Genetic associations of colostrum yield with antibodies concentration and gross composition for selective breeding in Italian Holsteins.

The quality of bovine colostrum, primarily determined by IgG concentration, is essential for the transfer of passive immunity and the development of the gastrointestinal tract in neonates. High IgG concentration in bovine colostrum (BC) is pivotal for the calf at first meal; however, while neonates often refuse to voluntarily drink the recommended amount of BC in the first hours of life, the dam frequently fails to produce a sufficient volume of colostrum at first milking. This study seeks to estimate the h of colostrum yield (CY) and its genetic correlations with total Ig, 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 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 of the dam significantly impacted on the colostral composition, with parity having the most substantial 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 h 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/indexes for which there is selection ongoing in Italian Holstein breed were generally weak or moderate, and not always significant. Specifically, the CY was unfavorably associated with the PFT (production, functionality, and type; -0.300) and the IES index (economic health; -0.335), and IgG concentration was favorably linked to the official index 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 the IgG concentration.