Genotype effects of milk and blood protein polymorphisms on milk performance traits in East Friesian and black and brown milk sheep

The frequency of milk protein variants alpha(S1)-casein, alpha(S2)-casein, beta-casein, kappa-casein, alpha-lactalbumin and beta-lactoglobulin as well as the effects of the polymorphic milk proteins alpha(S2)-casein, beta-casein and beta-lactoglobulin on milk performance traits of 72 milk sheep from Lower Saxony were investigated. For the analysis of the blood protein polymorphisms of hemoglobin, carboanhydrase, transferrin, albumin and vitamin-D-binding protein 122 milk samples of milk sheep were available. The genotype effects of protein variants on milk performance traits were estimated by using a test day model with fixed regression. The model included the fixed effects of breed, region, lambing season, lambing year, lactation number and number of lambs born. The herd and animal effect were treated as random and the days in milk as linear and non-linear covariates. The milk protein variants of beta-casein showed a significant relationship to protein content and the milk protein variants Of alpha(S2)-casein to milk yield. For the milk protein variants of beta-lactoglobulin milk performance traits were not significantly correlated. The association analysis for the blood protein variants of transferrin revealed a significant effect on milk and protein yield and for hemoglobin a significant association to protein content. The variants of the vitamin-D-binding protein showed no effect on the analysed milk performance traits.