VARIABILITY OF THE MILK PRODUCTIVITY OF KHOLMOGORY AND BLACK MOTTLE COWS WITH DIFFERENT PROLACTIN GENOTYPE
The variability of the characteristics of milk productivity of cows for the 1st and 3rd lactation in black-and-white (151 and 168 heads and the Tatarstan type of the Kholmogory breed (160 and 143 heads) with different genotypes of the prolactin gene was studied. When comparing breeds in terms of variability of milk productivity, high variability is typical for first-calf heifers of Kholmogory cattle. The highest indicators of the coefficient of variability of milk productivity traits were found in cows with the PRL AA and PRL AB genotypes, while in homozygous black-and-white cattle, reliability was detected in terms of milk yield by 3.95% (P<0.01) and milk protein yield by 3, 46% (P<0.05). According to all signs of milk productivity in Kholmogory cows, the advantage of variability is inherent in animals carrying the allele A of the prolactin gene in their genotype, with a significant advantage over first-calf heifers with the PRL AA genotype in terms of the mass fraction of fat in milk by 3.21% (P<0.001), according to the amount of milk fat - by 8.6% (P<0.01) and milk protein - by 8.23% (P<0.01), and for the 3rd lactation of animals over animals with the PRL AB genotype in terms of milk yield by 3 87% (P<0.05), mass fraction of fat in milk - by 1.98% (P<0.01), milk fat - by 2.69% (P<0.05), milk protein - by 4.47% (P<0.05). Consequently, in herds dominated by individuals that have allele A of the prolactin gene in their genotype, the most effective selection for the level of milk production will take place.