Pituitary responsiveness to GnRH in lambs undernourished during fetal life

A study was conducted to investigate the effect of undernutrition in utero on pituitary responsiveness to GnRH stimulation in lambs after birth. Thirty-four lambs were used which were born to ewes fed 110% of the energy maintenance plus two embryos requirements during pregnancy (control, C) or 90% of the maintenance with no additional allowances for embryo growth (restricted, R) from 30 day of pregnancy to lambing. A GnRH stimulation test was performed on all lambs at 55 days of age. The average energy consumed daily by each ewe in the R group was only the 60% of that consumed by the ewes in the C group. Following injection of GnRH, peak LH values were observed within 15 min in both groups, Animals in Group C (n = 19) showed a significantly greater LH response than animals in Group R (n = 15) at 15 min and at 30 min post-injection (43.3 vs. 33.9 and 39.0 vs. 32.2 ng ml(-1), respectively). The significant treatment x time interaction found revealed that the rate of increase of LH concentration above the basal value within the first 15 min after GnRH administration was higher in C than in R lambs, while the rate of decrease from 30 to 120 min was lower in R than in C lambs. It was concluded that the timing as well as the magnitude of maternal undernutrition may be significant factors affecting the subsequent reproductive potential of the progeny in sheep by reducing pituitary activity.