Supplements of dietary fat are highly effective in boosting energy intake at critical phases during the reproductive cycle. When fed to ruminants in the form of calcium salts of fatty acids, they have been shown to increase plasma cholesterol and progesterone levels (Spicer et al, 1993) which, in turn, could have beneficial effects on ovulation rate and embryo quality. In sheep, a likely reproductive state for a physiological response to a lipid supplement is during the superovulation of young animals in which the post-ovulatory steroidogenic capacity of the corpora lutea may be sub-optimal. The present study examined the effects of donor age and dietary fat on plasma progesterone concentration, and the yield and quality of embryos in superovulated Cheviot sheep.