MILK PROTEIN POLYMORPHISMS IN CALIFORNIA DAIRY-CATTLE

Milk samples from 1454 first lactation heifers were collected from five breeds of cattle in a representative sampling of the California dairy cattle population. Samples were phenotyped for alpha-s1-casein, beta-casein, kappa-casein, and beta-lactoglobulin using PAGE. Lactation yields for milk, fat, and protein were available on 1166 heifers. Genetic linkage of the casein loci and the relationship between milk protein genotypes and production parameters (milk, fat and protein yield, fat and protein percentage) was investigated. Gene frequencies were similar to those found in other studies of the American dairy cattle population. Linkage was found between beta-casein and kappa-casein in four of the five breeds and between beta-casein and alpha-s1-casein in the Jersey breed. Casein haplotypes BBB and CA3A (alpha-s1-, beta-, kappa-casein respectively) occurred in the Holstein population more often than would be expected from a random combination of the alleles. Least squares analysis of the production data indicated that the only significant effect was that of kappa-casein genotype on protein yield; the highest yields were obtained for the BB genotype.