The effect of males on female reproductive physiology

In a variety of situations (at puberty, during seasonal or lactational anoestrus, or during cycle itself), the male's presence induces ovulation. In the domestic sheep, it could be used as a practical way to control reproduction. in some breeds such as Merino, a double peak of fertile oestrus is observed 20-25 days after introduction of the ram. A silent ovulation occurs 48 hours after the presentation of the male. This is the consequence of a change in pulsatile release of LH occuring as early as within some minutes. The corpus luteum does not develop normally resulting in a short cycle of ca 5-7 days. It is at the 2nd or 3rd ovulation that sexual receptivity is observed. In other breeds, such a reaction cannot he elicited during the middle of the seasonal anoestrus. The mechanisms invole chemical stimuli, but the identification of the chemical signal has not vet been realized. The presence of abnormally short cycles can he eliminated by a progestagen treatment, even reduced to a single injection. In the practice, such a treatment gives a normal fertility in synchronizing within 2-3 days the majority of the oestrus, allowing the use of artificial insemination.