Undernutrition of ewe lambs in utero and in early post-natal life does not affect hypothalamic–pituitary function in adulthood

The effect of undernutrition in utero, during late gestation (from day 100), and early neonatal life on hypothalamic–pituitary function was investigated in female lambs born to ewes fed rations calculated to provide either 100% (high; H) or 70% (low; L) of the energy requirements to sustain a twin pregnancy. Following parturition in early spring, ewes and lambs were maintained on pasture with sward heights of 6 cm (H) or 4 cm (L) until week 8 of lactation and then sward heights of 5 cm (H) or 3 cm (L) until weaning at week 14. Mean lamb birth weights were 18% lower in L than H animals (P<0.05) and mean liveweights were 23% lower in the L animals (P<0.001) at weaning at 14 weeks of age. Liveweight differences were not significant at, or after, 26 weeks of age. There were no significant differences between pre-pubertal H and L animals, either before (26 weeks) or after ovariectomy (31 weeks), with respect to hypothalamic or pituitary activity, as measured by LH pulse frequency, pulse amplitude or mean plasma LH and FSH concentrations and the responses to GnRH injection as measured by LH peak amplitude, respectively. Similarly there were no differences in any of these variables in pubertal animals at 18 months of age. At 31 weeks of age, H animals had significantly lower pituitary GnRH receptor binding (P<0.01) and lower ER(alpha) mRNA content (P<0.05) than L lambs. There were no differences with treatment in the abundance of mRNA for LH(beta), FSH(beta) or GnRH-receptor at 31 weeks of age or in pubertal animals aged 18 months, when there were no significant differences with treatment in GnRH receptor binding or ER(alpha) mRNA expression. It is concluded that effects on lifetime reproductive function of female sheep of undernutrition during late gestation and early neonatal life are unlikely to be expressed through permanent changes in hypothalamic–pituitary function and are therefore attributable to effects exerted directly on the ovary.