Associations of fertility indicators of breeding Ayrshire cows in the conditions of the European North of Russia

The fertility of cows as the ability to produce offspring has a fundamental importance for optimizing the reproduction of the herd in dairy cattle breeding. With the increase in the value of milk yield in modern cows up to 8–10 thousand kg of milk and more, their reproductive abilities deteriorate. Objective: identification and characterization of associations of fertility indicators, their relationship, dependence on the level of milk yield in Ayrshire cows. Materials and methods. The research was held on cows of the Ayrshire breed of the breeding plant «Megrega» (Republic of Karelia). The average milk yield per cow is over 9000 kg of milk per year. Fertility indicators were taken into account for 5 years according to 3866 lactation data. The interrelations of these indicators and their associations with the value of milk yield were analyzed. Results . The age of the cows did not significantly affect on the fertility parameters, which were almost the same from the first to the fifth calving. An increase in the milk yield during the current lactation had a significant worsening effect on reproductive characteristics. The increase in milk yield from 5000 kg to 10000 kg and more was accompanied by an increase in their the indifference period (IP) by 38.4; the period of insemination (PI) – by 50.5; the service period (SP) – by 88.9 days; number of inseminations per conception – conception index (CI) – from 1.25 to 2.27; early embryonic death (EED) – from 3.1 to 13.3 % (P<0.001); fertilization from the first insemination – conception rate (CR) decreased from 78.1 to 33.6 %. The period from calving to the first insemination plays a special role among all fertility indicators. The best fertility rates were recorded in cows with an indifferent period of 100–120 days. A positive correlation was established between milk yield and IP (r = + 0.11–0.18, Р<0.001). Conclusions. The obtained results can be used in further research on the development of breeding indices, the selection of which can provide a high genetic trend in milk yield while maintaining and developing progressive fertility of dairy cows.