Impact of inbreeding on milk fatty acids of a Brazilian Holstein cattle

Context. Reproductive technologies may either contribute to the increase of genetic gains or inbreeding levels in dairy cattle breeding programs and herds. In general, studies have evaluated the impacts of inbreeding on traditional traits, such as production and reproduction. However, studies on novel traits, such as milk fatty acids profile, are scarce in the literature. Aim. We aimed to evaluate the impact of inbreeding levels on milk fatty acids profile measured in a Brazilian Holstein cattle population. Methods. Monthly records of the percentages (%) of palmitic, stearic, oleic, total saturated, unsaturated, monounsaturated and polyunsaturated fatty acids in milk were collected from 2047 Holstein cows between May and December 2012. The pedigree file contained 7963 animals over seven generations. The inbreeding trend was evaluated by linear regression of inbreeding coefficients on generations. The inbreeding impacts on breeding and phenotypic values were evaluated by linear regression of breeding values and phenotypic values on generations respectively. Breeding values were obtained by a Bayesian approach based on an animal model that included the systematic effect of contemporary group, cubic effect of days in milk as a covariate, and the random direct additive genetic and animal permanent environmental effects. Key results. The average inbreeding coefficient was 0.28% for all animals, and 1.39% for inbred animals. Inbreeding tended to increase 0.24% per generation (P-value <0.0001). The regression coefficients of phenotypic values on inbreeding were not significant for saturated, unsaturated, monounsaturated, palmitic, stearic and oleic fatty acids (P-values >0.18, 0.10, 0.16, 0.26, 0.51 and 0.09 respectively); whereas for polyunsaturated fatty acids, they were significant (P-value <0.04), with an increase of -0.000978% on phenotypic values for each 1% increase in inbreeding. The regression coefficients of breeding values on inbreeding were not significant for unsaturated, monounsaturated, polyunsaturated, stearic and oleic fatty acids (P-values >0.33, 0.78, 0.48, 0.32 and 0.07 respectively). However, they were significant for saturated and palmitic fatty acids (P-values <0.03 and 0.0001 respectively), presenting an increase of 0.000689% and 0.000283% respectively on breeding values for each 1% increase in inbreeding. Conclusions. There was a significant increase in inbreeding coefficients over the studied generations; however, the impacts on both breeding and phenotypic values were small, when significant.