Milk performance of 717 dairy cows of the Slovakian Pied breed in 1st, 2nd, 3rd and 4th lactations was evaluated from the aspect of alpha(s1)-casein genotypes BE and BC determined by starch gel electrophoresis. The cows came from a herd included in the category of protected herds in Slovakia. alpha(s1)-casein genotype BE was determined in 687 animals (95.8 %), genotype BC in 30 animals (4.2%). The basic description of performance indicators (milk, fat, protein, lactose) shows a clear trend of their quantitative increase in the group of cows with heterozygotic alpha(s1)-casein genotype combination BC of (Tabs. I to IV). The results confirmed statistically significant differences (P < 0.05) between milk production (BC > BE) in the first lactation (by 473 kg) and average fat production (BC > BE) also in the first lactation (by 20 kg). At summary evaluation of commercial characteristics of cows for all four standardized lactations significant differences (P < 0.05) were calculated, in view of alpha(s1)-casein polymorphism, in average milk production (BC > BE) (by 515 kg) and average lactose production (BC > BE) (by 23 kg).
