Sheep milk protein polymorphism and its effect on milk performance of Polish Merino

A total of 207 Polish Merino sheep from central Poland were investigated. Ewes lambed in late autumn and reared their lambs until 49 days of age. After weaning the lambs, ewes were milked mechanically twice daily for up to 14 weeks. Milk yields were recorded once in two weeks. The following milk proteins were genotyped with polyacrylamide gel electrophoresis under acidic conditions and using isoelectric focusing: α-La, αS1-CN, β-CN, β-Lg. Taking into account the results of 770 lactations, the effects of genotype of the analysed milk proteins on milking duration, milk yield and basic composition were evaluated. The sheep population studied was monomorphic for α-La and polymorphic for αS1-CN, β-CN, β-Lg. The greatest genetic variation (4 genotypes and 4 genes) occurred within αS1-CN. Within β-Lg locus there were two alleles of almost identical frequency. Sheep with the CC αS1-CN genotype exhibited a statistically significant advantage in terms of fat and solids percentage over sheep with the AC αS1-CN genotype, and those with the AA β-CN genotype were highly significantly better in terms of protein and solids percentage than sheep with the AB β-CN genotype. BB β-Lg genotype sheep were characterized by a significantly higher protein content of milk than sheep with the other two β-Lg genotypes - AA and AB.