Date of Award
Master of Science
Troy N. Rowan
Troy N. Rowan, Lew G. Strickland, Marc JM. Caldwell
Bovine respiratory disease is a multifaceted disease with agent, host, and environmental factors. Stocker calves are at high risk of contracting the disease through many stressors like weaning, transportation, commingling, etc. The purpose of this project was to test if externally observed physical characteristics of calves on arrival at a stocker facility can be used to predict calfhood vaccination status determined based on antibody titer levels. Knowledge of highly correlated characteristics could allow stocker operators to reduce the occurrence of BRD through targeted management strategies, thus lowering morbidity, mortality, and treatment costs. Ear notches, blood, and visual characteristics were collected for 408 stocker calves at four farms in Tennessee. Each animal was tested for Bovine Viral Diarrhea Virus-Persistently Infected status and titer levels for three known viral agents. Multiple visual characteristics were predictive of immunization status, including the presence of a prior ear tag (1.6 times), heifers (0.82 times), steers (1.26 times), polled cattle (4.8 times), body condition score increasing by one (1.46 times), and possessing health records (2.2 times). When analyzed together, the calf factors of sex, tag, and possessing health records remained the most universally informative. When we evaluated the predictive nature of multi-variable models, predictability was generally low. Despite low model accuracy, this initial work creates a good foundation for further research focused on more robust data collection to build more robust models.
Additionally, we followed sixty calves through the stocker phase to ascertain the downstream impacts on health and production of preconditioning. We found that preconditioned calves had lower BRD incidence, had a higher presence of detectible titers, and gained more weight over 60 days than naïve cattle. However, many calves marketed as preconditioned did not have detectible viral titers on arrival. This work identifies practical solutions for stocker operations to make more informed purchasing and management decisions. It also lays the groundwork for future work identifying ways to deliver precision management to stocker cattle.
Hunkler, Claire E., "Predicting Immunization Status at Arrival in Tennessee Stocker Calves. " Master's Thesis, University of Tennessee, 2022.