The effect of GnRH administration on plasma progesterone and reproductive performance in ewes

Two experiments were carried out to investigate the effect of GnRH administration at mating and on day 12 post-mating on the reproductive performance of Karayaka and Sakiz x Karayaka (F-2) crossbred sheep. In the first experiment, ewes were allocated into a control group (K, n = 27), and groups administered 4 mu g GnRH at mating (A, n = 27), on day 12 post-mating (AS, n = 30) and both at mating and on day 12 post-mating (AAS, n = 30). GnRH administration in the A and AS groups increased plasma progesterone concentrations (P < 0.01). The pregnancy rate at first mating in the AS group (86.7%) was higher than those in the ASS (66.7%), A (51.9%) and K (51.9%) groups (P < 0.01). There was no difference between the treatment groups in terms of litter sizes (1.31, 1.21, 1.21 and 1.20 for AS, K, A and ASS, respectively). In the second experiment, ewes were allocated into 2 groups, a control group (K, n = 70) and a group administered 4 mu g GnRH on day 12 post-mating (AS, n = 73). The pregnancy rate at first mating was 71.4% and 80.8% (P > 0.05) and litter size was 1.24 and 1.53 (P < 0.01) for K and AS, respectively. In conclusion. GnRH administration on day 12 post-mating can increase the litter size and pregnancy rate in ewes.