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The Effect of Respiratory Disease on Lying Behavior in Holstein Dairy Calves
The objective of this cohort study was to determine the effect of naturally occurring bovine respiratory disease (BRD) on lying behavior in preweaned Holstein dairy calves. This study was carried out on one commercial dairy in south western Ontario, Canada during November and December 2012. Calves were enrolled at 10 days of age and were grouped according to vaccination status (n = 19 vaccinated and n = 20 unvaccinated). Each calf was examined at weekly intervals for signs of BRD before and during the peak 4 week period when calves are at risk for developing disease. Respiratory scoring (RS) and thoracic ultrasonography (US) were performed at each of the five visits. Individual electronic accelerometers recorded lying behavior throughout the 4 week period. Descriptive statistics and repeated measures linear models were developed using commercially available software. Fever, sickness, and lung consolidation increased from 11%, 3%, and 0%, respectively, at the first examination to 33%, 33%, and 58%, respectively, at the last examination (P < 0.05). Overall, calves spent 20.6 ± 0.7 h/d (mean ± SE) or 86% of the day lying down when all variables were set to the referent. Lying time (LT) decreased by 4 ± 1 min/d for each successive day of age. Fever was associated with 44 ± 14 min/d additional LT. Calves housed in group pens had lower but not statistically significant LT than those housed in single pens. Also, housing type confounded the LT estimate for age. Ultrasonographic lung consolidation and health status (RS > 4) were not significantly associated with LT. Lying bout duration (BD) was 72 (61 – 85) min/d (median; IQR), and the lying bout frequency (BF) was 16 bouts per day (13 – 18) (median; IQR). Health status and lung consolidation were not significantly associated with BD or BF. Fever numerically increased BD but was not associated with BF. Monitoring LT in preweaned dairy calves might have a place in identifying febrile animals requiring individual examination and possible intervention. Further studies are needed to determine if early identification and treatment of animals experiencing fever improves future health and performance as compared to traditional methods of disease detection. Lastly, researchers should consider monitoring rectal temperature during behavioral studies to assess for bias due to undetected fevers.
Keywords: dairy calf pneumonia, accelerometer, ultrasonography