Stanton PhD Thesis final_docx - Atrium - University of Guelph

feedlots (Van Donkersgoed, 1992). In 1999, 83% of feedlots used oral prophylactic or
metaphylactic antibiotics and 42% of feedlots administered an injectable antibiotic to high-risk
animals to reduce the risk of bovine respiratory disease (USDA, 2000). The experience of beef
cattle entering the feedlot has many similarities with that of dairy calves entering a commercial
heifer raising facility. Both animal types are vulnerable to infection as they are exposed to
disease-causing organisms from multiple sites. Beef cattle are likely to have been recently
weaned, and may have been subjected to a lengthy transportation period which could include
transit through 1 or more sales barns. These stressors are often associated with
immunosuppression (Carroll and Forsberg, 2007). The neonatal dairy calf has a naïve immune
system and relies primarily on colostral antibodies received from the dam. This is a high risk
period for calves; almost one quarter of all calves develop diarrhea in the pre-weaning period,
and 12% of calves experience a respiratory disease event (USDA, 2010). Combining this
susceptibility with mixing of animals from multiple sources may put animals at increased risk of
morbidity and mortality. To date, no study has investigated the effectiveness of a single injection
of a long-acting antibiotic, administered upon arrival at a commercial heifer raising facility, for
the control and prevention of clinical disease.
Tulathromycin (Draxxin, Pfizer Animal Health Group, New York, NY) is a tiamilide
compound, a subclass of macrolide long-acting antimicrobials. It is distinguished by maintaining
therapeutic concentrations against pathogens commonly associated with Bovine Respiratory
Disease complex for up to 10 d (Nowakowski et al., 2004). Tulathromycin is approved for
treatment and control of BRD in beef cattle and nonlactating dairy cattle. Tulathromycin has
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