Analysis of the calving-to-conception interval variation and it relation to milk production traits of dairy cows

Abstract

Intensive selection for milk production has resulted in unfavorable genetic correlations with fertility, contributing to longer calving intervals, increased insemination rates, higher culling levels, and rising costs of reproductive management. This study e x amined the effects of genetic and environmental factors on the calving-to-conception interval and its relationship with milk produ c tivity traits in Holstein cows. The analysis was based on data from cows that calved at PJSC ‘Plemzavod Stepnoy’ in Zaporizhzhia region , Ukraine , between 2014 and 2017. For each animal, 305-d milk yield, milk fat percentage, and the calving-to-conception interval were recorded and analyzed using the General Linear Model. The results showed that parity, year and season of calving significantly influenced the calving-to-conception interval, whereas the effect of sire was not significant. Younger cows generally conceived sooner after calving than older cows. Over the study period, there was a clear tendency toward shorter calving-to-conception intervals, suggesting improvement in reproductive performance. Cows calving in summer and autumn also had shorter intervals than those calving in winter or spring. The joint analysis of parity and the calving-to-conception interval indicated that reproductive efficiency was closely related to milk yield and composition. Cows with moderate calving-to-conception intervals (91–120 d) produced more milk of slightly higher quality than those with shorter or longer intervals. Overall, the findings highlight the importance of managing reproductive cycles to optimize both fertility and milk productivity in Holstein herds under the produ c tion conditions of southern Ukraine.