The influence of outbreeding and inbreeding on the results of calving of black-and-white cows with an average percentage of Holstein genes (HF) of 49.3-60.2%

In the selection of dairy cattle there is currently a problem of the spread of inbreeding. To study the influence of inbreeding on reproductive qualities in the Oryol region, these studies were conducted. It was established that during the analyzed period, 1052 calves were obtained from 5 calvings, of which 42.2% (444 heads) were heifers. According to the first calving, 271 heads of young animals (or 62.6%) out of 433 heads were inbred. Among the outbred herd, 44.4, 37.8, 41.7, 37.5 and 41.9% of heifers were born from the first to the fifth calving, respectively (41.3% of all 424 heads were heifers), for the inbred herd from the first to the fifth calving this figure was 46.5, 48.9, 37.2, 44.1 and 53.8%, respectively (45.7% of all 588 heads were heifers, which exceeded outbreeding by 4.4%). The highest percentage of twins was obtained for the fourth calving - about 14% of all analyzed calvings, although for the first calving it was about 0.2%. With inbreeding, 6.5% of the calves were twins, with outbreeding - 3.8%. In outbreeding, there were 12 stillborn calves for all calvings, in outbreeding - 29 dead calves, which amounted to 2.75 and 4.70%, respectively, but the largest number of dead calves was obtained with inbreeding for the first calving - 21 heads, or 7.2% of the total number of calvings. Therefore, inbreeding has a negative effect on reproductive qualities, but inbreeding leads to an increase in the percentage of heifers at calving and twins. These results should be taken into account when planning selection and unjustified inbreeding should not be allowed, since it is capable of changing the results of selection and selection at the population level.