Birth defects in first-calf heifers with the use of stud bulls with different index values of “calving ease”

Abstract

In recent years, there has been a tendency to reduce the age of the first insemination of replacement heifers of dairy breeds. However, calving at an early age is often accompanied by complications, which lead to stillborn offspring. In order to reduce the risk of a pathological calving, it is recommended to use stud bulls with an index value of “calving ease” of no more than 2.2 for insemination of heifers of dairy breeds, but there are no objective data on the effect of this index on birth defects. The purpose of our research was to study the calving ease and the stillbirth in offspring of first-calf heifers of three age groups, which were inseminated by bulls with an index of “calving ease” of 1.6 and 1.8-2.1. The difference in the number of difficult calving in favor of first-calf heifers, which were inseminated by stud bulls with an index of “calving ease” of 1.6, was 8.7%. The greatest difference between the experimental groups was at the first insemination at the age of 12-13 months – 29.2%. With an increase in the age of the first insemination, the difference between the experimental groups decreased and amounted to 11.3% at the age of 14-15 months. The minimum difference between the experimental groups was when animals were inseminated at the age of 16-18 months – 5.2%. From using stud bulls with an index of “calving ease” of 1.6, they obtained 9.7% of stillborn offspring, while with an index of “calving ease” of 1.8-2.1 – 17.7%. As for age subgroups, the difference in favor of the animals of the first experimental group, in comparison with the second experimental group, was 5.5%, 4.5% and 10.8%, respectively. The greatest number of difficult calving and stillborn offspring was registered with the first insemination of experimental animals at the age of 12-13 months. This correlation was typical for both the first and second experimental groups.