Effect of Enhanced Uterine Involution on Reproductive Performance in Multiparous Ewes

Rapid uterus involution is essential for minimising interpartum intervals, enhancing reproductive performance, and optimising production in ewes. This study aimed to accelerate the uterine involution of postpartum ewes through a relatively simple hormone treatment approach. In this study, 96 Dorper × Hu F1 ewes were assigned to three groups. The ewes were subsequently injected with normal saline (control group), prostaglandin + oxytocin (PG + OT group) and prostaglandin + oxytocin + horse chorionic gonadotropin (PG + OT + eCG group). Each group had 16 ewes producing a single lamb and 16 ewes producing twin lambs used to determine the effects of different treatments on their uterine involution and reproductive performance. PG + OT + eCG treatment accelerated the rate of uterine horn involution of single lambs (21.40 ± 0.89 days vs. 30.66 ± 1.03 days, p < 0.05) and twin hlambs (22.2 ± 1.09 days vs. 30.33 ± 0.81 days, p < 0.05) compared to the control group. PG + OT + eCG treatment also accelerated the regression of the uterine wall serosa structure and the removal of uterine effusion compared to PG + OT treatment, whose effect was moderate. PG + OT and PG + OT + eCG treatments had no significant effect on the recovery of the maximum uterine diameter of single and double lambing ewes compared to the control group. However, both treatments shortened the first estrus time of postpartum ewes (53.73 ± 3.69 days vs. 48.06 ± 5.87 days vs. 46.46 ± 7.41 days, p > 0.05). There was no significant difference in the conception rate among groups (p > 0.05). Notably, the change trend of reproductive hormones in postpartum ewes was consistent. PG + OT and PG + OT + eCG treatments significantly increased the concentration of estradiol and follicle-stimulating hormone during uterine involution (p < 0.05), but inhibited the secretion of progesterone compared to the control group. The peak of the luteinising hormone in the two treatment groups appeared 14 days earlier compared to that of the control group. In summary, exogenous PG + OT + eCG increases the concentration of estradiol during uterine involution, inhibits the secretion of progesterone, and accelerates the postpartum uterine involution and postpartum estrus time of ewes. These findings provide a basis for exploring the mechanism of uterine involution in sheep and improving sheep production efficiency.