Effects of milk protein variants on the protein composition of bovine milk

The effects of ß-lactoglobulin (ß-LG), ß-casein (ß-CN), and -CN variants and ß--CN haplotypes on the relative concentrations of the major milk proteins -lactalbumin (-LA), ß-LG, S1-CN, S2-CN, ß-CN, and -CN and milk production traits were estimated in the milk of 1,912 Dutch Holstein-Friesian cows. We show that in the Dutch Holstein-Friesian population, the allele frequencies have changed in the past 16 years. In addition, genetic variants and casein haplotypes have a major impact on the protein composition of milk and explain a considerable part of the genetic variation in milk protein composition. The ß-LG genotype was associated with the relative concentrations of ß-LG (A » B) and of -LA, S1-CN, S2-CN, ß-CN, and -CN (B > A) but not with any milk production trait. The ß-CN genotype was associated with the relative concentrations of ß-CN and S2-CN (A2 > A1) and of S1-CN and -CN (A1 > A2) and with protein yield (A2 > A1). The -CN genotype was associated with the relative concentrations of -CN (B > E > A), S2-CN (B > A), -LA, and S1-CN (A > B) and with protein percentage (B > A). Comparing the effects of casein haplotypes with the effects of single casein variants can provide better insight into what really underlies the effect of a variant on protein composition. We conclude that selection for both the ß-LG genotype B and the ß--CN haplotype A2B will result in cows that produce milk that is more suitable for cheese production