Administration of gonadotropin-releasing hormone at sponge insertion increases litter size in ewes subjected to a fixed-time insemination procedure

ABSTRACT The effect of a dose of GnRH administration at sponge insertion on pregnancy rate and litter size in ewes was investigated. A total of 162 pluriparous, non-lactating Huyang ewes (3–4 years old, 40–50 kg body weight, 120–150 days postpartum) were randomly and equally assigned to three groups (n = 54 each): control, G25, and G50. Estrus was synchronized using an intravaginal sponge impregnated with flurogestone acetate for 12 days, followed by an injection of 330 IU of equine chorionic gonadotropin at sponge removal. At sponge insertion, ewes received an intramuscular injection of either 25 µg (G25) or 50 µg (G50) of the GnRH agonist triptorelin, or saline solution (control). Fixed-time artificial insemination was performed at 52 and 60 h after sponge removal. Pregnancy was diagnosed by transabdominal ultrasonography 45 days post-insemination, and reproductive parameters were recorded after lambing. Pregnancy rate was not affected by GnRH administration (P = 0.3001). However, the multiple birth rate (P = 0.0032) and litter size (P = 0.0012) were significantly increased in the G50 group compared with control. In conclusion, administration of 50 µg of GnRH at sponge insertion increased litter size in Huyang ewes subjected to fixed-time artificial insemination.