Variation in the timing of ovulation relative to other follicular phase events following natural and induced luteal regression in dairy cows

Abstract

Insemination at an inappropriate time is one of many constraints to good fertility in dairy cows. As a result, many studies have attempted to improve the synchrony of oestrus in controlled breeding programmes. However, the success of insemination depends not merely on the detection of oestrus, but also on the timing of ovulation relative to insemination. Thus a better understanding of the factors associated with the precise timing of behavioural oestrus and ovulation is required. In this study the time of ovulation has been determined, by ultrasound scanning, in relation to a variety of follicular phase events in dairy cows following both natural luteolysis and luteolysis induced by treatment with a prostaglandin F2a analogue. The objectives were firstly to determine whether differences existed in the timing of follicular phase events following natural and induced luteal regression and secondly to determine the degree of variation that exists between the timing of ovulation and the timing of other follicular phase events.