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 Sakız x Karayaka (F2) crossbred sheep. In the first experiment, ewes were allocated into a control group (K, n = 27), and groups administered 4 µg 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 µg 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.

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 Sakız x Karayaka (F2) crossbred sheep. In the first experiment, ewes were allocated into a control group (K, n = 27), and groups administered 4 µg 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 µg 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.