Milk protein polymorphisms in Holstein cattle

Milk samples from 203 Holstein cows were phenotyped for genetic variants alpha(s1)-casein, beta-casein, kappa-casein and beta-lactoglobulin using starch-gel electrophoresis. All of the four milk protein loci exhibited polymorphism with allele frequencies of 0.862 +/- 0.017 for alpha(s1)-casein B, 0.966 +/- 0.0009 for beta-casein A, 0.712 +/- 0.0224 for kappa-casein A and 0.567 +/- 0.0245 for beta-lactoglobulin B. The mean heterozygosity estimated over all the four milk protein loci was 0.3015. Genetic equilibrium was observed among all of the loci investigated, except kappa-casein. Chi-squared tests revealed that there was no significant linkage among studied milk protein phenotypes.