The factors that leave feedlot calves at high risk for bovine respiratory disease complex, or BRDC, have been studied and are fairly well understood. However, no large-scale studies have been reported that investigate the management factors that could be associated with higher rates of BRDC in preweaned calves in cow/calf operations. So, Kansas researchers drew from the extensive real-world data collected during USDA’s regular National Animal Health Monitoring System surveys of beef producers. USDA’s Beef 2007–2008 study generated data both on management factors and on the rate of disease occurrences for cow/calf herds. The Kansas State study used those data to provide a unique assessment of potential statistical associations between cow/calf herd management practices and the rate of BRDC in preweaned calves.
The study, published in the May 1 issue of the Journal of the American Veterinary Medical Association, surveyed a total of 443 beef operations from an initial pool off 4,001 producers contacted to participate, based on their willingness to respond and whether they had any calves on the operation any longer and could give them feedback on BRDC. The median number of beef cows on the 443 operations was 128, with a range of from two to 5,847. The study authors used a sophisticated statistical model to try to account for the impact of several variables at once and to predict the chances of BRDC occurring based on those variables.
They found several management factors did not significantly predict whether pre-weaning calves on an operation would have BRDC--some of which do not square with conventional wisdom. They were:
- Herd size.
- The proportion of cows under 5 years old.
- How often sick cows were housed in the calving pen.
- Vaccination of calves between 22 days old and weaning with a 4-way viral vaccine.
- Whether a veterinarian had been consultation with the herd manager about disease prevention.
- The number of specifically defined breeding seasons.
- Separating cow/calf pairs from pregnant cows.
- Average number of days from birth to dehorning.
- Creep feeding.
- AI-ing cows.
- Body condition scoring.
The final multivariable model included 6 independent variables that were found to be significantly associated with herd-level BRDC rates. They were:
Feeding antibiotic feed additives to calves to prevent respiratory disease was associated with higher rates of BRDC. You have to careful about evaluating what this association means, the study authors cautioned. Because we can’t know the timing of the BRDC vs. the antibiotic administration, it’s entirely possible the antibiotics were given in response to present or previous BRDC outbreaks. Or, the association they observed could be caused by other unmeasured factors. However, it is possible that feeding antimicrobials to preweaned calves is somehow a true risk factor for higher BRDC.
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