Genetic associations of colostrum yield with antibody concentrations and gross composition for selective breeding in Italian Holsteins

The quality of bovine colostrum (BC), primarily determined by the concentration of IgG, is essential for the transfer of passive immunity and the development of the gastrointestinal tract in neonates. High IgG concentration in BC is pivotal for the calf at the first meal, but neonates often refuse to voluntarily drink the recommended amount in the first hours of life, and dams frequently fail to produce a sufficient volume of colostrum at first milking. This study seeks to estimate the h² of colostrum yield (CY) and its genetic correlations with total Ig and IgG, protein, and fat concentrations for the first time in the Italian Holstein population. Colostral Ig concentration and gross composition were assessed on individual samples collected using ad hoc near-infrared spectroscopy prediction models. The infrared-predicted traits, along with the measured CY, were used as phenotypes (n = 2,938) for the estimation of genetic parameters through linear animal models. Parity, photoperiod at calving, and classes of CY significantly altered colostral composition, with parity having the most important influence. Colostrum of older cows, in fact, had greater total Ig, IgG, and protein concentrations than colostrum of younger cows. Colostral quality and CY were higher when calvings occurred in months with decreasing photoperiod. Also, CY was maximum in second-parity cows. Heritability estimates of IgG and total Ig concentrations were 0.225 ± 0.05 and 0.211 ± 0.05, approximately twice the h² estimate for CY (0.101 ± 0.03). The correlation between CY and IgG concentration was positive (0.219 ± 0.032) at the phenotypic level and negative at the genetic level (−0.147 ± 0.190). Spearman rank correlations between EBV of the colostrum traits and official EBV and indexes, for which selection is ongoing in the Italian Holstein breed, were generally weak or moderate and not always significant. Specifically, CY was unfavorably associated with the PFT (production, functionality, and type; −0.300) and the IES (economic health; −0.335) indexes, and IgG concentration was favorably linked to the official indexes for udder health/mastitis resistance (0.154) and fertility (0.166), mirroring those calculated for total Ig. Selection toward an intermediate optimum for CY at calving can be potentially pursued in the Italian Holstein breed through a balanced index without incurring additional costs for IgG concentration.