Effect of Kappa-Casein and Beta-Lactoglobulin Loci on Milk Production Traits and Reproductive Performance of Holstein Cows

The effects of κ-casein (κ-CN) and β-lactoglobulin (β-LG) loci on milk production traits (milk, fat, protein, and lactose yield, fat, protein, and lactose content) and reproductive performance (gestation length, calving interval, age at first and second calving, number of services per conception) was estimated for 278 Holstein cows in the first 2 lactations. Genotypes of κ-CN and β-LG were determined by alkaline and acidic polyacrylamide gel electrophoresis. Milk production was recorded daily. Single-trait, mixed, linear models were used for the statistical analysis of the data. Results indicated that κ-CN genotypes affected significantly protein yield and content (genotype AB > genotype AA). A tendency for increased milk and fat yield of animals having AB κ-CN genotype was also found. Fat content and lactose yield and content were not affected. In the β-LG system, significant differences were detected for milk yield (AB > AA), fat yield (BB and AB > AA), fat content (BB > AA and AB), and lactose yield (AB > AA). A tendency for higher protein yield was also observed (AB > AA). The β-LG locus had no significant effect on protein and lactose content. No associations between polymorphisms at the κ-CN locus and reproductive performance were found. There was a tendency, however, for cows with AB genotype to have older age at first and second calving. In the β-LG system, cows with AA genotype had significantly shorter gestation length than did those with AB or BB genotype. No differences were detected between β-LG polymorphisms for the other reproductive traits.