Effects of undernutrition in utero and in early life on development and function of the reproductive axis in female sheep
Experiments were designed to determine: a) The effect of undernutrition in utero and in early post-natal life on subsequent activity of the hypothalamic-pituitary-ovarian axis in prepubertal and peripubertal female sheep; b) The effect of undernutrition in utero from the time of mating on development of the ovaries of foetal female sheep at days 47 and 62 of gestation. It is concluded that undernutrition in early life significantly retards pituitary development as demonstrated by the selective hypersensitivity of prepubertal L group pituitary glands but that this is compensated for around 18 months of age, by which time peripubertal L group pituitary glands are hyposensitive to positive GnRH stimulation. As there were no effects of treatment on metabolic hormone profiles or glucose clearance rate, it can be concluded that undernutrition acts directly at the pituitary level and not through differences in L group metabolism. In experiment 2, ewes were fed 150% (High; H) or 50% (Low; L) of maintenance energy requirements from mating until 47 or 62d of gestation in separate studies. At 47d, L lambs exhibited normal foetal weight, foetal ovarian weight and foetal ovary steroidogenic capacity but had significantly retarded germ cell degeneration as indicated by higher concentrations of oogonia in L group foetal ovaries (p<0.001). At 62d, L lambs exhibited significantly retarded germ cell degeneration, as indicated by higher oocyte concentrations (p<0.01), and delayed arrest of meiosis, as indicated by higher meiotic activity (p<0.001). It is concluded that undernutrition of the ewe from the time of mating significantly retards ovarian development in foetal ovaries. This retardation may be responsible for the known reduction in lifetime reproductive performance of ewes undernourished in early life.