Abstract
The objective of this study was to evaluate animal health status at entry to a feedlot against feedlot performance and carcass value. There were 24 herds represented by 417 calves in a retained ownership program. The health status at entry was represented by the levels of serum antibody to infectious bovine rhinotracheitis virus (IBRV), bovine viral diarrhea viruses 1 and 2 (BVDV1a, BVDV2), parainfluenza 3 virus (PI3V), bovine respiratory syncytial virus (BRSV), Mannheimia haemolytica, and Pasteurella multocida, as well as by the presence of virus in nasal swabs and blood leukocytes and the presence of bacteria in nasal swabs. The presence or absence of viruses or bacteria at entry did not predict subsequent illness. However, there were predictors of illness severity (number of treatments) and performance parameters of feedlot performance. Herds with a low morbidity rate had higher levels of BVDV1a antibodies than herds with a high morbidity rate. On both an individual-animal and a herd-average basis, calves with low levels of antibody to BVDV1a and BVDV2 had increased total treatment costs. Also, for individual animals and the herd as a whole, low levels of antibody to P. multocida, BVDV1a, and BVDV2 were related to decreased net value to owner (carcass value minus total feedlot cost). Calves treated twice or more had lower levels of antibody to BVDV1a than those treated once or not at all. Differences in herd morbidity rate and treatment costs were more related to appropriate timing of vaccine (last dose at or near delivery of calf) or lack of a 2nd dose of killed vaccine. This was best illustrated by the levels of antibody to BVDV1a. The results of this study were used to formulate recommendations for the subsequent year.
Introduction
Bovine respiratory diseases (BRDs) have an important and serious impact on the beef cattle industry, both for stocker and for feedlot entities. Two excellent reviews have been published on the economic impact and management considerations for minimizing those losses (1,2). Economic losses result from death, decreased performance of diseased cattle, lowered weight gain, increased cost of gain, reduced carcass value, and treatment costs.
Numerous attempts have been made to reduce the impact of BRDs through management practices, including preconditioning programs. These programs are designed to prepare a weaned calf for the “stresses” that may occur when it (1) is commingled with cattle from others sources, of unknown health status; (2) is placed in an environment that maximizes exposure to infectious pathogens; (3) has a compromised immune system and cannot adequately protect itself against pathogens; and (4) is placed in environmental conditions that contribute to disease (temperature changes, dust, transportation, crowding, etc.). Preconditioning programs usually require weaning of calves 30 to 45 d before shipment, dehorning, anthelmintic treatment, vaccinations, and good nutrition. Vaccinations are often the hallmark of preconditioning programs, but, unfortunately, documentation of the efficacy of BRD vaccines in the field is limited (3).
Marketing of North American beef cattle has traditionally been through sale from ranches or farms through order buyers, with the commingled cattle sent to feedlots for finishing. In recent years, retained ownership programs (ROPs) have been advocated so that ranchers can gain increased return on the performance of their cattle, both by capturing genetic potential and by using preconditioning programs to ensure a healthy calf. The ROP of the Noble Foundation (NF) Agricultural Division, Ardmore, Oklahoma, is designed for its educational value. Ranchers learn how their calves perform compared with industry norms, information that allows them to make better breeding and management decisions. The ROP requires that, before delivery, the ranchers precondition their cattle, which includes weaning at least 45 d prior to delivery, castration of males, and dehorning of calves. The recommended vaccination program includes 2 doses of viral vaccines and clostridial vaccination. Anthelmintic treatment is also recommended. However, individual rancher decisions are acknowledged, and vaccinations vary with management strategies and veterinarians' counsel.
The objective of our study was to assess preconditioning programs, including vaccinations, by determining the association between animal health status at shipment to a feedlot with subsequent feedlot performance and carcass evaluation. Serum was assayed for antibodies to 5 viruses [infectious bovine rhinotracheitis virus (IBRV), also known as bovine herpesvirus-1 (BHV-1); bovine viral diarrhea viruses 1 and 2 (BVDV1a and BVDV2); parainfluenza 3 virus (PI3V); and bovine respiratory syncytial virus (BRSV)] and 2 bacteria (Mannheimia haemolytica and Pasteurella multocida). The presence of viruses and bacteria in nasal swabs and of BVDV in peripheral blood leukocytes (PBLs) at the time of shipment was also examined. Upon completion of the feedlot period and processing, numerous economic parameters from the feedlot and carcass information were analyzed against animal health status at shipment.
Materials and methods
Delivery of cattle
There were 24 herds with 417 calves from southern Oklahoma and north-central Texas participating in the 2000–2001 NF ROP. Guidelines included that vaccinations and anthelmintic administration had to be completed prior to delivery to the NF Coffey Ranch, Marietta, Oklahoma. The calves were delivered November 8 to 10, 2000, for processing, which included weighing, identification, and sample collection. Samples included nasal swabs for viral and bacterial isolation, an EDTA blood sample for BVDV isolation from PBLs, and clotted blood samples for serum to be tested for viral and bacterial antibodies. The owners provided a herd health history, including weaning date, vaccines used, vaccination dates for all calves, anthelmintic used, and annual herd vaccinations. The calves were then shipped to a western Oklahoma feedlot, near Guymon, a distance of approximately 380 mi (about 600 km).
During processing at the feedlot, the calves received a vaccine containing modified live virus (MLV) IBRV, BVDV1a, and PI3V, as well as killed BRSV (Reliant 4; Merial Ltd., Iselin, New Jersey, USA). The normal pull-and-treat regimen for the feedlot was followed. An animal was pulled from the pen for respiratory disease when 1 or more of the following signs was present: depression, nasal discharge, lack of rumen fill, and lethargy. If the rectal temperature was less than 104°F (40°C), the calf was called a “respiratory observe”, given an MLV IBRV vaccine, and sent to a hospital observation pen. Calves with a rectal temperature of 104°F or more were treated with a standard antibiotic regimen and sent to a hospital observation pen. Cattle entering a sick pen had the same samples collected as at delivery. Calves that died during the study were necropsied, and tissues were collected for histopathologic study and viral/bacterial isolation. Numerous performance data were obtained from the cattle at delivery and during the feeding period, as was the carcass value and grade (Table I).
Table I.
Virologic, bacteriologic, and serologic studies
Blood samples and nasal swabs were submitted to the Oklahoma Animal Disease Diagnostic Laboratory, Stillwater, Oklahoma, for viral and bacterial isolation. A microtiter virus neutralization test was used to assay for BVDV1a, BVDV2, PI3V, and BRSV antibodies; a plaque reduction assay was used to measure the level of IBRV antibodies (4). Levels of antibodies to M. haemolytica whole-cell antigen, M. haemolytica leukotoxin, and P. multocida outer-membrane protein were measured by enzyme-linked immunosorbent assay (5,6,7).
Statistical analysis
All data were analyzed using SAS software, version 8.2 (SAS Institute, Cary, North Carolina, USA). The relationships of morbidity and mortality to herd were inspected with contingency tables and chi-squared tests using PROC FREQ in SAS. Percentages of calves that were sick or died were compared overall and pairwise to determine which herds differed. Serologic data were analyzed with analysis of variance (ANOVA) on a per-animal basis with PROC MIXED in SAS. Comparisons for levels of the fixed-factor herd were made with a least significant difference procedure, using an LSMEANS statement and a DIFF option. Each serologic variable was used as a response to the treatment variable herd. Correlations of performance parameters with serologic data were calculated on both a herd and an animal basis, using PROC CORR. The relationship of individual-animal health, as judged with a binary response (i.e., sick vs not sick), to antibody titers was analyzed by logistic regression, with PROC LOGISTIC. Finally, the relationship of the performance parameters to the number of treatments (0, 1, 2, or more than 2) was investigated by ANOVA, with PROC MIXED.
Results
Vaccination history
The vaccination histories indicated a variety of viral and bacterial immunogens (Table II). The vaccines and the immunogen components are listed in Table III. Of the 24 herds, 10 received killed-virus vaccines (including chemically altered MLV vaccines against IBRV and PI3V), 9 received MLV vaccines, and 5 received a combination of killed and MLV vaccines. The viral vaccines all contained IBRV, BVDV1a, PI3V, and BRSV. Seven herds received vaccines containing BVDV2 in addition to BVDV1a. Ten herds received M. haemolytica and, or, P. multocida vaccines.
Table II.
Table III.
Morbidity and mortality
Of the 417 calves, 114 (27.3%) were treated and 4 (0.96%) died (Table IV); 3 calves died with signs of respiratory disease and lesions of pneumonia, and the 4th was diagnosed clinically with enterotoxemia. Two calves were sold as “realizers”: they were sold before optimum market time, with conditions that permitted processing and passage of inspection (antemortem and postprocessing). Herds 1, 2, and 12 had a significantly lower morbidity rate (P < 0.05) than herds 3, 13, and 17. Herds 7, 11, 18, and 24 had a significantly lower morbidity rate (P < 0.05) than herd 13.
Table IV.
Bacterial and viral isolation
At entry into the ROP, 115 (27.6%) of the 417 calves had M. haemolytica, P. multocida, or H. somnus isolated from the nasal swabs: 71 (17.0%) had M. haemolytica, 35 (8.4%) had P. multocida, 6 (1.4%) had both M. haemolytica and P. multocida, 2 (0.5%) had atypical M. haemolytica, and 1 (0.2%) had H. somnus. Only 2 herds, nos. 3 and 7, did not have any cattle that were positive for any of these bacteria. M. haemolytica was isolated from the lungs of 1 of the 3 animals that died of pneumonia, a severe, chronic, suppurative bronchopneumonia. Nasal swabs were collected from 107 of the 114 sick animals for bacterial and viral isolation; 22 (20.6%) were culture positive, 17 with M. haemolytica, 4 with P. multocida, and 1 with both bacteria.
No animals were persistently infected with BVDV. At entry, 33 of the 417 (7.9%) had PI3V isolated from the nasal swabs; this virus was isolated from the nasal swabs of only 5 of the 107 sick animals tested. No other viruses were isolated from the nasal swabs at entry, from calves in the sick pen, or from lungs at necropsy.
The presence of virus or bacteria in the nasal swabs at entry did not predict illness or performance parameters.
Serologic findings
The mean titers of antibody to the 5 viral and 3 bacterial antigens were compared among the 24 herds; the bacterial titers were expressed as arithmetic means and the viral titers as geometric means (Table V). There were numerous significant differences for each antigen. For selected herds and antigens, lower titers occurred in several herds with a high morbidity rate, whereas high titers occurred in several herds with lower morbidity rates. This is illustrated with BVDV1a: for the 3 herds with the least illness, nos. 1, 2, and 12, the mean levels were 192, 406, and 50; for the 3 herds with the highest morbidity rates, nos. 3, 13, and 17, the mean levels were 0, 5, and 2.
Table V.
Animal health at entry vs subsequent performance
On an individual-animal basis, there were no significant relationships between health status at entry and sickness (1 or more treatments), although the relationship with low BVDV1a titer approached significance (P = 0.0702). There were, however, numerous significant relationships between health status at entry and performance parameters for both individual animals and herds (Table VI).
Table VI.
The net value to the owner (carcass value – total costs in feedlot) on a herd basis was $365 to $677 per calf (Table VII). Profitability was lowered with treatment. Compared with the calves that were not treated, the calves receiving 1 treatment returned $40.64 less, those receiving 2 treatments returned $58.35 less, and those receiving 3 or more treatments returned $291.93 less (P < 0.05). There were 10 carcass grades: prime −, choice +, choice, choice −, select +, select, select −, standard +, standard, and standard −. Calves treated 2 or more times had lower carcass grades than those not treated or treated only once (P < 0.05). The total treatment costs per animal for each herd ranged from zero (in herd 2) to $21.70 (in herd 3) and differed significantly among the herds (Table VIII).
Table VII.
Table VIII.
The levels of antibody to BVDV1a and BVDV2 predicted illness severity in terms of the number of treatments per sick calf: with BVDV1a, the calves not treated had a mean titer of 78.5, and those treated once had a mean titer of 74.2; in contrast, those treated twice or more had a mean titer of 22.4, significantly lower than the other 2 means (P < 0.05). Likewise, BVDV2 antibody levels approached significance as predictors of illness severity: calves not treated had a mean titer of 16.6, and those treated only once had a mean titer of 18.4, whereas those treated twice or more had a mean titer of 5.7 (P = 0.0633).
Discussion
This study investigated the health status of calves at feedlot entry, based on levels of antibody to several pathogens and the presence of pathogens in nasal swabs and PBLs, against performance during feeding and carcass value and grade. Sampling after feedlot entry was limited to sick cattle, as the study followed normal feedlot protocols, and the cattle were continually owned by participating ranchers. Thus, production losses due to repeated sample collection from all cattle were minimized. All cattle received the normal feedlot vaccines at entry for BRD control. The serologic findings in the sick calves are not reported, as there were no unvaccinated controls.
Analysis of the level of serum antibodies to various infectious agents for their prediction of several performance parameters and carcass information was especially rewarding. Even though on an individual-animal basis there were no significant predictors of illness, a low BVDV1a titer approached significance (P = 0.0702). In multiple instances, low levels of antibody to 4 infectious agents — BVDV1a, BVDV2, P. multocida, and PI3V — predicted performance in several categories. On both a herd and an individual-animal basis, low BVDV1a and BVDV2 titers were related to increased total treatment costs. On both bases, low titers of antibody to P. multocida, BVDV1a, and BVDV2 decreased the net value to the owner (carcass value — total feedlot costs), which reduced the profitability for the rancher of feeding the cattle rather than marketing them at weaning. Low BVDV1a and BVDV2 titers also predicted the number of treatments for the sick calves. In other selected areas, low levels of PI3V antibodies adversely affected feedlot performance.
In general, the economic effects of disease were demonstrated in this study. Animals treated 1 or more times had a reduced average daily gain in the feedlot. Calves treated once or more returned less net value to the owner.
We had planned to identify pathogens in the healthy calves at entry. We expected to isolate viruses or bacteria from the nasal area as well as find acute or persistent BVDV infections. No calves with persistent BVDV infection were identified. It is possible that there was not a severe challenge by naturally occurring pathogens during the feedlot period, as the presence of viruses or bacteria in nasal swabs did not predict illness.
The vaccination regimens used by the 24 ranchers differed, particularly in the number of vaccinations and the timing of vaccine administration. The use of a particular vaccine may not have guaranteed a high level of antibody to the immunogens present: the 3 herds with the highest morbidity rates (nos. 3, 13, and 17) received killed-virus vaccines, of which the 2nd dose was either lacking or given at delivery or 2 d before delivery; their levels of antibody to BVDV1a were significantly lower than the levels in the 3 herds with the lowest morbidity rates (nos. 1, 2, and 12).
The 3 herds with the highest morbidity rates also had much different schedules of administration: herd 3 received a killed-virus vaccine with 4 viruses (IBRV, BVDV1a, PI3V, and BRSV) approximately 3 wk before and again only 2 d before delivery; herd 13 received only 1 dose of a killed-virus vaccine with the same 4 viruses approximately 13 wk before delivery; and herd 17 received a killed-virus vaccine with the same 4 viruses plus BVDV2 and a P. multocida/M. haemolytica product approximately 3 wk before and the day before delivery. In contrast, the timing of vaccine administration in the herds with the lowest morbidity rates was more alike: herd 1 received an MLV vaccine with the same 4 viruses approximately 7 and 3 wk before delivery; herd 2 received an MLV vaccine with the same 4 viruses approximately 7 wk before delivery; and herd 12 received a killed-virus vaccine with the same 4 viruses plus an M. haemolytica product approximately 6 and 4 wk before delivery.
The mean treatment costs per animal, by herd, ranged from zero to $21.70. Of the 4 herds with significantly higher treatment costs than 8 other herds, 3 were the herds with the highest morbidity rates. The 4th herd (no. 14) also had a high morbidity rate, and its vaccination regimen appeared to meet expectations: a nasal MLV vaccine with IBRV and PI3V was given approximately 6 wk prior to delivery, an MLV vaccine with the basic 4 viruses was given approximately 6 and 3 wk before delivery, and an M. haemolytica product was given 3 wk before delivery. Although the presence of bacteria in the nasal swabs did not predict illness for the calves in this study, herd 14 was unusual in that 4 of the 5 calves had M. haemolytica (2), P. multocida (1), or both (1) in the nasal swabs.
This study demonstrated the association between performance parameters in the feedlot and low levels of serum antibodies to certain pathogens in the cattle upon entry to the feedlot. Interestingly, in other studies, high titers of antibody to BVDV have been found to protect against undifferentiated BRD (8,9,10,11). In a recent study, in which the majority of animals were vaccinated against BVDV at arrival, those treated for undifferentiated BRD had larger increases in the titer of antibody to BVDV than the non- treated animals (11). The low P. multocida antibody titers in our study were noteworthy. Most bacterial biologics for BRD have stressed M. haemolytica. With the economic effects related to P. multocida shown in this study, it is now important to develop efficacious P. multocida vaccines.
In summary, this study attempted to determine whether certain vaccinations in the preconditioning phase of an ROP enhance protection against BRD and provide economic benefit. We used the levels of antibody to 5 viruses and 2 bacteria involved in BRD to demonstrate these relationships. Admittedly, there were herds with low numbers of animals, yet statistical analysis demonstrated many definitive relationships. Serum antibodies to certain pathogens detected at entry to the feedlot were related to feedlot performance in the 417 cattle from 24 herds, all in some form of a preconditioning program that included vaccinations.
Footnotes
Acknowledgments
This work was supported by a research grant from The Noble Foundation, Ardmore, Oklahoma. We gratefully acknowledge the staff of the NF Agricultural Division for processing the cattle and for data collection and the staff of the Hitch Feedlots, Guymon, Oklahoma, for sample collection. The typing assistance of Ms. Diana Moffeit was greatly appreciated.
Address correspondence and reprint requests to Dr. Robert W. Fulton, Department of Veterinary Pathobiology, Room 250, McElroy Hall, College of Veterinary Medicine, Oklahoma State University, Stillwater, Oklahoma 74078 USA, tel: 405-744-8170, fax: 405-744-5275, e-mail: rfulton@okstate.edu
Received October 19, 2001. Accepted March 5, 2002.
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