Estrus synchronization protocols for fixed-time artificial insemination (FTAI) during non-breeding season in ewes

This study aimed to compare three protocols used for induction and estrus synchronization followed by fixed-time artificial insemination (FTAI) during the non-breeding season in anestrous Cluj Merino ewes. Estrus was synchronized in 80 healthy multiparous ewes using intravaginal sponges containing 20mg of fluorogestone acetate (FGA) for 14 days. Ewes were previously divided into three groups. At the time of sponge removal, ewes in groups II and III received a dose of 500 IU eCG, while those in Group I received a half dose, respectively 250 IU eCG, followed by the administration of 50 mu g of GnRH 30 hours later. Ewes from Group III were previously implanted with subcutaneous mini-implants of melatonin, 20 days before progesterone (P4) treatment. We could not find significant differences in terms of reproductive performances between Group I and Group II, with results showing that Group I had a conception rate of 47.05%, which is lower than that of Group II (56.52%). However, there were significant differences (P < 0.05) between melatonin-supplemented Group III and Group I (63.33% vs. 47.05%). Thus, the potential substitution of eCG with GnRH still needs to be optimized, while supplementation with melatonin can increase the conception rate during the non-breeding season in anestrous ewes.