Milk data (n = 59,811) from 4,355 Holstein cows were used to estimate genetic parameters for lactose percentage (LP) and yield (LY), and other milk traits. Analysis of variance revealed a similar trend during the lactation between LP and milk yield. Heritability and repeatability of the investigated traits were assessed through univariate animal models, and genetic correlations with milk somatic cell score (SCS) and freezing point (FRP) were estimated using bivariate analyses. Fixed effects were herd-test-date, lactation stage, parity, calving season and the interaction between parity and stage of lactation. Animal, permanent environmental cow and residual were the random effects. Lactose percentage showed the highest estimates of heritability (0.44) and repeatability (0.59), whereas SCS and FRP showed the lowest estimates of heritability (0.12 and 0.11, respectively) and repeatability (0.26 for both traits). Lactose percentage was moderately correlated with SCS both phenotypically (-0.34) and genetically (-0.25), suggesting that there are opportunities for considering LP as a potential trait to indirectly select for resistance to mastitis along with SCS. Freezing point was negatively genetically correlated with LP (-0.46), evidencing that there is an inverse genetic relationship between these two traits. Further studies are required to evaluate correlated responses for all traits, allowing LP, LY and FRP to be considered as a part of the current selection index or breeding objective of Italian Holstein dairy cattle. Keywords: lactose, somatic cell score, freezing point, milk, genetic parameter

Angela Costa, Massimo De Marchi, Martino Cassandro, Giulio Visentin, Nicolas Lopez-Villalobos, Mauro Penasa

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume Electronic Poster Session - Biology & Species - Bovine (dairy) 2, , 478, 2018
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