Association Between Genetic Polymorphism of Milk Proteins and Production Traits During Three Lactations

Abstract

Abstract Polymorphic forms of α s1 casein, β-casein, κ-casein, and β-lactoglobulin were used as genetic markers for milk yield, percentages of fat, and percentages protein during three lactations in 546 Quebec Holstein herds. β-Casein A2A2 cows produced more milk of lower fat content than β-casein A1A1 cows for the first, second, and third lactation. α S1 -Casein types affected milk yield in the second lactation only (BB>AB>BC). Protein content of milk was influenced by phenotypes of κ-casein and β-lactoglobulin for all three lactations. The replacement of A by B allele at the κ-casein locus would increase protein levels in milk by .08, .06, and .04%, respectively, for the first, second, and third lactation. Similarly, replacement of B by A allele at the β-lactoglobulin locus is followed by an increase of .05, .07, and .08% protein for the 3 lactation periods. Because of the relatively low frequency of κcasein B gene (24%) and moderately low frequency of β-lactoglobulin A gene (35%) in the Holstein population, it is possible to increase the protein in milk by proper selection of genetic variants.