The effect of short-term nutritional supplementation and body condition on the pituitary and ovarian responses of anoestrous ewes to the “ram effect”

Abstract

In sheep production, the “ram effect” is a technique for inducing fertility in seasonal anoestrus and “flushing”, another technique to increase litter size. Often used individually, we wanted to know if they could be used together to improve reproductive performance of ewes bred during the anoestrus season. Two experiments were conducted; the first with Île-de-France ewes (N=30) comprised a control and a group fed a nutritional supplement and the second with Romane ewes (N=60) replicated these treatments at two levels of body condition. The ewes were stimulated with the “ram effect” and the following responses measured (i) blood concentrations of LH, FSH, oestradiol, progesterone, glucose and insulin (ii) oestrus. Supplementation increased blood glucose and insulin in experiment 1 but not in experiment 2 but it had no effect on FSH; it reduced oestradiol in experiment 2 but not in experiment 1. Higher body condition was associated with higher blood glucose and insulin but not FSH or oestradiol. In addition, higher body condition was associated with a greater proportion of ewes responding to the “ram effect” and greater short-term responses for LH and oestradiol; supplementation had no effect on these responses. In experiment 1 but not experiment 2, supplementation was associated with a higher proportion of ewes in oestrus. The results demonstrate that there are close relationships among the concentrations of LH and oestradiol, the LH surge and the ovarian cyclicity in response to the “ram effect”. These data show an effect of body condition on the “ram effect” that can modify cyclicity and suggest an effect of short-term nutritional supplementation on oestrus. Furthermore these data also suggest that the functional capacity of follicles at the time of the “ram effect” is an important determinant of outcome.