Breeding and Genetics: Genetics of Dairy Health Traits

Genetic selection programs for dairy cattle in many countries are reviewed, breeding goals are compared, and the degree of uniformity that exists and is required for international genetic programs for health traits is discussed. The most prevalent health disorders in dairy cattle are mastitis, infertility, lameness, milk fever, ketosis, metritis, and displaced abomasums. The manifestation of these disorders can be partly attributed to management and environmental factors, but there is evidence that each also has a genetic component. Health traits are genetically correlated with traits for which international genetic evaluations are routinely available from Interbull, including milk production, conformation, and udder health traits. Evaluations for longevity (length of herd life) are expected this summer. Genetic evaluations for female fertility traits are available in many countries and international evaluations are imminent. Effective selection using quantitative genetic approaches requires measurement and recording of phenotypes and frequent evaluation of candidates for selection. Producers use many different definitions to record health data and do not use a standardized format in on-farm or DHIA databases. Change will require significant time and effort by many people. Direct genotyping using DNA technologies offers potential for direct selection for genes causing health problems, but this is likely to be a slow and incomplete solution. Potential exists for genetic improvement of health in dairy cattle. Economic, social, and political forces will shape the changes that occur.