Respiratory disease has detrimental effects on the health and welfare of dairy calves and the economic viability of dairy farms, but effective strategies to reduce its incidence and severity by genetic selection are lacking. In this study, a total of 1107 Holstein calves on six Wisconsin dairy farms were assessed at 3 and 6 weeks of age using an established clinical respiratory scoring system and a novel thoracic ultrasonography system to evaluate the incidence and severity of bovine respiratory disease. Incidence rates of pneumonia in thoracic ultrasound exams, including clinical and subclinical lobar and lobular subtypes, were 16% at 3 weeks of age and 20% at 6 weeks of age. The phenotypic correlation between thoracic ultrasound scores at 3 and 6 weeks of age was 0.26. Phenotypic correlations between clinical scores and thoracic ultrasound scores were low, ranging from 0.04 to 0.20, indicating that ultrasonography provides new information about the incidence and severity of pneumonia, especially for calves with subclinical disease. This research provides a new protocol for objective assessment of bovine respiratory disease phenotypes in dairy calves. Pairs of trained evaluators can measure 50 to 100 calves per day on large farms and calf ranches, enabling rapid establishment of large genomic reference populations and facilitating the incorporation of calf health into national genomic evaluation systems. Keywords: dairy, calf, respiratory disease, ultrasonography, genomic selection
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Biology & Species - Bovine (dairy) 1, , 308, 2018
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