addition, it is common to castrate bulls shortly after arrival at the feedlot at the same time that other stresses are imposed (e.g., vaccinations, horn tipping, restraint, etc.). Daniels et al. 2000) reported that calves that were castrated on arrival had a 92% greater incidence of morbidity and 3.5 vs. 0% mortality compared with those castrated before entering the feedlot. Previously castrated calves gain 0.52 kg/d ADG during a 21-d receiving period vs. 0.21 kg/d for cattle castrated on arrival. Although daily feeding and watering behaviors were not affected by castration, calves castrated before arrival had more feeding and watering bouts per day than calves castrated on arrival (Daniels et al., 2000). Age of castration also is important. As the age of castration gets closer to birth, less weight is lost for the 30-d period after castration (Bretschneider, 2005). Cow/calf producers cite concerns about decreased weaning weight (Lents et al., 2006) as a reason for not castrating bulls; however, Lents et al. (2006) reported that intact bulls did not have an advantage in BW at 6 to 7 mo of age compared with bulls banded at birth or bulls banded at birth and implanted with 36 mg of zeranol. In addition, BW gain at weaning was decreased for at least 30 d when castration was delayed to later than 6 mo of age.

Thus, producers concerned about decreased weaning weight because of castration could use estrogenic implants in suckling calves to maximize BW gain (Lents et al., 2006).

Prophylactic Medication

Preventative medication programs using prescription antibiotics are administered only under the supervision of licensed veterinarians. Economic considerations regarding the use of such programs should focus on decreasing morbidity and mortality (and associated labor issues) and improving performance. For “high risk” cattle, antibiotic therapy can be an effective means of controlling morbidity. Similarly, when morbidity and mortality are expected to be relatively low, including antibiotics in the feed of new cattle may be effective (Cole, 1993). Duff et al. (2000) evaluated the feeding of chlortetracycline at 10 mg/0.45 kg of BW for 5 d in newly received cattle. Cattle receiving chlortetracycline gained BW during the period that the antibiotic was fed, whereas the cattle not receiving the antibiotic lost weight during the same period. Including chlortetracycline in the feed near to the time of an outbreak of BRD might prove beneficial, but feed intake must be adequate to provide the proper dose of antibiotic. If feed intake of these cattle is an issue, antibiotics need to be injected to ensure the animal receives a sufficient quantity of the antibiotic.

Treatment of individual animals with antibiotics on a preventative or metaphylactic basis has been successful in decreasing the incidence of BRD. The classical work by Lofgreen (1983a), using a combination of long-acting oxytetracycline and sustained-release sulfadimethoxine, showed that morbidity was decreased from 63.3% in control calves to 7.1% in massmedicated calves. Numerous studies have demonstrated that tilmicosin phosphate is effective for decreasing morbidity of newly received, stressed cattle (Galyean et al., 1995; Cusack, 2004; Guthrie et al., 2004), and preshipping medication programs do not seem to be more effective than arrival medication programs (Duff et al., 2000). Similary, Frank et al. (2002) reported that administration of florfenicol at arrival decreased the incidence of BRD and suggested that prophylactic use of antibiotics may be a means to decrease acute BRD for several days after arrival in the feedlot. More recently, tulathromycin was effective in decreasing the incidence of BRD when given before the onset of symptoms in high-risk cattle (Rooney et al., 2005).

The exact mode of action of preventative medication programs is unknown. One organism greatly affected by prophylactic medication programs is Mannheimia haemolytica. Frank and Duff (2000) and Frank et al. (2002) reported that tilmicosin phosphate and florfenicol inhibited colonization of Mannheimia haemolytica in the nasopharnynx of cattle. Frank et al. (2002) suggested that because of this effect, administration before shipment should decrease the incidence of acute respiratory tract disease during the first week after arrival, when the cattle are most susceptible to infection; however, as noted previously, no advantage was noted with such a protocol (Duff et al., 2000).

If injectable antibiotics negatively affect DMI, beneficial effects of the antibiotics might be offset by decreased performance. Although some injectable antibiotics might decrease feed intake, Daniels et al. (2000) reported that metaphylactic antibiotics (tilmicosin florfenicol given i.m. or s.c.) did not negatively alter feeding behavior, but they decreased morbidity and increased 21-d ADG compared with untreated controls. Neither danofloxacin nor tilmicosin affected neutrophil function or apoptosis (Fajt et al., 2003), suggesting that mass medication would not enhance or diminish any nutritional effects on neutrophil function; thus, interactions of mass medication with nutritional manipulations do not seem likely, but further research is needed.

Possible interactions of antibiotics with dietary nutrients deserve attention. Cole and Hutcheson (1987) reported a tendency for increased death loss of morbid calves with 4% added dietary fat. Because of the unique lipid solubility of certain antibiotics, either positive or negative associative effects might occur that would influence their efficacy. Added dietary fat increased serum concentrations of florfenicol

Florenicol

at 6 (quadratic) and 24 (linear) h after injection compared with a diet that did not contain supplemental fat (Duff et al., 2003a). Further research should be conducted to evaluate the interaction of dietary fat with target tissue concentrations of antibiotics.

Post et al. (1991) analyzed 421 P. haemolytica and 158 P. multocida isolates, recovered from cattle with respiratory disease, for patterns of resistance to ampicillin, ceftiofur, erythromycin, gentamicin, penicillin, spectinomycin, sulfachlorpyridazine, sulfadimethoxine, tetracycline, and tylosin. All isolates tested were susceptible to ceftiofur and sulfa-chlorpyridazine.

Pasteurella haemolytica isolates were resistant to ampicillin, penicillin, sulfa-dimethoxine, tetracycline, and tylosin. Pasteurella multocida isolates were resistant to sulfadimethoxine, tetracycline, and tylosin. A study conducted in the European Union examined the sensitivity of the major BRD bacteria [M. haemolytica, P. multocida, and H. somni (formerly H. somnus)] to commonly used antimicrobials (florfenicol, tilmicosin, and tulathromycin) using disc-diffusion methods (Montgomery, 2005).

Bacterial samples were collected from cattle involved in field clinical studies of respiratory disease. The bacterial isolates included 367 M. haemolytica, 245 P. multocida, and 99 H. somni samples. The 711 different bacterial strains tested showed complete susceptibility to florfenicol, and a number of strains were resistant to or showed intermediate susceptibility to tilmicosin and tulathromycin. No mention of possible antimicrobial therapy of cattle used for sample collection was included (Montgomery, 2005). Catry et al. (2005) measured antimicrobial resistance of Pasteurella and Mannheimia isolates from 57 calves in 13 dairy herds, 150 calves in 9 beef cattle herds, and 289 calves from 5 high-density veal calf herds. The overall resistance of the isolates to at least 1 antimicrobial was 17.6% for dairy, 21.9% for beef, and 71.9% for veal herds. They further reported that resistance to ceftiofur and florfenicol was not detected.

Likewise, Rosenbusch et al. (2005) reported that florfenicol was found to be active in vitro against Mycoplasma bovis. Montgomery (2005) recommended frequent review of treatment protocols and that veterinarians evaluate case histories of any previous pneumonia outbreaks on a farm to determine the best intervention strategy. Given that the earlier work of Post et al. (1991) reported resistance to ceftiofur and the later work by Catry et al. (2005) revealed no resistance to ceftiofur, antibiotic resistance to ceftiofur is doubtful; however, more detailed information on previous antibiotic use in all cases needs to be reported before a definitive answer can be given. Because of the importance of antibiotics in therapeutic treatment of BRD, however, antimicrobial resistance needs to be monitored closely.

Non-antibiotic Alternatives

Given the potential for antibiotic resistance, evaluating alternatives to antibiotics is an important area of future research. In a pilot study using 13 weaned and transported calves, Schaefer et al. (2005) suggested that nitric oxide (administered via a nasal tube for 3 consecutive days at 160 or 200 ppm prophylactically or on early detection of BRD) may be an effective treatment. Rivera et al. (2003b) evaluated the effects of an intranasal lysozyme/carbopol preparation given at the time of arrival on health and performance of newly received calves. No differences were noted for ADG or G:F for the 28-d receiving period, but the preparation tended to decrease DMI and tended to increase morbidity during the receiving period. The authors speculated that the lysozyme preparation may have killed beneficial organisms in the nasopharynx, which could have facilitated colonization by M. haemolytica, P. multocida, or both. Research is needed to evaluate administration of lysozyme further down the respiratory tract or at different times after arrival.

Direct-fed microbials (DFM) might be useful to improve performance and decrease morbidity of newly received beef calves. From data collected by member feedlots reporting to the VetLife Benchmark Performance Program, McDonald et al. (2005) evaluated records on 73,870 lots containing 10,900,504 cattle.

Feedyards using DFM had increased ADG of 1.9 and 1.4% for steers and heifers, respectively, along with 1.9 and 3.9% improvements in the efficiency of gain. Moreover, ancillary benefits of DFM might occur via improved health or response to antibiotic treatments.

Performance advantages with DFM were much greater in cattle with greater (more than $20 per animal) processing and medical treatment charges (Mc-Donald et al., 2005). Krehbiel et al. (2003) and Beauchemin et al. (2006) recently reviewed the use of DFM in ruminant diets. Krehbiel et al. (2003) cited a study conducted in their laboratory in which no difference in ADG was observed with DFM; however, calves receiving DFM as an oral gel during their first antimicrobial treatment were less likely to be treated again within 96 h, and fewer calves required a second treatment compared with those not given the gel. Krehbiel et al. (2003) suggested that DFM might be beneficial for newly received calves but also pointed out that Gill et al. (1987; as cited by Krehbiel et al., 2003) suggested that DFM might have limited value for extremely healthy or extremely sick calves. As with feed-grade antibiotics, attaining the desired intake of the product may pose problems for morbid calves.

The exact mode of action of DFMremains to be determined; however, Krehbiel et al. (2003) and McDonald et al. (2005) proposed alteration in intestinal microorganisms (including potential effects on ruminal fermentation) and thus competitive attachment of DFM vs. pathogens, as well as superior immune responses or greater gut permeability as possible factors responsible for improved health, performance, or both.

NUTRITIONAL STATUS EFFECTS

The nutritional status of cattle before a BRD challenge is likely critical to the outcome of the challenge. Effects of nutrition or stress during pregnancy on subsequent adult health (fetal programming) are topics of considerable interest in human nutrition (Moore, 1998; Godfrey and Barker, 2001; Owen et al., 2005). Fetal programming also has effects on livestock performance and health (Wu et al., 2006), but relationships between pre- or early postnatal nutrition and susceptibility to BRD in beef cattle have not been defined. As noted previously, effective passive transfer of immunoglobulins in colostrum is vital to calf health and immunity early (Perino, 1997) and later in life (Wittum and Perino, 1995). Perhaps somewhat surprisingly, little is known about the effects of plane of nutrition before a BRD challenge on the health and immunity of beef cattle. Indeed, the nutritional background of cattle used in practical experiments with BRD is typically unknown. Variation in nutritional status might explain the large variation in response to nutritional supplements, particularly protein, minerals, and vitamins, that is evident in the BRD literature.

For example, previous grazing of endophyte-infected fescue pastures might influence receiving period performance, and such cattle received during extreme hot or humid conditions, or both, may experience up to a 10% death loss unless they are cooled with water (personal communication, R. W. Sprowls, Texas A & M Veterinary Diagnostic Laboratory, Amarillo). The duration of carryover effects from fescue toxicosis have
been reported to vary from 8 to 10 d (Aiken et al., 2006) to 14 d (Cole et al., 2001). Using cattle with a documented nutritional and management history might be preferable to using cattle from unknown backgrounds, but such cattle might be less likely to succumb to BRD (see the previous discussion on preconditioning, and Clark et al., 2006) and therefore less effective for modeling the disease. Applying nutrient depletion or repletion approaches to cattle for a known period of time before an immune system challenge might be a useful approach to evaluate the efficacy of nutritional or management changes. Although such experimental approaches would no doubt provide more precise estimates of the effects of nutritional or management modifications on health and immunity, well designed experiments in “real world” settings will continue to be important for field application.

Dietary Energy Concentration

Energy restriction that does not result in malnutrition has increased the life span in rodent models, and it seems beneficial to immunity through increasing lymphocyte proliferation, attenuating age-related decreases in interleukin-2 production, and potentially modifying signal transduction in T-cell development and function (Pahlavani, 2000). Similarly, in periparturient, ruminally cannulated dairy cows with Johne’s disease, the neutrophil responses to concanavalin A, phytohemagglutinin (PHA), or pokeweed mitogen were decreased in cows receiving additional feed through the cannula (Stabel et al., 2003); however, immunoglobulin secretion by peripheral blood mononuclear cells was increased in these cows, suggesting positive effects of added energy intake on some aspects of immune cell function.

In Holstein steers fed 210 or 60% of maintenance requirements, negative energy balance had little effect on the expression of adhesion molecules by leukocytes, and expression was increased by negative energy balance in some cases (Perkins et al., 2001). Nonetheless, Ritz and Gardner (2006) noted that aged, energy-restricted mice could not survive a primary influenza infection, and suggested that their innate immune function was diminished. Moreover, the low BW of energy-restricted mice contributed to the mortality because their body energy reserves were inadequate to withstand the infection. Because previously reported positive effects of energy restriction had been observed in challenges with influenza vaccine, Ritz and Gardner (2006) suggested that immunization should not serve as the sole response criterion for the immune response to viruses. Whether the effects on immunity noted with energy in aged rodent and primate models can be applied to lightweight, typically younger, beef cattle is open to question, but adequate energy intake and body energy stores should be important for all bodily functions, including immunity. Because the energy concentration in beef cattle diets is typically altered by changing the dietary roughage concentration, few studies have evaluated changes in energy intake alone. Thus, effects of energy intake are often confounded with changes in dietary ingredients, particularly roughage. In summarizing classical research on dietary preferences of lightweight, stressed cattle, Lofgreen (1983b) noted such cattle have (1) an abnormally low feed intake relative to BW; and (2) a preference for and greater consumption of a high concentrate than a high-roughage diet. When given a choice among feed mixtures varying in concentrate level during the first week after arrival at the feedlot, stressed calves selected diets with 72% concentrate (Lofgreen, 1983b). Thus, intake and performance by lightweight, newly received calves is typically optimized with greater compared with lower concentrate diets.

Calves started on a 75% concentrate diet, with or without long-stemmed alfalfa hay during the first week after arrival, gained more and ate more feed than those started on hay alone (Lofgreen, 1979). However, Lofgreen et al. (1981) reported that notwith-standing improved performance, calves fed a 75% concentrate diet tended to have more total sick days than those fed hay alone, although overall proportions of animals treated for BRD did not differ among diets. Fluharty and Loerch (1996) found that as dietary concentrate increased from 70% to 85% in newly received cattle, DMI, but not ADG, increased, and morbidity was not affected by the proportion of dietary concentrate. Berry et al. (2004 a, b) attempted to sort out the confounding effects of roughage and energy concentrations by feeding high and low starch concentrations within each of 2 dietary roughage concentrations. Energy concentration did not influence performance or overall morbidity, but morbid calves fed the greater energy diets had less shedding of P. multocida and H. somnus than those fed the lower-energy diets. Dietary roughage concentration varied over a fairly narrow range of 35 to 45% in the Berry et al. (2004a,b) studies, and comparison with results of Lofgreen et al. (1981), where the variation in roughage/energy concentration was much greater, is not possible. Whitney et al. (2006) fed Bermuda grass hay alone, hay with 0.175 or 0.35% of BW of supplemental soybean meal, or a 70% concentrate diet for an 84-d backgrounding phase in early weaned beef steers. Calves fed the concentrate diet had greater DMI and ADG than those fed the hay-based diets. After 84 d, all cattle were switched to the 70% concentrate diet and challenged with an intranasal dose of BHV-1. Serum IgG concentrations were greater before and after the challenge in cattle fed the hay-based diets during backgrounding.

Although the differences were small, average rectal temperature on the day after the challenge was greater in calves that were fed the concentrate diet during the back-grounding period, suggesting these calves had a more intense febrile response than the calves fed the hay diets. Perhaps the increased sick days in calves fed greater concentrate diets noted by Lofgreen et al. (1981) reflects enhanced proinflammatory cytokine and febrile responses compared with their counterparts fed lower-energy roughage based diets.

To evaluate the statistical relationships between BRD and dietary roughage concentration in lightweight, stressed cattle, Rivera et al. (2005) analyzed data collected by Glen Lofgreen at the New Mexico State University Clayton Livestock Research Center.

Diets ranged from all-hay to 75% concentrate. Relationships between dietary roughage concentration (DM basis) and receiving-period morbidity, ADG, and DMI were evaluated with mixed-model regression methods. Morbidity (e.g., percentage of calves treated for BRD using visual observation and rectal temperature as a means of diagnosis) decreased slightly as dietary roughage concentration increased [morbidity, % = 49.59 − (0.0675 × roughage, %); P = 0.003]. The ADG and DMI were affected negatively (P < 0.001) by increasing the dietary roughage concentration, and economic analysis indicated that the slightly lesser morbidity noted with greater roughage concentrations would not offset the loss in profit resulting from decreased ADG. Rivera et al. (2005) concluded that greater concentrate, milled diets would likely provide stressed, newly received cattle, with limited effects on BRD.

As noted previously, treating cattle for BRD has long-term consequences on feedlot performance and carcass characteristics. Similarly, decreasing energy intake during the receiving period seems to affect ADG, and calves fed low-quality, hay-based diets during receiving were unable to compensate for lost gain during subsequent finishing (Lofgreen 1983b, 1988). Perhaps caloric restriction during a time when the hypothalamic-pituitary-adrenal axis is activated, whether imposed by type of diet fed or as a result of negative health events, results in a permanent loss of performance.

Using model systems to evaluate long term performance effects of caloric restriction during stress would seem to be a good area for research.

Dietary Protein Concentration

In mice fed protein-free diets for 2 to 3 wk, bactericidal immune defense mechanisms were not affected, despite severe weight loss; however, protein deficiency resulted in a failure of the mice to eliminate influenza virus from the lungs, and viral infection suppressed bactericidal defenses (Jakab et al., 1981). Dai et al. (1998) reviewed the effects of nutrition on host responses to mycobacteria and concluded that with diseases like tuberculosis, protein malnutrition resulted in the loss of T-lymphocyte functions and cell-mediated resistance. Moreover, they suggested that generation, migration, or maturation of monocytes was negatively affected by protein deficiency, and that secretion of cytokines (interleukin-2 and interferon-γ) by these cells was impaired in protein-deficient animals. Conversely, transforming growth factor-β production by macrophages infected with Mycobacterium tuberculosis was increased in protein deficiency, which resulted in immunosuppressive effects. Thus, severe protein malnutrition can result in negative effects on immune function. Protein and energy deficiency are often confounded through negative effects of low-protein diets on energy intake, however, and attributing the effects on immunity noted in many experiments solely to protein deficiency is probably incorrect.

We previously concluded that although morbidity from BRD seemed to increase with increasing CP concentration in diets of newly received calves, ADG and DMI also increased as CP concentration increased (Galyean et al., 1999). This paradoxical response was attributed to 3 possible scenarios: (1) inaccurate diagnosis of BRD; (2) morbid calves fed greater-CP diets had greater performance than morbid calves fed lower-CP diets; or (3) performance by healthy calves within greater-CP diets was greater than by healthy calves fed the lower-CP diets. We further suggested that the effects of dietary CP concentration on immune function needed to be assessed; however, to our knowledge this has yet to be fully accomplished.

In neonatal calves, feeding a greater quantity of milk replacer with greater protein content had limited effects on the composition and functionality of peripheral blood mononuclear cell populations compared with calves fed a lower intake of a standard milk replacer (Foote et al., 2005). In early weaned calves fed Bermuda grass hay (6.7% CP, DM basis) alone or hay plus soybean meal at 0.175 or 0.35% of BW, ADG and DMI were increased during an 84-d backgrounding period by the supplemental protein, but no difference was found between the 2 supplemental protein levels (Whitney et al., 2006). When challenged with an intranasal dose of BHV-1, calves previously fed supplemental protein had greater average rectal temperatures for d 1, 2, 4, and 5 after the challenge than calves previously fed hay alone. Serum IgG concentrations after the virus challenge were not affected by protein
supplementation. Considering the results of Whitney et al. (2006), and our previous observation (Galyean et al., 1999), calves fed greater CP diets might have an increased likelihood of being diagnosed with BRD as a result of elevated body temperature.

Nonetheless, our suggestion that additional research is needed on the effects of dietary CP concentration on immune function in stressed cattle still seems to have merit.

Minerals

Because of low DMI, concentrations of most minerals need to be increased in receiving diets (NRC, 1996). In our earlier review of the potential effects of Cr, Cu, Se, and Zn supplementation on immune function, BRD morbidity, and performance by newly received calves, we noted that although some trials had shown immune function and health benefits from these minerals, many experiments had not (Galyean et al., 1999).

Since that review, several reports have been published, particularly on Cu, Se, and Zn; however, little additional information beyond what we reported in 1999 seems to be available for Cr.

Copper

Despite evidence that Cu is essential for immune function (Percival, 1998), the results of experiments that we reviewed previously did not provide compelling evidence for consistent effects on immunity and provided only limited evidence of responses to Cu supplementation in field studies with stressed calves (Galyean et al., 1999). Although it has been suggested that neutrophil function might be a valuable biomarker of Cu status (Bonham et al., 2002), chemotaxis and adhesion molecule expression of neutrophils in cattle did not seem to be greatly affected by substantial changes in Cu status induced by Mo and S (Arthington et al., 1995, 1996).

Ward and Spears (1999) injected Angus bull calves with 90 mg of Cu glycinate 28 d before weaning and subsequently supplemented these calves with Cu from CuSO4 (7.5 and 5 mg/kg of DM during the receiving and growing phases, respectively). Control steers did not receive supplemental Cu during the study. During the growing phase, half of the steers in each Cu treatment group were supplemented with 5 mg of Mo/kg of DM, and at d 168 half of the steers were stressed by loading and transport. Supplemental Cu did not affect the skin-swelling response to PHA during the receiving period but increased the antibody response to ovalbumin during the growing phase. Moreover, supplemental Cu increased antibody titers to porcine red blood cells in calves that were subjected to loading and transport stress but decreased the titers in unstressed calves. The authors concluded that specific immunity of stressed cattle was not greatly affected by Cu deficiency and supplemental Mo. Bailey et al. (2001) fed Angus × Hereford heifers a basal grass hay-based diet that contained 6 mg of Cu/kg of DM or supplemented the basal diet with 49 mg/kg of DM as CuSO4; 22 mg/kg from CuSO4; 22 mg/kg from a 50:50 combination of CuSO4 and Cu-amino acid complex; or 22 mg of Cu/kg from a mixture of CuSO4, Cu-amino acid complex, and CuO (25:50:25). All diets contained added Mo, S, and Fe. Treatments did not affect ADG or cell-mediated immune function, but the combination of 22 mg/kg from CuSO4 and Cu-aminoacid complex was as effective at limiting liver Cu loss as feeding 49 mg of Cu/kg from CuSO4.

Source and level of supplemental Cu might have effects on other factors besides immunity and health that could affect performance. A bolus containing 12.5g of CuO needles increased liver Cu concentration after 12 and 33 d in steers fed limpograss hay (Arthington, 2005), but steers in the CuO bolus group had lower NDF and CP digestibilities. In a second experiment, heifers fed stargrass hay were provided 0, 15, 60, or 120 mg of Cu/kg from CuSO4 in a molasses-cottonseed meal supplement. Feeding 15 mg of supplemental Cu/kg of DM was more effective at maintaining liver Cu than greater concentrations. Heifers fed supplemental Cu tended to eat more forage than controls during the first 2 wk of a 12-wk period, but DM digestibility was not affected by Cu level. Measures of immune function were not reported.

Selenium

If organic complexes of minerals are more bio available than inorganic ones, an organically complexed mineral might be beneficial in preventing or correcting deficiencies during stress and periods of low feed intake (Greene, 1995). With the development of Se-enriched yeast, research that has been published on Se since our previous review has largely focused on comparisons between Se-yeast and inorganic Se.

In cows and calves fed mineral supplements containing no supplemental Se or 26 mg of Se/kg of DM from sodium selenite or Se-yeast, Beck et al. (2005) evaluated lymphocyte blastogenesis and the skinswelling response to PHA in the calves after weaning. Based on whole blood Se and glutathione peroxidase activity, control calves were deficient in Se. Lymphocyte proliferation response to mitogens was not affected by treatment, but macrophage phagocytosis was increased in calves supplemented with Se-yeast compared with control and sodium selenite calves. Skin swelling response after injection of PHA tended (P =0.12) to be increased by Se sup-plementation, but it was not affected by Se source. Fry et al. (2005) fed Angus-crossbred calves fescue hay plus a corn-soybean meal supplement that provided no supplemental Se or 1.7 mg of supplemental Se/d from sodium selenite or Se-yeast. Both sources increased whole-blood Se, with the effects being more rapid in the Se-yeast group, but lymphocyte proliferation and phagocytosis did not differ among treatments. Hence, although Se-yeast might be more bio available in terms of the effects on whole-blood Se and other measures of Se status, additional research is needed to fully elucidate its effects on immune function.

Although Arthur et al. (2003) indicated that adequate dietary Se is considered vital for practically all components of the immune system, Suttle and Jones (1989) concluded that the evidence was not strong that Se affected resistance to infection in ruminants. We would not alter this conclusion substantially based on the data available since our previous review.

Zinc

Beneficial effects of supplemental Zn for the prevention of pneumonia and diarrhea, or as an adjuvant to antimicrobial therapy for the treatment of pneumonia, are typically observed in Zn-deficient children (Hambidge, 2006). Likewise, beneficial effects of supplemental nutrients on immunity and the incidence of BRD in beef cattle would be most likely in animals with a marginal or deficient status of the nutrient.

As noted previously, however, it is highly unusual to know the nutrient status of cattle used in most applied receiving studies. Mineral source, particularly of Zn, was a major focus of our 1999 review, and the results of additional experiments have been published since then with Zn in various inorganic and organically complexed forms. Gunter et al. (2001) supplemented steers with 103 mg of Zn/d from ZnSO4, Zn-amino acid complex, or Zn-polysaccharide during a 116-d grazing period on Bermudagrass pastures, after which the steers were shipped (14 h) to a research feedlot, where they continued on the same Zn sources that were fed during grazing.

Neither grazing nor feedlot performance or serum Zn concentrations were affected by Zn source, nor was the number of steers treated for BRD. Spears and Kegley (2002) fed Angus steers (246 kg of initial BW) growing (silage-based) and finishing (corn-based) diets with no added Zn or 25 mg of supplemental Zn/kg of DM from
ZnO and 2 different zinc proteinates. All 3 sources of supplemental Zn increased ADG during the growing period, as well as carcass quality grade, whereas the 2 protein ates tended to increase finishing period ADG and improve G:F compared with ZnO.

Lymphocyte blastogenesis and humoral antibody titers after IBR vaccination during the growing period did not differ among treatments. Mineral Combinations. In Angus and Simmental steers fed silage-based diets with 1,000 mg of supplemental Fe/kg for 149 d (Mullis et al., 2003), Cu and Zn supplemented in sulfate or proteinate forms to supply 5 mg of Cu and 25 mg of Zn/kg of DM did not affect performance or liver Cu and Zn concentrations. Liver Cu decreased with time on feed, and increasing the Cu to 10 mg/kg of DM did not prevent the decrease. Salyer et al. (2004) evaluated health and performance responses of newly received heifers to dietary sup-plementation of Cu (10 mg of Cu/kg of dietary DM) and Zn (75 mg of Zn/kg of dietary DM) from sulfate and polysaccharide mineral complex sources. Effects of these same mineral sources on the humoral immune response to ovalbumin also were measured.

Copper source × Zn source interactions were not detected for any variable. Neither Cu nor Zn source affected DMI, ADG, G:F, or BRD morbidity in the receiving study. Titers to ovalbumin were greater on d 14 (P = 0.02) and 21 (P = 0.06) after injection of ovalbumin in heifers that received the Zn-polysaccharide complex than in ZnSO4 heifers. In contrast, heifers receiving CuSO4 had greater titers to ovalbumin than those receiving the Cu-polysaccharide complex treatment on d 14 (P =0.01) and 21 (P = 0.001). Thus, Cu and Zn sources affected the antibody response to ovalbumin, but source effects were not consistent for the 2 minerals. Providing free-choice mineral supplements composed of all inorganic vs. half to two-thirds of the supplemental minerals from proteinate complexes of Cu, Mn, and Zn (10, 25, and 25 mg/kg of DM, respectively), with or without 0.15% supplemental P, to cows and calves before weaning and to calves after weaning had little effect on immune function measurements in newly weaned steers challenged with an intranasal inoculation of IBR virus (Engle et al., 1999). In a second experiment, in which the same treatments were repeated before and after weaning, receiving period performance was not affected, but plasma Cu was increased in calves fed the organically complexed mineral supplements (Engle et al., 1999).

Stanton et al. (2000) supplemented Angus cows and their calves with a low level of inorganic forms of Co, Cu, Mn, and Zn vs. high levels (2.1× for Cu, 1.44× for Mn and Zn, and 10× for Co vs. the low level) of inorganic or amino acid-complexed minerals and found no effect of treatments on the skin-swelling response to PHA in calves. Crossbred steer calves were arranged in a 2 × 2 factorial by Stanton et al. (2001) to evaluate the effects of high and low levels of inorganic or organically complexed trace minerals fed before and after weaning on performance and immune function. Iron, S, and Mo were added to all diets. Performance over 237 d was not affected by trace mineral source or level; titers to respiratory virus vaccines did not differ among treatments, and the skin-swelling response to PHA was not affected by trace mineral source or level. Clark et al. (2006) treated low- and high-risk steer calves with a 5-mL (s.c.) injection containing Cu, Se, Mn, and Zn, and measured BRD morbidity (incidence of undifferentiated fever) and performance during a 28-d receiving period and subsequent finishing period.

Low-risk calves were vaccinated against common diseases and weaned 45 d before the experiment, whereas high-risk calves were purchased via auction markets and were of unknown history. The incidence of undifferentiated fever was 64.4% in high-risk calves vs. 2% in low-risk calves, but it was unaffected by trace mineral injection. Trace mineral injection decreased ADG during the receiving period, but G:F was improved by the trace mineral injection for the finishing period. In our earlier review (Galyean et al., 1999), we concluded that formulation of receiving diets should account for decreased DMI by highly stressed, newly received beef cattle and for any known nutrient deficiencies but that adding trace minerals to such diets beyond the concentrations needed to compensate for low feed intake is difficult to justify. Based on the additional data available since that review, we see no reason to substantially modify that conclusion. In addition, although there is some evidence that organically complexed mineral sources might occasionally have different effects on performance and immune function, the effects seem too variable to recommend feeding particular sources.

Vitamins

B Vitamins and Vitamin A. Results with supplemental B vitamins in the diets of newly weaned/received cattle have been variable (alyean et al., 1999), and there seems to be little justification for B-vitamin supplementation of nutritionally balanced receiving diets. Nonetheless, the practice of providing injections of B-vitamins is common in feedlots (31.4% of all feedlots surveyed; USDA-APHIS, 2001) as part of BRD treatment regimens, presumably as this is thought to stimulate immunity or perhaps feed intake. In a stress/BHV-1 challenge model, Dubeski et al. (1996) noted that calves given an injection of B-vitamins and ascorbic acid had a nonsignificant increase in IgG titers to BHV-1 on d 14 and 28 after the challenge, but BW change and lymphocyte blastogenesis did not differ between treatments. Controlled studies to test the use of B-vitamin injections as an adjunct therapy for BRD treatment would be beneficial.

Vitamin A plays an important role in immune function, and vitamin A deficiency in humans and rats is associated with increased severity of infection (Twining et al., 1997). Chemotaxis and phagocytosis by neutophils was decreased in vitamin A-deficient rats, but these abilities were quickly restored by supplemental vitamin A. Semba (1999) reviewed the role of vitamin A in immunity and clinical outcomes of various human diseases. The efficacy of supplemental vitamin A in human trials has varied considerably, and trials with lower-tract respiratory infections have not shown marked clinical benefits (Semba, 1999). With respect to BRD, it would be important to provide vitamin A to calves that have a known deficiency or are potentially marginal in vitamin A status, with injection of vitamin A likely being the most rapid means of increasing body stores. In the absence of a frank deficiency, however, it would seem unlikely that supplemental vitamin A would have major effects on the incidence of BRD. Vitamin E. Carter et al. (2002) fed diets to provide 2,000 IU of vitamin Eanimal−1d−1 for 0, 7, 14, or 28 d after the arrival of 4 groups of lightweight heifers.

Average daily gain was not affected by treatment, but the medical treatment cost was less for cattle fed supplemental vitamin E for 28 d. By d 28, serum amyloid-A concentrations were less in heifers that had been supplemented with vitamin E, as were α-1-acid glycoprotein concentrations, but fibrinogen and haptoglobin
concentrations were not affected by vitamin E supplementation. Carter et al. (2005) evaluated the same vitamin E treatments in 7 truckloads of lightweight cattle during 42-d receiving studies. The duration of supplemental vitamin E feeding did not affect ADG and G:F. As in Carter et al. (2002), which seemed to include a subset of the animals used in Carter et al. (2005), medical costs were decreased for calves fed were greatest on d 28 for calves fed vitamin E for the 28-d period and decreased as the length of supplementation decreased, leading Carter et al. (2005) to conclude that the effects of vitamin E on health were likely time-dependent. Rivera et al. (2002) evaluated receiving diets containing 285, 570, or 1,140 IU of vitamin Eanimal−1d−1 in two 28-d receiving studies, 1 with steers and 1 with heifers. Vitamin E level did not affect ADG, DMI, or G:F during the receiving period; however, similar to the results of Carter et al. (2005), the greatest dose of supplemental vitamin E tended (P < 0.14) to decrease the BRD retreatment rate. In an experiment with beef steers, serum IgG titers to ovalbumin increased linearly with increasing dose of vitamin E. Rivera et al. (2003a) tested the effects of the same 3 doses of vitamin E used in their receiving studies on febrile and metabolic responses in individually fed steers after an intranasal challenge with IBR. Rectal temperature increased linearly in response to vitamin E dose on d 2 and 3 after the challenge, but vitamin E did not affect ADG or serum insulin, NEFA, and urea N concentrations. It was suggested that vitamin E supplementation increased the inflammatory response, which might explain the positive effects on humoral immunity reported by Rivera et al. (2002). Elam (2006b) summarized data from Secrist et al. (1997), Rivera et al. (2003a), Carter et al. (2005), and Cusack et al. (2005) using mixed model statistical methods to evaluate the effects of vitamin E intake on performance and health of newly received cattle. Supplemental vitamin E intake ranged from 0 to 2,000 IUanimal−1d−1. Average daily gain, DMI, and G:F were not significantly related to intake of vitamin E; however, BRD morbidity decreased (P = 0.08) by 0.35% for every 100 IU increase in daily vitamin E intake.

In our 1999 review (Galyean et al., 1999), we concluded that vitamin E at doses of greater than 400 IUanimal−1d−1 seemed beneficial for increasing ADG and decreasing BRD morbidity. Results of the experiments reported since then are generally supportive of the positive effects of supplemental vitamin E on BRD
morbidity but perhaps less indicative of the effects on ADG than we had previously concluded.

Other Dietary Considerations

Several other dietary factors might need special attention in receiving diets. Stressed calves are said to prefer dry diets over corn silage-based diets (NRC, 1996), and it is commonly recommended to avoid the use of silage in diets for lightweight, stressed cattle.

Whether avoidance of wet ingredient diets is applicable to other feed stuffs (e.g., wet corn gluten feed, distiller’s grains) or to only fermented feeds like silage is open to question, and direct comparisons between diets based on silage vs. hay-grain combinations are limited.

Limiting fat in receiving diets has been recommended (NRC, 1996). Added fat (4%) in receiving diets did not greatly affect performance, but it increased mortality compared with no added fat (Cole and Hutcheson, 1987). Fluharty and Loerch (1997), however, reported no effect of added fat (0 or 4% from an animal/vegetable blend or from calcium soaps of fatty acids) on morbidity and mortality of newly received cattle, and the animal/vegetable blend improved G:F compared with no added fat and calcium soaps of fatty acids.

Based on a review of several articles, Cole (1996) recommended that urea concentrations in receiving diets be restricted to limit total urea intake to less than 0.5 to 0.75% of DM. Nonetheless, Duff et al. (2003b) reported that including urea at 1% of the dietary DM in a 70% concentrate diet for newly received calves did not affect performance or BRD morbidity during a 28-d receiving period. Because ionophores can negatively affect DMI, their concentrations are often limited in receiving diets to avoid these negative effects. Duff et al. (1995) compared a no-ionophore control diet with diets containing lasalocid at 33 mg/kg, and monensin at 22 or 33 mg/kg of the dietary DM. Ionophores decreased (P < 0.08) DMI compared with the control diet for the 28-d trial, but ADG and the efficiency of gain were not altered by treatments. Numerically, monensin at 33 mg/kg resulted in a lower DMI than lasalocid at the same concentration. All 3 ionophore treatments decreased the presence of coccidial oocysts. Thus, ionophores might have negative effects on DMI in newly received cattle, but these effects can be moderated by the choice of ionophore or, with monensin, by decreasing the dietary concentration.

SUMMARY AND CONCLUSIONS

Several viruses/bacteria interact to cause BRD, with M. haemolytica being the bacterial organism most often isolated. The effects of PI BVDV on transmission of virus and performance may be important in the development of BRD, but more research is needed.

Our ability to diagnose BRD is less than optimal, and development of cost-effective, quantitative methods to more accurately detect animals afflicted with or likely to develop BRD would be valuable to the beef cattle industry. Preconditioning programs offer significant potential to decrease the incidence of BRD, and programs should include vaccination for viral agents and castration of bull calves. Metaphylactic antimicrobial programs continue to be an effective management option for high-risk beef calves, but close attention should be given to antimicrobial resistance, and alternative methods for prevention and/or treatment of calves for BRD deserve attention.

The nutrient status of animals purchased through commercial marketing channels and subsequently arriving at feedlots is rarely known, making it difficult to design diets to provide adequate nutrition and to predict the responses to supplemental nutrients.

After decades of research, our ability to modify the incidence of BRD through nutritional manipulations seems limited. The same nutritional program applied to different groups of cattle under seemingly similar conditions may result in widely different rates of BRD morbidity.

Based on our review, we recommend that the nutrient content of diets for newly received cattle be formulated to adjust for the low feed intake associated with stress. Adding greater concentrations of vitamin E may be beneficial for decreasing BRD, but research results with trace minerals are variable. Diets with increased energy density (e.g., increased concentrate feeds) that are formulated to provide adequate protein and other nutrients are likely to increase ADG and G:F compared with low-energy receiving diets, without substantially altering the occurrence of BRD.

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July 2, 2019

Commingling Calves and Respiratory Disease

Octavoscene Livestock Diseases Bovine Respiratory Disease, Calf Commingling, Performance, Stress

We would like to invite farmers to keep a farmers’ day in their area regarding the study done in this particular article. This has been a very informative study and we think every cattle farmer can benefit from this.

Please contact the Octavoscene Head Office if you are planning to hold such a day in your area. Dr Shaun Morris (BVSc (Hons) MSc Agric), Director of Octavoscene (Pty) Ltd, a specialist feedlot expert and veterinarian, would like to assist you with the training and we will help to make this event a very successful day.

This is a relatively long article and the study is about the following topic:

Effects of commingling beef calves from different sources and weaning protocols during a forty-two-day receiving period on performance and bovine respiratory disease

D. L. Step*,3, C. R. Krehbiel†, H. A. DePra†, J. J. Cranston†; R. W. Fulton**, J. G. Kirkpatrick*, 5D. R. Gill†,M. E. Payton‡, M. A. Montelongo**, andA. W. Confer** 67*Departments of Veterinary Clinical Sciences and **Veterinary Pathobiology, Center for 8Veterinary Health Sciences;†Department of Animal Science, Division of Agricultural Sciences 9and Natural Resources;and ‡Department of Statistics, College of Arts and Sciences, Oklahoma 10State University, Stillwater, OK 74078.

Approved for publication by the Director of the Oklahoma Agricultural Experiment Station. This research was supported under project H-2438 and a grant from the Noble Foundation. The authors acknowledge R. Ball, B. Starr, and students from the Willard Sparks Beef Research Center for providing processing, animal care, and record keeping expertise, and Cattleco, Inc. for 25providing cattle. Corresponding author:dl.step@okstate.edu

ABSTRACT

The study objective was to determine health and performance of ranch calves from different pre-conditioning strategies during a 42-d receiving period when commingled with calves of unknown health histories from multiple sources. Steer calves from a single source ranch (RANCH) were weaned and immediately shipped to a feedlot (WEAN, initial BW = 247 ± 3129 kg); weaned on the ranch for 45 d before shipping, but did not receive any vaccinations (WEAN45, initial BW = 231 ± 26 kg); or weaned, vaccinated with modified live viral vaccine, and held on the ranch for 45 d before shipping (WEANVAC45, initial BW = 274 ± 21 kg).

Multiple-source steers were purchased through auction markets (MARKET, initial BW = 238 ± 3513 kg), and upon receiving, a portion of ranch-origin steers from each weaning group were commingled with a portion of MARKET cattle (COMM). The experimental design was completely randomized with a 2×3+1 factorial arrangement of treatments. Factors were RANCH vs. COMM and weaning management (WEAN vs. WEAN45 vs. WEANVAC45) as the 39factors; MARKET cattle served as the control. Calves of WEAN, WEAN45, and MARKET were vaccinated on arrival at the feedlot. Ranch-origin calves tended (P = 0.06) to have greater ADG than COMM or MARKET calves, although ADG was not affected (P = 0.46) by weaning management. Across the 42-d receiving period, DMI was not affected (P = 0.85) by cattle origin. However, MARKET, WEAN45, and WEANVAC45 calves consumed more (P < 0.001) 44DM than WEAN calves. Gain efficiency was not affected (P> 0.11) by treatment. Ranch-origin 45calves were less (P < 0.001) likely to be treated for bovine respiratory disease than MARKET calves; COMM calves were intermediate. Calves that were retained on the ranch after weaning (WEAN45 and WEANVAC45) were also less likely to be treated (P = 0.001) than MARKET or WEAN calves. As expected, differences in morbidity related to differences in health costs. Calves of WEAN45 and WEANVAC45 had lower (P < 0.001) health costs than MARKET and WEAN calves. On arrival, serum haptoglobin concentrations were greater (P < 0.001) in MARKET and WEAN compared with WEAN45 and WEANVAC 45 calves. Calves from a single source that are retained on the ranch for 45 d after weaning exhibit less morbidity and lower health costs during the receiving period at the feedyard than when cattle are commingled or trucked to the feedyard immediately after weaning.

INTRODUCTION

Bovine respiratory disease (BRD) involves the complex interaction between infectious agents, the environment,and stress (Galyean et al.,1999). Fulton et al. (2002) reported that calves treated for BRD once returned $40.64 less, calves treated twice returned $58.35 less, and calves treated 3 or more times returned $291.93 less than calves that were not treated. Therefore, management strategies to decrease the incidence of BRD would likely increase economic returns. Marketing practices in the U.S. beef cattle industry can result in varying periods of stress, nutritional deficiencies, and exposure to infectious agents when calves are commingled from various sources, transported to distant sites, and changes in diet and/or feed intake are abrupt. Limited data and practical experience have provided evidence that the effects of BRD on beef cattle morbidity and mortality can be decreased through pre-transport preventive health programs commonly referred to as preconditioning, which may include vaccination for various infectious agents, anthelmintic treatments, exposure to feed bunks and troughs, and delayed shipment for 3 to 6 wk after weaning (Duff and Galyean, 2007). Due to the large population of cattle at risk of developing BRD in post-weaning production, data evaluating the efficacy of various weaning management protocols are warranted.

Previous studies have shown that serum haptoglobin on arrival was increased in steers that required more than one antimicrobial treatment (Carter et al., 2002; Berry et al., 2004). Serum haptoglobin measured on arrival may have potential as a predictor of clinical BRD. A diagnostic tool to identify infection would be useful to producers and veterinarians by providing objectivity to diagnosis. The first objective of this experiment was to determine the effects of commingling calves of unknown backgrounds and sources with calves obtained directly from their ranch of origin but differing in management prior shipping. The second objective was to evaluate serum haptoglobin concentrations as a prognostic indicator of health, treatment outcome, and performance in these cattle.

MATERIALS AND METHODS

Animals
A total of 509 crossbred beef steers (Table 1) were used to study the effects of calf origin and weaning management on animal health and performance. The experiment was conducted at the Willard Sparks Beef Research Center (WSBRC), Stillwater, OK. The steers were either from multiple sources (auction market; MARKET) or a single ranch (RANCH). Auction market origin steers (n = 260) were purchased through a private order buyer who acquired the steers through regular auction-market channels in the southeastern U.S. Steers were assembled at a facility in Mississippi before transporting to the WSBRC, approximately 1,086 km (approximately 11 h transport time). The MARKET cattle did not have known health histories, and thus were considered to be high-risk, exposed cattle (i.e., likely exposure to different respiratory pathogen isolates not indigenous to herds of origin due to commingling that occurred at various facilities before shipment to the WSBRC). To minimize possible sources of variation due to animal management and genetics, RANCH calves (n = 249) were selected from a single ranch in south-central Missouri located approximately 563 km (approximately 6 h transport time) from the WSBRC. Due to the objectives and subsequent design of the experiment (see below), groups of calves arrived at the WSBRC on dates separated by approximately 46 d (Table 1). Average daily temperature, humidity, wind speed, and precipitation in Stillwater, OK from November 2 through December 16, 2002 was 5.57 ± 5.10°C, 75.4 ± 16.1%, 11.6 ± 9.4 km/h, and 0.81 ± 4.38 mm. Average daily temperature, humidity, wind speed, and precipitation in Stillwater, OK from December 18, 2002 through January 31, 2003 was -0.01 ± 5.28°C, 74.1 ± 15.3%, 15.6 ± 9.0 107 km/h, and 0.34 ± 2.06 mm.

Experimental Design

Calves from the ranch were weaned and immediately shipped to the WSBRC (WEAN); weaned on the ranch for 45 d before shipping, but did not receive any vaccinations (WEAN45); or weaned, vaccinated with modified live viral vaccine, and held on the ranch for 45 d before shipping (WEANVAC45). At approximately 2 mo of age (approximately 115 kg), RANCH calves had been castrated, dehorned, and vaccinated with a 7-way Clostridial bacterin/toxoid (brand unknown). The MARKET cattle used in this experiment arrived at the WSBRC on November 2 or December 19 and 21, 2002. As indicated, pre-arrival health management and processing was unknown for MARKET cattle. Although we requested predominantly black Bos taurus crossbred castrated males with similar BW as RANCH steers for this experiment, the shipment of purchased cattle included intact males (n = 3 in November arrival cattle) with some variation in phenotype. After initial processing, a portion of MARKET cattle were commingled with a portion of steers from each weaning management group (COMM). Treatments were arranged in a 2 × 3 + 1 factorial with RANCH vs. COMM and weaning management (WEAN vs. WEAN45 vs. WEANVAC 45) as the factors; MARKET cattle served as the control. The experimental protocol was approved by the Oklahoma State University Institutional Animal Care and Use Committee.

The WEAN steers were simultaneously weaned and shipped to the WSBRC when they were approximately 8 mo of age (November 2, 2002). No other preventive health procedures for BRD were performed on these steers before arrival; hence, these calves were considered high-risk and non-exposed cattle. The WEAN calves were kept isolated f 128 from MARKET cattle on arrival. After arrival, all steers were allowed to rest in clean dry pens at least 1 h before being weighed and individually identified with a bangle tag. After weighing and tagging, steers were allowed to acclimate for approximately 24 h in 12.2 m x 30.5 m pens. Long-stemmed prairie hay and water were provided ad libitum. Approximately 24 h after arrival, initial processing procedures included administration of a modified live viral respiratory vaccine (IBRV-BVDV type 1 & 2-PI3V-BRSV, Titanium 5, AgriLabs, St. Joseph, MO), a 7-way Clostridial bacterin/toxoid (Vision 7 with SPUR, Intervet Inc, Millsboro, DE), a Mannheimia (Pasteurella) haemolytica/toxoid (Presponse SQ, Fort Dodge Laboratories Inc, Fort Dodge, IA), and an endectocide (Ivomec Plus, Merial Ltd., Iselin, NJ) to all WEAN and MARKET steers. In addition, all steers were re-weighed and palpated for testicles. Fourteen days after initial processing, WEAN and MARKET steers were revaccinated with a modified live viral respiratory vaccine in combination with a Leptospira bacterin component (Titanium 5 L5, AgriLabs).

As indicated, WEAN45, and WEANVAC45 steers originated from the same ranch and were weaned November 2, 2002 like the WEAN steers, but were held on the ranch for 45 d before being transported to the WSBRC. At weaning, WEANVAC45 calves were vaccinated with 1 dose each of a modified live viral respiratory vaccine (Titanium 5, AgriLabs), a 7-way Clostridial bacterin/toxoid (Vision 7 with SPUR, Intervet), and a Mannheimia (Pasteurella) haemolytica/toxoid (Presponse SQ, Fort Dodge Laboratories). Two weeks after weaning, WEANVAC45 calves were re-vaccinated with a modified live viral vaccine in combination with a Leptospira bacterin component (Titanium 5 L5, AgriLabs) and categorized as low-risk cattle. The WEAN45 calves were weaned on the ranch for 45 d but were not vaccinated at weaning. These calves were considered to be of unknown-risk. At weaning, calves were randomly assigned to the 3 weaning management groups on the 151 ranch. The WEAN45 and WEANVAC45 steers were weaned in separate tall fescue grass pastures at similar stocking rates. The WEAN45 and WEANVAC45 steers were shipped to the WSBRC in separate trucks on December 18, 2002. Separate truckloads of MARKET calves arrived on December 19 and 21, 2002. The protocol for handling cattle on arrival was the same as for calves arriving in November. Approximately 24 h after arrival, WEAN45 and MARKET cattle were processed using procedures described previously. The WEANVAC45 steers were processed through the chute; however, only the
endectocide was given and no vaccinations were administered. Fourteen days after initial processing, WEAN45 and MARKET steers were revaccinated with a modified live viral respiratory vaccine in combination with a Leptospira bacterin component (Titanium 5 L5, AgriLabs).

For cattle arriving in both November and December, experimental treatments were randomly assigned to 4 adjacent pens (n = 4) within the feedyard, and calves within treatment group were randomly assigned to 1 of the 4 pens. Each treatment group of 4 pens was separated with an empty pen or alley to prevent animal-to-animal exposure among treatments. Pens were 166 12.2 m × 30.5 m with 12.2 m of concrete fence-line bunk. For steers arriving in November, 58 ranch-origin steers (WEAN) were randomly allocated to 4 pens (14 or 15 steers/pen), and 28 ranch-origin steers were randomly allocated to 4 different pens for commingling with MARKET cattle (7 WEAN steers/COMM pen). Sixty-eight MARKET steers were randomly allocated to 4 pens (17 steers/pen), whereas 33 MARKET steers were commingled with WEAN calves in the 4 COMM pens (8 or 9 MARKET calves/pen; 15 or 16 total calves/COMM pen). For steers arriving in December, 52 WEANVAC45 steers were randomly allocated to 4 pens (13 calves/pen), whereas 59 WEAN45 steers were randomly allocated to 4 pens (14 or 15 calves/pen). There were 16 MARKET calves allocated to each of 4 pens (64 total MARKET steers). For the commingling treatments, 29 WEAN45 (7 or 8 calves/pen) and 35 MARKET (8 or 9 calves/pen) steers were commingled into 4 pens (16 total calves/pen). In addition, 23 WEANVAC45 (5 or 6 calves/pen) and 41 MARKET (10 or 11 calves/pen) steers were commingled into 4 pens (16 total calves/pen). For all COMM treatment pens, RANCH steers were placed in the pens first followed by MARKET steers.

The order for the initial and all subsequent processing of calves through the chute remained consistent during both receiving periods (i.e., November and December). The order was implemented to minimize the potential for accidental mixing of treatment groups. Steers received in November were processed on arrival and throughout the experiment in the order of WEAN; MARKET; and commingled WEAN and MARKET. Steers received in December were processed as in the order: WEANVAC45; WEAN45; MARKET; commingled WEANVAC45 and MARKET; and commingled WEAN45 and MARKET.

Diet and Weighing

Following d-0 processing, calves were moved to assigned pens and offered 1% of BW of a diet consisting of (DM basis) 34.7% dry-rolled corn, 25.0% ground alfalfa hay, 27.0% cottonseed hulls, 3.0% cane molasses, and 10.3% pelleted supplement (58.4% soybean meal, 191 29.2% cottonseed meal; 9.7% limestone; 2.3% salt; 0.16% Rumensin 80 [Elanco Animal Health, Greenfield, IN]; 0.18% vitamin A 30,000; 0.04% vitamin E; and 0.01% selenium). Feed was delivered into the feed bunks (12.2 m). Cattle were fed the diet twice daily (approximately 0700 and 1400) to ensure ad libitum intake; half of the calculated ration was fed at each feeding. Prairie hay (1.8 kg/steer on the day of processing) was supplied for the first 7 d of receiving only, and was decreased by 0.23 kg/d as intake of the mixed diet increased. Feed bunks were evaluated at approximately 0630 for remaining feed and feed delivery was adjusted before the 0700 feeding. Inclement weather was the only factor involved in a change in the above described feeding schedule. Feed refused was weighed at 14-d intervals and as needed (e.g., following inclement weather). Dry matter content of pen orts samples was determined in a forced-air oven by drying for 12 h at 100°C. In addition, diets were composited in 14-d increments and DM determinations used to calculate DMI and G:F per pen after correcting for orts. Steers had ad libitum access to water via automatic waterers positioned to supply water to 2 adjacent pens/basin.

Alfa Alfa Hay

Dry Rolled Corn

Cottonseed Hulls

Calves were weighed on d -1, 0, 14, 28, and 42 (0700) of the experiment. All weights with the exception of initial (average of d -1 and 0) and d 42 were shrunk by 4% to calculate daily gain and gain efficiency. On day 41, calves received morning feed only and the water was turned off the previous evening (1700) before weighing.

Clinical Evaluation for BRD

All calves were monitored by 2 experienced evaluators (1 DVM with 25 yr of experience and 1 herdsman with 35 yr of experience identifying morbid cattle) daily throughout the study for clinical signs consistent with BRD. The evaluators used criteria based on the DART system (Pharmacia Upjohn Animal Health, Kalamazoo, MI) with some modifications. Specifically, the subjective criteria used to indicate further evaluation for clinical BRD were depression, appetite, and respiratory signs. Signs of depression included depressed attitude, hanging head, glazed and/or sunken eyes, slow movement, arched back, difficulty getting up from lying down, knuckling or dragging toes when walking, and stumbling when moving (not including being bumped by another animal). Signs of abnormal appetite included completely off feed, eating less than expected, slow eating (when considered different from an animal’s normal behavior), lack of fill (gaunt), and obvious weight loss. Respiratory signs 220 included obvious labored breathing, extended head and neck, and noise when breathing. The evaluators also assigned a severity score of 1 to 4, where 1 was assigned for mild, 2 for moderate, 3 for severe, and 4 for moribund (steer would not rise from recumbency; assistance was needed) during their evaluation. The fourth objective criteria used to determine if antimicrobial therapy was needed on an individual animal basis was rectal temperature. Any animal with a rectal temperature of 40°C or higher received an antimicrobial according to label directions. Before antimicrobial administration, an accurate BW was obtained to calculate the appropriate dosage. In situations where the evaluators assigned a severity score of 3 or 4 to a steer, antimicrobial therapy was administered regardless of the animal’s rectal temperature. If a steer did not meet the subjective severity score and temperature criteria, no antimicrobial therapy was administered. All steers were returned to their home pen after evaluation. Temperature readings, BW, and treatments (or no therapy administered) were recorded for every steer that was examined for clinical signs consistent with BRD. Information was recorded for any animal that required examination for any medical condition, such as digestive disorders, lameness, neurological diseases, etc.

Digestive Disorder

Lameness

Neurological diseases – Blindness

The first treatment administered to steers suffering from clinical BRD was tilmicosin (Micotil 300, Elanco Animal Health, Greenfield, IN) at a dosage rate of 10 mg/kg BW. If steers required a second treatment after 48 h from receiving their first treatment, the antimicrobial used was enrofloxacin (Baytril 100, Bayer Corp, Shawnee Mission, KS) at a dosage rate of 10 mg/kg BW. If a steer required a third antimicrobial treatment after 48 h from receiving their second treatment, the antimicrobial used was ceftiofur HCl (Excenel RTU, Pharmacia Upjohn) at a dosage rate of 2.2 mg/kg BW. The dose of ceftiofur HCl was repeated in 48 h. Any steer that exhibited clinical signs consistent with BRD and meeting criteria for a fourth treatment was deemed to be suffering from a chronic disease process and was removed from the experiment. In addition, any steer that exhibited severe clinical signs was moved to an isolated hospital pen for the remainder of the experiment. Any steer that died or required euthanasia was submitted for a complete post mortem examination at the Oklahoma Animal Disease Diagnostic Laboratory. Beef Quality Assurance Guidelines as recommended by the National Cattlemen’s Beef Association (NCBA, 2001) were followed throughout this study.

Clinical Bovine Respiratory Disease

Haptoglobin and Serology

Blood samples were collected via jugular venipuncture (10 ml Vacutainer tube with no additive; Becton Dickinson, Rutherford, NJ) from all calves on arrival and from steers that were treated for BRD. Blood was allowed to equilibrate to ambient temperature before overnight storage at 4ºC. Serum was separated the following day and stored at -10ºC until laboratory analysis could be conducted. Serum haptoglobin concentrations were determined using Bovine Serum Haptoglobin radial immunodiffusion kits (Code No. P0105-1, Cardiotech Svcs., Inc., Louisville, KY) as described by Berry et al. (2004). The coefficient of variation for the kit was less than 4% for repeated, identical measurements of the same specimen.

Bovine-HP-Haptoglobin Elisa Kit

Serum antibody concentrations to formalin killed Mannheimia haemolytica whole cells (MhWC), leukotoxin (MhLKT) and Pasteurella multocida outer-membrane proteins (PmOMP) were determined by enzyme-linked immunosorbent assay. The ELISA wells were coated with 100 μL of antigen at a concentration of 1 ng/μL of coating buffer for PmOMP. For the MhWC preparation, M. haemolytica A1 obtained from a washed 18-h culture was suspended in 0.4% formalinized saline at a concentration determined spectrophotometrically to be 1.350 OD600. Leukotoxin was prepared from the supernatant of M. haemolytica A1 culture in log phase growth. The MhLKT was partially purified by ammonium sulfate precipitation (Clinkenbeard et al., 1994), confirmed by SDS-PAGE and immunoblotting 266 with an anti-MhLKT antibody, and MhLKT activity of the preparation calculated at 104 MhLKT U/mL (Confer et al., 1998). As a measure of lipopolysaccharide contamination of the MhLKT preparation, the 2-keto-deoxyoctonate concentration was 7.5 μg/mg protein.

Mannheimia haemolytica

Ninety six-well microtiter plates were coated with MhWC at an optical density reading equivalent to 108 CFU of a 24-h culture and MhLKT at 50 ng per well. Sera was tested at 1:400 for PmOMP, 1:800 for MhWC or 1:1600 for MhLKT dilutions in PBS-Tween 20 containing 1% BSA. Antibody binding was detected using a 1:400 dilution of horseradish peroxidase conjugated, affinity purified rabbit anti-bovine IgG (Kirkegaard & Perry Laboratories, Gaithersburg, MD). Antibody responses were reported as nanogram of immunoglobulin binding based upon comparison with a set of IgG standards on each plate.

Carcass Data

After completion of the 42-d receiving period, cattle were transported to a commercial feedlot for finishing. The feedlot was selected by the cooperating producer/owner with retained ownership of the cattle through slaughter. All cattle were fed a commercial high-concentrate finishing diet for approximately 200 d. Cattle were slaughtered at a commercial facility when 60% appeared to grade USDA Choice based upon subjective evaluation of body composition.

Carcass data (HCW, USDA Quality Grade, and USDA Yield Grade) were collected at slaughter.

Calculations and Statistics

Individual health costs per steer were calculated using: $1.00 each time a steer went through the chute; $0.35 per antimicrobial treatment for syringe and needle; $0.97/mL for 1st treatment antimicrobial; $0.46/mL for 2nd treatment antimicrobial; $0.49/mL for 3rd treatment antimicrobial; and $7.63 for vaccines and dewormer for all groups except WEANVAC45, which was $8.02 (administered an additional 1 mL dewormer due to increased a rrival BW). Costs assigned per steer for the calculation of total cost of production per steer included the individual
health cost plus a yardage charge of $0.25/steer daily and the feed cost per pen/number steers per pen. The cost of gain was calculated using the total cost of production divided by ADG over the 42-d period of the experiment.

Receiving performance and health data were analyzed as a 2 × 3 + 1 factorial arrangement of treatments in a completely randomized design using the MIXED procedure of SAS (SAS Inst. Inc. Cary, NC). Pen was used as the experimental unit. Fixed effects included RANCH vs. COMM, three weaning management treatments (WEAN, WEAN45 and WEANVAC45), and MARKET served as the control. When no interaction (commingling x weaning management; P > 0.10) occurred, Least-squares means for main effects are reported. For comparing treatment differences among MARKET and RANCH calves in COMM pens,individual animal was used as the experimental unit. The model included the fixed effects of
calf origin, weaning management, and the calf origin × weaning management interaction. Calf origin × weaning management nested within pen was included as a random effect. Due to arrival BW being greater (P = 0.01) for WEANVAC45 calves compared with MARKET, WEAN, and WEAN45 calves, arrival BW was included in the model as a covariate for all performance, health cost, and carcass data. Analysis was conducted to determine if differences in haptoglobin concentrations could be detected in calves that would never be treated for BRD, calves that would be treated only once for BRD, or calves that would require multiple antimicrobial treatments for BRD. For this analysis, individual animal was used as the experimental unit. The model included fixed effects of number of antimicrobial treatments, weaning management, and the antimicrobial treatments × weaning management interaction. Antimicrobial treatments × weaning management nested within pen was included as a random effect. Least-squares means were compared using LSD when protected by a (P < 0.05) F-test. Regression analysis was conducted using the REG procedure of SAS with number of times treated (0, 1, >1) as the independent variable and haptoglobin concentration as a dependent variable. Results are discussed as significant if P < 0.05 and as tendencies if P > 0.05 to P < 0.10.

RESULTS

Criteria for removing data from a steer used in the experiment included severe respiratory distress, lameness, neurological abnormalities, or death (dead animals were used in the calculation of mortality rates). Fourteen steers were removed from the entire study due to respiratory distress and all were of MARKET origin (2 from November and 12 from December); 8 of the 14 died (1 from November and 7 from December), and the clinical diagnosis of BRD was confirmed on post mortem examination. Fifteen steers were removed from the study due to lameness (5 WEAN, 7 MARKET from November and 3 MARKET from December); all 15 recovered with appropriate therapy. One WEAN steer was removed from the study for treatment of neurological disease; the steer’s condition deteriorated despite treatment and was euthanized. The post mortem diagnosis for the steer was severe bronchopneumonia and a cerebral infarct was observed in the brain.

Animal Performance

There were no commingling x weaning management interactions (P > 0.10) for BW, 332 ADG, or DMI across the 42-d receiving period. Therefore, main effects means for commingling (Table 2) and weaning management (Table 3) are reported. Commingling RANCH- and MARKET-origin calves did not affect (P > 0.15) BW on d 1, 14, or 28 of the receiving period (Table 2). However, BW on d 42 tended (P = 0.06) to be greater 335 for RANCH compared with MARKET and COMM calves. On d 15 through 28, ADG was greatest (P = 0.03) for RANCH calves, intermediate for COMM calves, and least for MARKET calves. In addition, from d 1 through 42, ADG tended (P = 0.06) to be greater for RANCH compared with MARKET and COMM calves. Dry matter intake did not differ (P > 0.16) among calf origins. Similarly, DMI expressed as a percentage of BW did not differ (P > 0.13) among calf origins, averaging 2.51 ± 0.05% of BW across the 42-d receiving period. From d 1 through 14 there was a commingling × weaning management interaction (P = 0.03) for G:F (data not shown). Calves weaned on the ranch for 45 d (WEAN45 and WEANVAC45) had lower G:F than WEAN calves when calves were not commingled. However, when commingled, WEAN45 and WEANVAC45 calves had similar G:F compared with WEAN calves. A similar interaction (P = 0.03) occurred from d 1 through 42 (data not shown). From d 15 through 28, G:F was greatest (P = 0.03) for RANCH calves, intermediate for COMM calves, and least for MARKET calves (Table 2). However, across the receiving period (d 1 through 42), G:F did not differ (P = 0.11) among calf origins. Effects of weaning management are shown in Table 3. On arrival, calves in the WEANVAC45 treatment had greater (P = 0.01) BW than MARKET, WEAN, and WEAN45 calves; therefore, arrival BW was used as a covariate in the statistical analysis. On d 28, BW was greater (P = 0.02) for WEAN compared with MARKET, WEAN45, and WEANVAC45 calves. No other differences (P > 0.24) in BW were observed. From d 1 through 14 (P = 0.24) and d 1 through 42 (P = 0.46), ADG did not differ among weaning management treatments.
However, ADG was greater (P = 0.005) for WEAN and WEANVAC45 than MARKET calves from d 15 through 28; WEAN45 had lower ADG than WEAN calves, and similar ADG compared with WEANVAC45 calves during the same period. From d 29 through 42, MARKET, WEAN45, and WEANVAC45 calves had gr 358 eater (P < 0.001) ADG than WEAN
359 calves. Calves on the WEAN45 and WEANVAC45 treatments had similar ADG, but WEAN45 calves had greater ADG than MARKET calves. From d 1 through 14, DMI expressed as kg/d or as a percentage of BW was greater (P < 0.002) for WEAN45 and WEANVAC45 than WEAN and MARKET calves. Dry matter intake expressed as kg/d or as a percentage of BW was greater (P < 0.003) for MARKET, WEAN45, and WEANVAC45 than WEAN calves from d 29 to 42. Similarly, DMI expressed as a percentage of BW was greater (P < 0.001) for MARKET, WEAN45, and WEANVAC45 than WEAN calves across the 42-d receiving period. Gain efficiency was greater (P = 0.01) for MARKET and WEAN than for WEAN45 and WEANVAC45 calves from d 1 through 14. From d 15 through 28, G:F was greatest (P = 0.003) for WEAN, followed by WEANVAC45, WEAN45, and MARKET. From d 29 through 42, WEAN calves had lower (P = 0.001) G:F than calves on the remaining treatments. However, G:F did not differ (P = 0.17) among weaning protocols across the 42-d receiving period. We determined the effects of calf-origin and weaning management on ADG of steers in commingled pens (data not shown). There were no calf-origin x weaning management interactions (P > 0.10) for ADG. Calf origin did not affect (P > 0.10) ADG in commingled pens. Interestingly, similar to calves that were not commingled, weaning management did not affect ADG from d 1 through 14 (P = 0.89), d 15 through 28 (P = 0.30) or d 1 through 42 (P = 0.45). However, from d 29 through 42, WEAN45 (1.91 kg/d) and WEANVAC45 (1.76 kg/d) had
greater (P = 0.03) ADG than WEAN (1.22 kg/d) calves.

Table 2

Table 3

Animal Health

Serum haptoglobin concentrations and antibody titers to M. haemolytica and P. multocida in steers on arrival are shown in Table 4. On arrival, serum haptoglobin concentrations were greater (P < 0.001) in MARKET and WEAN calves compared with WEAN45 and WEANVAC45 calves. Whole cells of M. haemolytica were different (P < 0.001) among treatments WEAN<MARKET<WEAN45<WEANVAC45). Mannheimia haemolytica
leukotoxin and PmOMP were greater (P < 0.001) in WEAN45 and WEANVAC45 calves than MARKET and WEAN calves.

Table 4

There were no commingling x weaning management interactions (P > 0.10) for animal health response variables across the 42-d receiving period (data not shown); therefore, main effects means for calf origin and commingling (Table 5) and weaning management (Table 6) are reported. Percent morbidity differed (P < 0.001) among calf origins (Table 5). A greater (P < 390 0.04) percentage of MARKET calves required 3 antimicrobial treatments compared with RANCH or COMM calves. Calves receiving MARKET and COMM treatments received their
first antimicrobial treatment earlier (P < 0.001; d 7 and 11, respectively) than RANCH calves (d 18). However, during the first antimicrobial treatment, serum haptoglobin, MhWC, MhLKT, and PmOMP did not differ (P > 0.10) among calf origins.

Table 5

Table 6

Calves on the MARKET treatment received their second antimicrobial treatment on approximately d 9 compared with d 22 to 23 for RANCH and COMM calves, respectively (P = 0.007; Table 5). Serum haptoglobin concentration tended (P = 0.09) to be greater for MARKET and COMM compared with RANCH calves during the second antimicrobial treatment. During the second antimicrobial treatments, MhWC and PmOMP did not differ (P > 0.10) among treatments. However, MhLKT concentration (P = 0.04) was greater in COMM calves compared with RANCH or MARKET calves. Commingling did not affect (P = 0.37) the day of the third antimicrobial treatment. In addition, haptoglobin, MhWC, MhLKT, and PmOMP did not differ (P > 0.10) among treatments during the third antimicrobial treatment. Mortality due to BRD was greater (P = 0.03) in MARKET and COMM than RANCH calves. 404 In addition, health costs and total costs were greater (P < 0.02) in MARKET and COMM compared with RANCH calves; cost of gain did not differ (P = 0.22) among calf-origin treatments.

Effects of weaning management on morbidity, mortality, and health costs are shown in Table 6. Total percent morbidity and percentage of calves treated once was greater (P < 0.001) in MARKET and WEAN calves compared with WEAN45 and WEANVAC45 calves. Calves on MARKET treatment were pulled and treated earlier (P = 0.004) in the receiving period than WEAN and WEAN45 calves; WEANVAC45 calves were intermediate. The percentage of calves treated twice was greater (P = 0.05) for WEAN compared with WEAN45 and WEANVAC45, whereas percentage of calves treated 3 times was greater (P = 0.02) for MARKET compared with WEAN45 and WEANVAC45. Weaning management did not affect (P > 0.10) haptoglobin, MhWC or MhLKT; however, PmOMP was greater (P = 0.01) in WEAN45 and WEANVAC45 compared with WEAN calves, whereas MARKET calves were intermediate.

Similar to the first day of antimicrobial treatment, MARKET calves were pulled and treated earlier (P = 0.01) for their second antimicrobial treatment than WEAN and WEAN45 calves, and WEANVAC45 calves were intermediate (Table 6). Concentrations of haptoglobin and MhWC did not differ (P > 0.10) among weaning management treatments. However, during the second antimicrobial treatment MhLKT and PmOMP were greater (P = 0.01) in WEAN45 calves than MARKET or WEAN calves. There were no differences (P > 0.10) in days, haptoglobin, or antibody concentrations among weaning management treatments during the third antimicrobial treatment. Mortality did not differ (P = 0.50) among treatments. Health costs were greater (P < 0.001) for MARKET and WEAN steers than WEAN45 or WEANVAC45 steers. Total costs were greater (P = 0.009) for MARKET 427 than WEAN, WEAN45, and WEANVAC45
steers. Cost of gain tended (P = 0.07) to be greater for MARKET and WEAN than for WEAN45 and WEANVAC45 calves.

The effects of calf origin and weaning management on morbidity, mortality, and health
costs of steers in commingled pens are shown in Table 7. There were no calf origin x weaning management interactions (P > 0.10; data not shown); therefore, main effects are reported. In commingled pens, there tended (P = 0.06) to be more MARKET steers treated once than RANCH steers. In addition, day of first treatment averaged 8.5 for MARKET versus 15.4 for RANCH (P = 0.02). No other effects due to calf origin (P > 0.10) were observed. Within commingled pens, effects due to weaning management were generally similar to steers that were not commingled. A greater percentage of WEAN calves than WEAN45 or WEANVAC45 calves were treated once (P < 0.001) or twice (P = 0.01). During the first antimicrobial treatment, antibody titers to P. multocida tended (P = 0.08) to be greater for WEAN45 and WEANVAC45 compared with WEAN steers. In addition, health costs were greater (P = 0.05) for WEAN than for WEAN45 and WEANVAC45 calves.

Table 7

Arrival serum haptoglobin concentrations for calves that were never treated for BRD
443 were greater (P < 0.001) for MARKET and WEAN than for WEAN45 and WEANVAC45 calves (240.1, 241.6, 82.3, and 93.7 ± 29.6 ug/mL, respectively). In addition, arrival haptoglobin concentration increased (P = 0.05) as the number of antimicrobial treatments increased (164.4, 229.1, and 317.3 ± 77.2 ug/mL for calves treated 0, 1, or > 1 times, respectively). However, regression analysis showed that the relationship between arrival serum haptoglobin and number of antimicrobial treatments was poor [Antimicrobial treatments = 0.197 (± 0.032) + 0.0005 (± 0.0001)*[Hp, μg/mL]; (r2 = 0.06; P < 0.001).

Carcass Data

Calf origin and commingling did not affect (P > 0.10) HCW or USDA Quality Grade
(data not shown). United States Department of Agriculture Yield Grade was greater (P < 0.001) for RANCH (2.61) compared with MARKET (1.97) and COMM (2.28) steers. The effects of weaning management on carcass merit are shown in Table 8. Hot carcass weight and USDA Quality Grade did not differ (P > 0.18) among treatments. However, USDA Yield Grade was greater (P < 0.001) for WEAN steers than for WEAN45 and WEANVAC45 steers, which had greater Yield Grades than MARKET steers.

Table 8

DISCUSSION

Steers weaned, vaccinated, and held on the ranch for 45 d were heavier than other
treatment groups on arrival (Table 3). Steers were handled in a similar fashion and housed similarly on the ranch to minimize processing and facility variations. Although we attempted to minimize variation by including ranch source steers from a single ranch, factors such as genetic variation, forage quality and intake, physical comfort to cattle, among other unknown factors cannot be ruled out as potential reasons for this difference. In addition, the present data may suggest that including a vaccination program during the 45-d weaning period on the ranch of origin resulted in increased BW. For example, Schunicht et al. (2003) and MacGregor and Wray (2004) have reported an improvement in cattle performance when multiple viral antigen vaccines were used. In the present experiment, due to this difference among WEANVAC45 and WEAN45 calves, arrival BW was included as a covariate in the statistical models in an attempt to remove this source of variation.

The purpose of preconditioning programs is to decrease the incidence of BRD from weaning to slaughter by ensuring that calves have been weaned for 30 to 45 d, vaccinated (clostridial and viral vaccines), treated with anthelmintic, castrated, dehorned, and accustomed to feed bunks and water troughs before being transported to the feedlot (King et al., 2006; Duff and Galyean, 2007). In general, the importance of animal performance in the 45-d preconditioning period might be of secondary importance compared with improving animal health, although improved performance by preconditioned calves might be expected across the entire finishing phase. In the present experiment, RANCH steers that were not commingled with MARKET steers tended to have greater ADG than COMM steers, whereas ADG of MARKET and COMM steers was similar (Table 2). The tendency towards greater ADG in non-commingled RANCH steers may be attributed to differences in genetic potential, less stress due to social interactions, less transport stress, less subclinical disease caused by potential pathogen exposure or yet to be identified factors (Galyean et al., 1999; Duff and Galyean, 2007). Although differences in ADG were noted among weaning management treatments at various periods within the 42-d receiving period, differences did not carry through the entire trial (d 1 to 42; Table 3). In addition, in the present experiment ADG within commingled pens generally ranked similarly to ADG in non commingled pens with the exception of RANCH steers that were weaned and immediately shipped to the WSBRC. Average daily gain of these commingled steers was 1.18 kg vs. 1.29 kg for weaned, ranch-origin steers immediately shipped to the WSBRC that were not commingled. Although a direct comparison cannot be made from the present experiment, this may imply greater stress for RANCH calves that are weaned, transported, and commingled compared with RANCH calves that are preconditioned, transported, and commingled compared with RANCH calves that are preconditioned, transported, and commingled at a receiving or finishing facility.

Hutcheson and Cole (1986) summarized research which suggested that DMI of newly arrived calves which are healthy should average 1.55% of BW from d 0 to 7 following arrival and approximately 1.90% of BW from d 0 to 14 (NRC, 1996). In the present experiment, DMI as a percentage of arrival BW averaged 2.21% from d 1 to 14, and was not different among calf origin treatments (Table 2). Therefore, DMI was greater for calves in the present experiment than DMI suggested by NRC (1996) for stressed calves. Greater DMI (% of BW) for WEAN45 and WEANVAC45 during the first 14 d, and greater DMI (% of BW) for WEAN45 and WEANVAC45 across the receiving period (Table 3) might suggest that previously weaned calves are less influenced by transport and other stressors during shipment to a feedyard. Similarly, Boyles et al. (2007) reported greater DMI for steer calves that were preconditioned for 30 d before shipment to a receiving facility vs. steers that were weaned immediately before shipping. However, in their experiment, preconditioning in a drylot did not improve morbidity compared with calves that were weaned and immediately shipped.

As generally perceived, MARKET steers exhibited higher morbidity rates than ranch origin steers and those in commingled pens exhibited intermediate morbidity rates. Within commingled pens, MARKET steers had greater morbidity than RANCH steers. Additionally, days to first treatment for clinical respiratory disease were earlier in MARKET steers in commingled pens than for RANCH steers. Roeber et al. (2001) conducted an experiment to evaluate effects of morbidity on feedlot performance and carcass traits. In their experiment, preconditioned calves had fewer hospital visits than calves that were purchased at auction markets, similar to the present experiment. In the present experiment, steers weaned on the ranch (WEAN45, WEANVAC45) exhibited less morbidity than MARKET and WEAN steers. This difference influenced health care cost per steer (average = $13.39/steer for MARKET and WEAN vs. $8.62/steer for WEAN45 and WEANVAC45). Therefore, t 518 here was an economic benefit to weaning on the ranch of origin for 45 d. King et al. (2006) reported that price premiums for calves in intensive certified health programs ranged from $2.74/45.45 kg to $7.91/45.45 kg from 1995 to 2004.

In the present experiment, weaning on the ranch for 45 d had a profound effect on measured serum proteins on arrival. Serum haptoglobin concentrations were greater in MARKET and WEAN steers than for preconditioned steers. In addition, serum antibody titers to bacterial respiratory pathogens were significantly increased in steers weaned on the ranch for 45 d. Lower serum haptoglobin and higher serum titers to the bacterial pathogens corresponded to lower morbidity, mortality, and health costs in steers in the present experiment. Similar to previous studies (Carter et al., 2002; Berry et al., 2004), arrival haptoglobin was increased in steers that required more than one antimicrobial treatment. However, the relationship between serum haptoglobin measured on arrival and number of antimicrobial treatments required was poor in the present experiment, leaving its potential as a prediction marker of clinical BRD in question. Nonetheless, weaning cattle for 45 d on the ranch of origin resulted in a lower morbidity and haptoglobin concentrations compared with weaning and immediately shipping calves, or purchasing MARKET calves, regardless of vaccination protocol on the ranch. Minimizing stress is commonly discussed in dealing with many animal health production diseases (Galyean et al., 1999). One way of minimizing the incidence of BRD is to precondition weaned beef cattle. There are many preconditioning programs, but most will include vaccinations against common respiratory pathogens and weaning for greater than 30 d before shipping to the feedlot. In the present experiment, weaning on the ranch for 45 d resulted in healthier cattle.

Weaning calves on the ranch for 45 d (i.e., preconditioning) before transporting to a receiving facility results in improved health and performance during the subsequent receiving and feeding period compared with weaning and transporting calves immediately, or purchasing calves of high health risk. In the present experiment, weaning alone had similar benefits as weaning and vaccination for calves held on the ranch of origin for 45 d. In addition, commingling preconditioned calves has less potential negative effects than commingling calves that are weaned and immediately transported to a feedyard.

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