Protein profiling of bovine colostrum and transition milk

The protein profile of bovine milk serum was characterised as milk transitions from colostrum to transition milk over the first 5 days of lactation. Samples were collected from first and third parity cows at days 0, 2, 5 (D0, D2, D5) after calving. Following isolation of the milk serum fraction, label-free quantitative proteomics was carried out following normalisation by total protein concentration. Protein profiles indicated samples clustered by day postpartum, but not by parity. Proteins (n = 471) were identified and relative quantification was performed, with 199 protein groups showing altered abundance by day of lactation (fold change ≥ 2, P < 0.05). Elevated levels of immune proteins, including immunoglobulins and complement proteins were detected in colostrum with levels significantly decreasing by D2. These findings provide an outline of the dynamics of the protein profile of bovine milk and colostrum in early lactation.