Variation in Milk Protein Concentrations Associated with Genetic Polymorphism and Environmental Factors

Abstract

Concentrations of as-casein, ]3-casein, K-casein, fl-lactoglobulin, a-lactalbumin, serum albumin, and immunoglobulin in milk from 1888 Holstein cows were determined monthly over the lactation period. Cows were phenotyped for genetic variants of asl-casein, ]3-casein, K-casein, and/3-1actoglobulin. Least squares analyses showed variations in individual proteins due to parity number, month of test, stage of lactation, somatic cell count, fat content, milk yield, and phenotypes of cows for milk proteins. ]3-Casein declined and serum proteins increased with advancing age of cows. Concentration of individual proteins decreased during the first 2 to 3 mo in lactation and then increased as lactation progressed. asl-Casein variants significantly affected concentrations of as-casein (BC> BB>AB) and ]3-1actoglobulin (AB>BB>BC). Variant B for ]3-casein is associated with lower as-casein, fl-lactoglobulin, immunoglobulins, and higher ]3-casein and a-lactalbumin concentrations than variant A1, A2, or A3. Milk from BB K-casein, and BB ]3-1actoglobulin cows contained more as-Casein, K-casein, and less ]3-1actoglobulin than milk from AA cows for the two proteins. Concentrations of all proteins were negatively correlated with milk production. Increased somatic cell counts were associated with lower ]3-casein and higher concentrations of other proteins. Fat content of milk was positively correlated with the three casein fractions and ]3-1actoglobulin.