The effect of gonadotropin-releasing hormone after a short-term synchronisation protocol on fertility in Assaf sheep during the breeding season

This study aimed to evaluate the effect of gonadotropin-releasing hormone (GnRH) administration 48 hours after progesterone-impregnated sponge removal on fertility and prolificacy in lactating Assaf ewes. In this study, 71 ewes were synchronised using intravaginal sponges containing 60 mg medroxyprogesterone acetate for six days. On the day of sponge removal, all ewes received 500 IU of equine chorionic gonadotropin and 75 µg of d-cloprostenol. In the control group (n = 35), ewes were injected with 1 mL of physiological saline solution; in the GnRH group (n = 36), ewes were injected with 0.1 mg of GnRH analogue 48 hours after sponge removal. There were no significant differences between the groups in the progesterone concentration, oestrus response, oestrus duration, onset of oestrus, abortion rate, lambing rate, multiple birth rate, and fertility results. However, the pregnancy rate differed between the groups, being significantly lower in the GnRH-injected ewes (69.44%) than in the control ewes (91.42%). The lambing rates were 90.62% and 96.0% in the control and GnRH ewes, respectively. The results of this study suggest that GnRH administration 48 hours after progesterone-containing sponge removal enhances prolificacy in lactating Assaf ewes during the breeding season, and it was concluded that prolificacy rates could be improved with post-synchronisation GnRH administration. However, pregnancy rates would need to be increased using different supportive treatments. (Submitted 11 July 2025; Accepted 06 December 2025; Published 14 January 2026)