Hematological variables as predictors of bovine respiratory disease in newly received cattle fed in confinement
Fontenot, Lauren Rose
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Bovine respiratory disease (BRD) is the most common and costly health disorder in the US cattle feeding industry. Although antimicrobial metaphylaxis has been proven to be effective in reducing BRD morbidity rate and improving performance, today’s beef consumers are demanding a reduction or cessation of antimicrobial use in food animals. This study sought to elucidate if hematologic variables determined upon feedlot arrival were associated with risk for BRD. If accurate and timely classification of health risk is possible, antimicrobial metaphylaxis could be refined for those animals identified at risk for BRD development. Utilizing hematologic information of 502 steers and bulls with unknown previous health history, we categorized individuals for each complete blood count (CBC) variable in two ways: 2-level categorization determined by receiver operating characteristic (ROC), and 3-level categorization determined by simple quartile division. A reduced eosinophil status upon arrival, expressed as a percentage of total leukocytes or as concentration, was correlated with increased odds (OR>1.6; P<0.04; CI = 1.03 to 2.57) of BRD morbidity outcome for 2- and 3-level categorizations. Animals with reduced hemoglobin and/or increased red blood cells (RBC) were determined to be at lesser risk (OR<0.7; P<0.04; CI 0.42 to 0.98) to be treated once for BRD based on 2-level categorization. Those in the lowest quartile for relative neutrophils and neutrophil:lymphocyte ratio (NLR) had increased risk (OR>1.9; P=0.02; CI = 1.05 to 3.70) of being treated once for BRD in the 3-level categorization. Likewise, decreased percentage of lymphocytes in peripheral blood was associated with decreased mortality risk (OR<0.2; P<0.04; CI = 0.13-0.95) in both categorization methods. In concert with low percentage lymphocytes, a low NLR was also associated with increased mortality risk (OR>5; P=0.03; CI = 1.47 to 24.03) in the 3-level model, and reduced neutrophil concentration was associated with increased mortality risk (OR>2; P=0.02; CI = 1.14 to 6.29) in the 2-level model. Because eosinopenia has been previously reported in multiple mammalian species to be predictive of poor health outcomes, this particular variable may hold promise for use in feedlot health management decisions upon arrival.