Genomic Selection for Enhanced Immune Response to Improve Dairy Cattle Health

Diseases that affect dairy cattle contribute to substantial economic loss. The inclusion of immune response (IR) traits in breeding objectives shows promise for improving inherent animal health. Previously, dairy cows classified as High Immune Responders in herds across Canada and one large herd in the US were found to have improved response to vaccination, increased milk and colostrum quality and a decreased occurrence of diseases including mastitis, metritis, ketosis, retained placenta and Johne’s. The objective of this research was to perform a genome-wide association study to determine genetic profiles associated with antibody-mediated IR (AMIR). A total of 680 Holstein cows from 58 herds across Canada were immunized with a type 2 test antigen to measure serum antibody. High (n=81) and Low (n=82) AMIR cows were genotyped using the Illumina Bovine SNP50. A generalized quasi-likelihood score method was used to determine SNPs associated with AMIR. A total of 198 SNP were significantly associated with AMIR, based on a chromosomal false discovery rate of 0.05. Of these, the majority (83%) were on chromosome 23, which contains the bovine Major Histocompatability Complex (MHC). Candidate genes within 250,000 base pairs of the significant SNPs included genes in the MHC, complement system and cytokines, including interleukin-17. Based on these genes, various biological pathways associated with AMIR were identified, including the antigen processing and presentation pathway, important in host defense. The significant genetic variation associated with AMIR in this study suggests that including AMIR in genomic selection could help decrease the incidence of disease in the dairy industry.