Overfeeding during early pregnancy compromises pregnancy establishment and /or embryo survival in a variety of domestic species including sheep, cattle and pigs (reviewed by Robinson, 1990). Embryo survival was reduced in recipient ewes receiving a high as opposed to a low plane of nutrition from embryo transfer on day 5 post-ovulation to day 60 of gestation (McKelvey & Robinson, 1988).Similarly high plane feeding for only 12 days starting on day 2 after mating significantly reduced pregnancy rates at day 60 ( Parr et al .,1987). Although not extensively monitored in either study, peripheral progesterone concentrations were inversely correlated with feed intake. Indeed, the reduction in pregnancy rate in high plane ewes in Parr's study was reversed by progesterone supplementation on days 8-14 after mating.The inhibition of luteolysis and maintenance of adequate progesterone secretion by the corpus luteum is central to the maternal recognition of pregnancy in sheep ( Bazer et al .,1991 ). Progesterone plays a major role in controlling maternal secretion of nutrients, growth factors , immunosuppressive agents .enzymes and steroids required for successful embryo development. It seems likely therefor that the mechanisms underlying nutritionally induced differences in pregnancy rate and embryo survival may operate via changes in progesterone levels which in turn alter the secretory dialogue between the conceptus and its maternal environment.