The ram effect : an up-to-date method for the control of oestrus and ovulation in sheep

Abstract

The introduction of rams in a group of anoestrous females induces a silent ovulation (without oestrus) within 2 to 4 days. This silent ovulation is followed either by an ovarian cycle of ’normal’ duration (around 17 days) and a new ovulation time which is associated with oestrous behaviour, either by an ovarian cycle of short but constant (6 days) duration followed by a new silent ovulation and, after an ovarian cycle of normal duration, by and oestrus and ovulation.

As a result, in female induced to ovulate, the first oestrus are observed either 18 to 20 days or 24 to 26 days after introduction of the rams in the flock.

Following mating, non pregnant females may return to oestrus except if the intensity of anoestrus is too strong at the time of these oestrus which are expected 1 to 1.5 month after the induced ovulation.

The point is made on the underlying physiological mechanisms involved in the process of this induction of ovulatory and oestrous activities by the ram effect. Practical rules for management of flocks that want to use this up-to-date technique of control of ovulation and oestrus in sheep are also given. The two main points are firstly the knowledge of seasonal variations of reproductive activity of females in their environment which determine the period of efficiency of the ram effect and, secondly, the opportunity and facilities to separate rams and females for a minimal period of one month before their physical contact for the ’ram effect’.