Genome-wide association study reveals key genomic regions underlying colostrability in Italian Holstein cattle

Colostrum yield (CY, L) and concentration of immunoglobulin G (IgG, g/L) are important phenotypes to monitor in dairy farms because of their association with the risk of failure of the passive transfer of immunity in the newborn calf. This can occur when the CY of the parturient cow is insufficient or when the IgG concentration is low. Given that both of these traits are heritable, the present study aimed to investigate their genetic determinism by identifying significant genomic regions. A genome-wide association study coupled with an exploratory functional enrichment analysis was carried out to provide preliminary biological context of the detected signals for the 'colostrability' defined as the cow's ability to secrete enough volume (≥ 4 L) of good-quality colostrum (≥ 50 g IgG/L) at calving. Data comprised 960 genotyped Italian Holstein cows with CY recorded within 6 h of calving, together with colostral IgG and total immunoglobulin concentrations.

The significant SNPs associated with CY were scattered across BTA3, 5, 10, 11, 21, and 22, with 23 genes on BTA22 either harbouring or flanking significant signals. Apart from some genes already known, part of the significant regions have unclear function. Signals were detected on BTA1, 6, 7, 11, 19, 21, and 25 for IgG concentration, and on BTA6, 7, 11, 21, 23, and 25 for total immunoglobulin concentration. The functional enrichment analysis provided preliminary support for possible involvement of secretory, immune-signalling, and epithelial receptor-related processes.

This study confirms the polygenic nature of cows' 'colostrability' being regulated by different genomic regions distributed across the genome. However, exploration of the genomic determinism of CY and immunoglobulin concentration requires larger, independent, and harmonized data, ideally standardized and highly comparable. These findings, although relevant for improving calf health, represent only part of a more complex picture when the goal is selective breeding toward calf health. In addition to dam-related data, including colostrum traits, future studies should integrate calf-related phenotypes associated with failure of passive transfer of immunity, such as intestinal IgG absorption capacity, gut permeability, early-life survival, and health outcomes.