Experiments were carried out to test the effects of maternal nutrition (0.5 versus 1.0 x maintenance) during early foetal life and peri-ovulatory nutrition on the reproductive performance and associated parameters of Scottish hillbreeds (North Country Cheviot and Scottish Blackface) crossed with Texel sires carrying or not carrying the X-linked Inverdale (FecX^I) gene. Undernutrition of the dam resulted in reduced birthweights of single male lambs, reduced plasma progesterone concentrations of ewe lambs and a tendency for reduced ovulation rates in ewe lambs and shearlings (non-carriers) but litter size was not affected. Heterozygous carriers of the Inverdale gene showed a mean increase in ovulation rate of approximately 0.35 as ewe lambs, and approximately 0.65 the following year, the latter resulting in a mean litter size increase of approximately 0.6. Plasma progesterone concentrations were lower for FecX^I gene-carriers as ewe lambs and also as adults in a flock that had been flushed prior to mating, suggesting that the increased feed intake could have had a suppressing effect on the concentrations of this hormone. It is postulated that this could have resulted in the large number of peri-natal losses associated with gene-carrier ewes in the same flock, since neonatal vigour of offspring of gene-carriers was not affected in the SAC experimental flock that had not been flushed pre-mating. Presence of the FecX^I gene is associated with a reduction in birthweight of approximately 0.5 kg which could be due to the reduced placental efficiency of gene-carrier dams. At puberty and as shearlings gene-carriers remained lighter than their non-carrier counterparts. Throughout the shearling breeding season the increase in ovulation rate associated with this prolificacy gene remained constant.