Genetic and phenotypic trends for milk fatty acids in a Holstein cattle population reared under tropical conditions

Evaluation of genetic and phenotypic trends is important to monitor the evolution of dairy cattle breeding programs. Traits that are not commonly included as selection goals should also be monitored, especially when they have some effect on consumer health, such as milk fatty acids profile. Thus, the aim was to evaluate the genetic and phenotypic trends of the milk fatty acids composition on a Holstein dairy cattle population, from three farms, reared in a tropical environment. Monthly records of palmitic (C16:0), stearic (C18:0), oleic (C18:1), total saturated (SFA), unsaturated (UFA), monounsaturated (MUFA), and polyunsaturated (PUFA) fatty acids content in milk (g/100 g of milk), were collected of 2047 Holstein cows from three Brazilian farms between May and December of 2012. The pedigree file contained 7963 animals of seven generations. Genetic and phenotypic trends were obtained by linear regression of breeding values or phenotypic values, respectively, over generations. Single-trait analyses were performed and the breeding values were estimated using Bayesian approach. All traits showed negative phenotype trend (- 0.02723 g/100 g of milk to - 0.00395 g/100 g of milk), indicating reduction of the phenotypic value over generations. According to the genetic trends for MUFA and PUFA (- 0.00023 and - 0.00005, respectively, in g/100 g of milk) the breeding values of the animals were reduced throughout the generations, while for SFA, C16:0 and C18:0 the genetic trends (0.00134, 0.00052 and 0.00013, respectively, in g/100 g of milk) showed an increase in breeding values, possibly due to correlated effects originated from selection protocols applied to the herd. The linear regression coefficients of the genetic values in the generations were not significant for UFA and C18:1 (p-value > 0.6226 and p-value > 0.9708, respectively). Significant genetic and phenotypic trends of small magnitude were obtained, which may be a consequence of the absence of direct selection for these traits in these populations. Genetic and phenotypic gains for fatty acids profile in milk should be monitored to guide breeding programs in their selection objectives. It is suggested to investigate the causes of possible correlated response in the studied populations. (AU)