G. Molle

The aim of this presentation is to review some aspects of nutrient utilisation in small ruminants that can affect the reproductive efficiency of females, i.e., oestrous activity, ovulation and embryo survival. Nutrition affects reproduction through short and long-term effects. Body condition affects the onset of anoestrus, the resumption of post-weaning estrus if photoperiod is favourable, and ovulation rate. The positive effect of 'flushing', i.e., supply of energy and protein in excess of requirements for body maintenance, on ovulation rate, is mediated, at least partly, through glucose, amino acid and insulin metabolism. The efficiency of 'flushing' may be impaired by decreased feed intake at pasture, especially if it consists in cereal grain. The 'static' effects on ovulation rate are mediated through modulation of follicular atresia, whereas 'immediate nutrient effects' seem to affect the rate of maturation immediately before ovulation of potentially ovulatory follicles. Provision of excess dietary protein during a few days prior to mating is a potential way to improve fecundity, but effects vary according to source of protein. Too generous a provision or an acute deficit of energy, and overfatting of ewes, reduce progesterone concentration in blood and embryo survival during the first stages of pregnancy. Therefore, 'flushing' must be limited to the pre-mating period, which implies synchronisation of oestrus.