Effects of oestrus induction with progestagens or prostaglandin analogues on ovarian and pituitary function in sheep

The aim of the current study was to determine possible differences in ovarian and pituitary features explaining lower fertility rates in sheep with oestrus induced with intravaginal progestagens or prostaglandin analogues (group FGA and PGF, n = 8 in both) when compared to a control group (group C, n = 8). The growth profiles and the mean individual sizes of preovulatory follicles were similar between groups; however, the number of preovulatory follicles per ewe and, consequently, the number of ovulations were higher in groups FGA and PGF (2.3 ± 0.3 and 2.0 ± 0.1, respectively) than in group C (1.4 ± 0.1, P < 0.05). However, plasma oestradiol concentrations were similar between groups suggesting a defective function in some preovulatory follicles of groups FGA and PGF. In group FGA, the basal LH levels during the follicular phase were lower (0.21 ± 0.0 ng/mL, P < 0.005) than in groups C (0.41 ± 0.1 ng/mL) and PGF (0.55 ± 0.1 ng/mL); the onset of preovulatory discharge being later (21.0 ± 2.3 h vs. 12.8 ± 1.5 in C and 14.5 ± 1.5 in PGF; P < 0.05 for both). Finally, luteal activity was also found to be affected in group FGA; the rate of progesterone secretion per total luteal tissue was lower (range: 0.46–0.65 ng/mL/cm2) than in ewes treated with cloprostenol (2.1–3.3 ng/mL/cm2) and control sheep (2.0–3.4 ng/mL/cm2).