Optimal reproductive period of use of bulls and cows of black-and-white breed
It was determined the optimal reproductive period of use in 4 bulls for 8 years and cows (n=302) black-and-white breed, from the first to the ninth lactation, with productivity of 4500-8500 kg of milk per lactation. It was investigated 5109 ejaculates and taken into account in 2496 calving. It was found that the most active reproductive age of bulls is up to 7 years. The active period of use (aged 3-5 years) defect seed was 3.1-5.3%, the amount of seed was 4.8-5.8 ml per bull, the highest number of sperm was 15-16 billion per ejaculate. The maximum average for the total number of sperm per ejaculate revealed at the age of six years and was 8.1 billion. The number of doses of frozen semen to ejaculate were obtained from animals older age (6-8 years) and got 208-248 doses, respectively. Optimal reproductive period, long-lived cows observed from the first to the sixth lactation. More than half of the cows from the first to the sixth lactation had service period less than 100 days. Beginning with the seventh lactation number of cows with less than 100 days of service reduced by 5-10% annually, and in the 9th has already reached 33%. The number of animals with the service period of 101-150 days regardless of lactation averaged 21-24%, except in the 7th and 9th lactation, in which these animals was more by 7-10% for each of the previous lactation and was 29-31%, respectively. The number of cows with critical indicators of the service period (over 201 days) amounted to only 6.6-10.0% from the first to the third lactation. Since the fourth lactation number cows increased by 2-3% with each subsequent lactation, and in the 9th lactation already reached a level of more than 20% (2-3 times more). It was established that the process of reproductive aging in black-and-white cattle regardless of sex of animals begins with 8-year life under normal conditions of housing, feeding and harnessing