"Metaphylaxis is commonly used to treat bovine respiratory disease (BRD) in the United States (US) feedlot industry. It is costly to the spread of antibiotic resistance and is expensive for producers to implement (Dean, et. al, 2011). Neutrophils and lymphocytes, two types of white blood cells (WBC), are key components early in the immune response to bacterial infection, and their numbers fluctuate in response to stress and bacterial pathogens (Parkin and Cohen, 2001). We hypothesize that selective treatment based on abnormal white blood cell (WBC) counts would result in significantly reduced morbidity rates compared to cattle that did not receive antibiotics. Selective treatment based on WBC count would also lessen overall antibiotic usage compared to metaphylaxis, without significant increases in morbidity or mortality rates. Two studies were conducted where cattle were randomly assigned to treatments. The control treatment (CON) was not treated with antibiotics, the second treatment was treated metaphylactically (MET), and the third treatment was selectively treated based on WBC count (SEL). In the first study, no significant treatment differences were observed. The study was considered inconclusive due to low BRD incidence. In the second study, cattle with a rectal temperature >39.4°C at processing were given antibiotics (FEV). No treatment differences were observed, supporting the theory that selective antibiotic treatment may reduce antibiotic usage. Seasonal differences were significant, with highest morbidity observed in the fall."--Page ii.
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