Estimation of dominance effects related to mastitis and production traits for CXCR1 gene using logistic regression analysis in dairy cattle

The dominance effect is important for mastitis, which is the major source of economic loss in dairy herds. The objective of this study was to evaluate dominance effects of CXCR1 gene for clinical mastitis and production traits in Holstein dairy cattle using the selective genotyping method. Records of 305-day lactation were obtained for production traits and for the number of cases of clinical mastitis per lactation. Cows were selected based on extreme values (highest and lowest CMR values) for clinical mastitis residuals (CMR) from mixed model analyses. Each of the two extreme groups of cowswas genotyped for CXCR1 gene and then, associations between genotypes and CMR and also breeding values for traits of interest were estimated by applying logistic regression analyses. Allele G of CXCR1 gene was associated with fewer cases for clinical mastitis (CM), and showed desired effects on production traits, especially on milk, protein and fat yield. Effects of dominance ranged from − 0.03 SD to 0.55 SD for the production traits and CM. For milk production traits, positive values for dominance indicated a surplus in these traits. Result showed that CXCR1 gene may be a valuable candidate gene for improvement of mastitis resistance as well as production traits in dairy cattle herds and the dominance effects may not be negligible.