ESTIMATES OF DIRECT AND MATERNAL GENETIC EFFECTS FOR MILK TRAITS IN FRIESIAN COWS

Direct and maternal genetic effects on milk traits in dairy cows are very important elements for estimating the best genetic parameters. The present work aimed to estimate phenotypic and genetic parameters for productive and reproductive traits. Variance components and genetic elements were estimated, using records of 2166 lactations of Friesian cows’ progeny of 92 sires and 882 dams from 2014 to 2020. Two animal models were constructed, and whether or not maternal genetic effects were considered. The variables studied are ten-month milk production (10 MMP), ten-month fat production (10 MFP), ten-month protein yield (10 MPP), lactation length (LL), days dry (DD), age at first parturition (AFP), days open (DO) and calving interval (CI). Phenotypic and genetic correlations among all variables studied were calculated. Estimated direct heritability (h2d) ranged from 0.23 to 0.25 for 10 MMP, from 0.20 to 0.27 for 10 MFP, from 0.19 to 0.26 for 10 MPP, from 0.03 to 0.06 for LL, from 0.03 to 0.06 for DD, from 0.01 to 0.04 for AFP, from 0.06 to 0.10 for DO and from 0.04 to 0.05 for CI. The estimates of maternal heritability (h2m) were 0.23, 0.20, 0.19, 0.03, 0.03, 0.04, 0.06 and 0.05 for the above variables studied, respectively. Therefore, maternal genetic effects should be considered in the animal model for genetic evaluation of milk production and its components. Therefore, the current study recommends improvement of milk production efficiency and milk component variables through selective breeding strategies targeting both bulls and cows. While direct h2 estimates showed that the greatest difference in fertility variables is influenced by environmental elements, which can be improved by using a better feeding system and controlling heat stress.