Relative quantitative proteomic profiling of bovine colostrum and transition milk at onset of lactation.

Colostrum, the first postpartum secretion of the mammary gland, plays a vital role in the nutrition, development, and immunity of a newborn calf. We characterised the protein profile as milk transitions from colostrum to transition milk over the first 5 days of lactation, collecting samples on d0, d2 and d5 after calving. Protein concentration decreased significantly after d0 (colostrum) before stabilising. Principal component analysis revealed samples clustered by day postpartum, with a limited effect from parity. In total, 471 proteins were identified across all samples; 199 protein groups showed altered relative abundance by day of lactation (fold change ≥2, P < 0.05), but none were altered significantly by parity. Higher relative levels of immune proteins were found in colostrum, and milk fat globule membrane proteins were found to increase over early lactation. Our findings provide a better understanding of the dynamics of the protein profile of bovine milk in early lactation. [ABSTRACT FROM AUTHOR]