Genetic markers associated with high and low immune response phenotypes and its implication for disease

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Recording of on-farm disease occurence of dairy cattle is subject to many environmental factors, including data recording practises, herd management and pathogen exposure. As a result the heritability of disease traits are quite low, generally below 0.10. Immune response (IR) traits, on the other hand, are critical to control disease and are better defined for each animal with a much higher heritability (~0.25). Therefore, while disease recording is a prerequisite for the validation of any selection strategy to improve health, selection for IR should be a more powerful way to increase resistance to a broad range of pathogens versus direct selection on disease traits. In fact, the immune system is designed to control disease and individuals that can make a robust immune response are expected to have health advantages. At the University of Guelph, researchers have developed a patented test system to identify animals with enhanced or High Immune Response (HIR). HIR dairy cattle have been shown to be at lower risk of disease (e.g. mastitis, metritis, ketosis), respond better to commercial vaccines (e.g. J5 E. coli) and have improved colostrum quality compared to low or average immune responders. HIR animals are expected to require less therapeutic intervention, including antibiotics, thereby improving milk and meat quality. Our group has recently also demonstrated that it is possible to identify high, average and low immune responder dairy sires. This means that producers could select HIR sires to help improve overall herd health. Ongoing research is focused on learning more about the genetic and epigenetic mechanisms that influence these unique and important phenotypes. One of the next critical steps to improve understanding of the HIR technology is to perform genome-wide association studies to search for genetic markers associated with immune responsiveness. The results of the proposed study are expected to provide novel insight into the potential inclusion of immune response traits in genetic selection with the goal of improving inherent health and decrease the occurrence of disease in Canadian dairy cattle.