Relationships Between Milk Protein Polymorphisms and Major Milk Constituents in Holstein-Friesian Cows

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Abstract
Milk samples from 1,908 Holstein Friesian cows were phenotyped for genetic variants of .alpha.s1-casein, .beta.-casein, .kappa.-casein, and .beta.-lactoglobulin. The relationships between milk protein polymorphism and test day milk yield and composition were investigated. After adjustments were made for environmental effects of herd, parity number, month of test, stage of lactation, age of sample at testing, and somatic cell count, milk protein phenotypes were found to be associated with milk yield; concentrations in fat, protein, casein, and whey protein; and proportion of casein in protein. Higher test-day milk production was associated with .alpha.s1-casein BB, .beta.-casein A1A3, .kappa.-casein AA, and .beta.-lactoglobulin AA phenotypes. Fat and protein concentrations were highest in milk from cows of .alpha.s1-casein BC, .beta.-casein A1B, and .kappa.-casein BB phenotypes. .beta.-Lactoglobulin BB milk was associated with higher percentages of fat and casein and with lower percentages total protein and whey protein. Based on desirable fat and casein contents of milk for cheese production, it would be advantageous to select for cows bearing .kappa.-casein BB and .beta.-lactoglobulin BB phenotypes.