Reproductive features and quality of milk of the golstinized heifers of black-and-white breed in OJSC "Orlovskoe"

The aim of this work was to study the reproductive features and quality indicators of milk of black-and-white cows in the OJSC "Orlovskoye" of the Oryol region. The studies were conducted in 2016-2018 in OJSC "Orlovskoye of the Oryol region. The object of the research was the first heifers of the black-and-white breed, obtained as a result of cross-breeding the stock of the farm with the stud bulls of the leading Holstein lines. The age of the first insemination of half-breeds and 3/4 heifers was almost the same from 19.4 to 19.6 months. The youngest for the first insemination were the heifers of the Holstein half-breed, they were younger by 0.3-1.9 months compared with other heifers. Live weight at the first insemination had a positive correlation with age. Thus, Holstein half-breed heifer, the oldest for the first insemination, had the largest live weight of 377 kg, and 3/4 Holstein heifers, the youngest for the first insemination had the lowest live weight of 366 kg. Holstein half-breed heifers have the best reproductive features. Holstein blood affects the length of the postpartum recovery period of sexual cyclicity. By the animals of different blood levels in the Holstein breed, the duration of the parameters of the estrous cycle is different. Thus, in half-blooded heifers, the duration of estrus was significantly shorter than that of 3/4-blooded heifers - by 18.2% and, was shorter than the time from the start of estrus to follicle ovulation - by 6.7% accordingly. According to the indicators of physicochemical properties, the milk of heifers of different Holstein blood levels did not reveal significant differences and corresponded to the requirements of GOST 31449-2013 - Raw cow milk.