Non-genetic factors affecting milk protein profile in Brown Swiss cows

Proteins are one of the most valuable milk constituents since they are entailed on a wide range of nutritional, nutraceutical and technological properties. The aim of this study was to investigate the effects of lactation stage, parity and season on milk protein profile of Italian Brown Swiss cows. Individual milk samples (n = 1,080) were collected in 50 herds. Each cow was sampled once. Quantification of protein fractions (αS1-, αS2-, β-, and κ-casein, α-lactalbumin and β-lactoglobulin) was carried out using reversed-phase HPLC. Sources of variation of protein fractions were investigated through a mixed linear model that included the fixed effects of lactation stage (6 classes of 60 days each, except for the first being a class from 5 to 60 days and the last being a class >300 days), parity (4 classes, with class 4 including cows of parity ≥4) and sampling season (winter, spring, summer, autumn), and the random effect of herd-test day. κ-casein increased significantly along lactation, from 5.78 mg/mL (early lactation) to 6.72 mg/mL (late lactation), in agreement with the trend of other fractions. Protein fractions decreased with parity, being the greatest in primiparous and the lowest in cows of parity ≥4. Except for α-lactalbumin, protein fractions exhibited the same pattern across seasons, with a general decrease in summer.