THE DYNAMICS OF SOME REPRODUCTIVE PERFORMANCE PARAMETERS IN COWS WITH DIFFERENT LACTATION PERSISTENCY INDICES

russe. This article presents working material on the dynamics of changes in reproductive traits in cows with different rates and intensity of lactation. Animals of different genotypes were divided into two groups with different lactation persistency indices. Preliminary statistical analysis of some indices of reproductive traits was carried out for 246 Holstein cows for a number of lactations. The reproductive qualities of the cows were evaluated taking into account: age of the first insemination and age of the first calving, duration of the service-period after the second and third lactations and the duration of the calving interval connected with this indicator. It was found that cows with different lactation persistency index were inseminated at a certain age. The drying period was 65 days for cows with lactation persistency index after the second calving, only one day later the cows with lactation persistency index more than 100% went to lactation. Duration of the dry period after the third lactation ranged from 68 to 71 days. The duration of the service period of cows in the first group after calving was 132 days, which was 16 days shorter than that of cows in the second group, – 148 days (P>0.99). (Р> 0,99). After the next calving we note increase of the service-period in cows with lactation constancy index more than 100% up to 154 days. Using the lactation persistency index as an additional test when selecting cows for a promising uterine herd, it is possible to give a more complete evaluation of the potential of reproductive traits of cows. The lactation persistency index can be recommended when selecting cows in the higher breeding group.