Performance and reproductive capacity of high performing cows depending on the hereditary factors
Lactation performance of first-calf cows black and white breed was studied in a breeding farm in Tver region for a number of years. The lactation performance was increased in milk yield, mass fraction of protein and the total yield of fat and protein. In 2015 the milk yield of first-calf cows was 7703 kg, for the period under study it was increased by 608 kg, the total yield of fat and protein was increased by 59 kg. The most performant were firstcalf cows of Reflection Sovering line, their milk yield for305 days of lactation was higher than that of cows of Montwick Chieftain line by 563 kg (7.4%), than that of Vis Back Ideal line by 165 kg (2.2%), than that of Ceiling Tryjune Rocket line by 103 kg (1.4%). The herd consisted of a domestic breeding stock, the nuclear stock of which was formed by the selection of the best individuals and with the use of semen of valuable improving bulls. Daughters of Equipage 1819 bull had the highest milk yield for 305 days of lactation, specifically 7900 kg and the total yield of fat and protein - 556 kg. The analysis of reproductive capacity of first-calf daughters of different servicing bulls has shown that the best characteristics were recorded for daughters of Prizer 1347 bull, they had the open period of 72 days and the optimal reproduction rate (1.04). Daughter of Almaz 39 and Megafon 1592 bulls showed the lowest results of reproduction traits, their reproductive capacity rate was 0.80 and the open period was 179 and 180 days, respectively. The breeding farm has built up a unique herd of high performing cows with the annual growth of milk yield of 152 kg per cow. This result has been achieved principally due to the use of young improving bulls in the herd.