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

Department of Animal Science, Macdonald College of McGill University, 21,111 Lakeshore Road, Ste. Anne de Bellevue, Quebec, Canada H9X 1C0

ABSTRACT

Concentrations of _s-casein, ß-casein, -casein, ß-lactoglobulin, -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 _s1-casein, ß-casein, -casein, and ß-lactoglobulin. 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. ß-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. _s1-Casein variants significantly affected concentrations of _s-casein (BC>BB>AB) and ß-lactoglobulin (AB>BB>BC). Variant B for ß-casein is associated with lower _s-casein, ß-lactoglobulin, immunoglobulins, and higher ß-casein and -lactalbumin concentrations than variant A1, A2, or A3. Milk from BB -casein, and BB ß-lactoglobulin cows contained more _s-casein, -casein, and less -lactoglobulin 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 ß-casein and higher concentrations of other proteins. Fat content of milk was positively correlated with the three casein fractions and ß-lactoglobulin.