The use of herd management data for development of genetic evaluations to enhance disease resistance in dairy cattle: Preliminary Analysis
Enhancing disease resistance in dairy cattle has economic and welfare benefits and can contribute positively to societal acceptance of agriculture. There are several diseases, including enzootic bovine leukosis (EBL), Johne’s disease (JD), calf respiratory problems, and calf diarrhea, that impact dairy farm profitability for which no genetic evaluations are currently available in Canada. The overall goal of this project is to assess the potential for genetic selection for EBL, JD, and calf respiratory problems and diarrhea, and ultimately incorporate them into a novel resilience index.
EBL and JD are contagious diseases caused by single pathogens, bovine leukemia virus (BLV) and Mycobacterium avium ssp. Paratuberculosis (MAP), respectively, while respiratory problems and diarrhea are caused by various pathogens. Diseases like EBL and JD have a clear impact on cow productivity, health, and longevity. Unfortunately, these diseases are untreatable, and a commercially available vaccine has yet to be developed. Respiratory problems and diarrhea are the main causes of morbidity and mortality in calves. Not only are these calfhood diseases a major welfare concern, but they also impact the profitability of the farm due to costs of treatment and long-term effects on performance.
Animal level data related to EBL (n=84 653 cows), JD (n=223 475 cows), and calf diseases (n=69,385 calves) were provided by Lactanet Canada (Guelph, ON, Canada). For EBL, individual cow milk ELISA test data from 988 herds were analyzed. Eighty-seven percent of herds had at least one test-positive animal for BLV, and an average of 39% of animals in those herds were test-positive. Heritability for EBL was estimated to be 0.09 (SE=0.01). Cows test-positive for MAP were present in 40% of the 2 679 herds in the JD dataset, and those infected herds had an average test-positive prevalence of 3%. Genetic parameter estimation for JD is currently being performed. Respiratory problem records were available for 644 herds, where an average of 15% of calves had at least one recorded case. Records from 425 herds were analyzed for diarrhea, with an average of 12% of calves having at least one case recorded. Heritability estimates for respiratory problems and diarrhea were 0.03 (SE=0.003) and 0.01 (SE=0.001), respectively.
While preliminary, these results provide the groundwork for further development of genetic evaluations for disease resistance in Canadian dairy cattle. Incorporating these traits into the Canadian dairy genetic evaluations may allow for the opportunity to select animals with enhanced disease resistance.
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