Effect Of Different Litter Size And Drugs On Uterine Involution In Primiparous Hu Sheep

Objective:At present,the feeding mode of the sheep industry changes from free-range feeding to intensive house feeding,and multiparous and perennial estrous Hu sheep have become excellent house feeding sheep breeds.In order to make the Hu sheep production system reach two years and three births,it is necessary to enter the next reproductive cycle as soon as possible after delivery,which also has certain requirements for the time of uterine involution in Hu sheep.Therefore,it is of great practical significance for ewes to complete uterine involution as soon as possible after delivery to restore their reproductive performance,shorten lambing interval and improve fertility.In this study,we first diagnosed the early pregnancy of newborn Hu sheep by rectal B ultrasound,combined with the effects of different litter size,cloprostenol and oxytocin on uterine involution in newborn Hu sheep,and also measured the changes in the serum concentrations of P₄,LH,FSH,and E₂during uterine involution in different treatment groups using ELISA,and observed and recorded the days of the first estrus after delivery and the conception rate.Methods:（1）80 primiparous Hu sheep were diagnosed for early pregnancy by rectal ultrasound on days 20,25 and 30 after natural mating to determine the optimal time for early pregnancy diagnosis.（2）60primiparous Hu sheep were divided into Group A,singleton parturition（n=20）;Group B,twin parturition（n=20）;and Group C,triplet parturition（n=20）.The changes of uterine horn diameter and maximum uterine caruncle diameter within 45 days after delivery were recorded by B ultrasound rectal examination.To compare the effects of different litter sizes on uterine involution in primiparous Hu sheep.（3）90primiparous Hu sheep were treated with different drugs within 12 h postpartum.They were divided into singleton parturition group（n=30）,twin parturition group（n=30）and triplet parturition group（n=30）according to the number of lambs;singleton parturition ewes were further divided into control group（3 ml0.9%sodium chloride,n=10）,PG group（0.2 mg cloprostenol,n=10）and PG+OT group(0.2 mg cloprostenol+10 U mikacin（n=10）,and the twin parturition group and triplet parturition group was equally divided.Changes in uterine horn diameter and maximum uterine caruncle diameter were monitored regularly with B-mode ultrasound within 0-45 d postpartum.At the same time,jugular vein blood samples were collected from postpartum ewes every 5 d from 0-60 d after delivery,and then the concentrations of reproductive hormones P₄,LH,FSH,and E₂were measured by ELISA kits,and the days of the first estrus and conce _Ption rate of ewes after delivery were observed and recorded.Results:（1）In the early pregnancy diagnosis by rectal ultrasound on days 20,25,and 30 after breeding in Hu sheep,clearer embryo image maps could be observed on day 30,when the pregnancy diagnosis rate was high.（2）The higher the number of lambs the slower the rate of uterine involution.Singleton parturition ewes completed uterine involution on the 30th day postpartum,while triplet parturition ewes had the slowest rate of uterine involution,most of which were completed on the 40th day postpartum.There was no significant difference in the maximum diameter of uterine caruncle among singleton parturition,twin parturition and triplet parturition ewes（P>0.05）.（3）PG+OT can promote the recovery of the postpartum uterus.The mean rate of uterine involution was faster in ewes with single lambs（26.13±0.68 d）than in ewes with three lambs（33.8±1.12 d）.Among the single-lamb ewes,the PG+OT group had the fastest rate of uterine involution,with an average completion time of 22.8±4.5 d,which was significantly earlier than the control group uterine involution time（40.17±0.35 d）among the three-lamb ewes（P<0.05）.Combined with ELISA to determine the reproductive hormone concentration during uterine involution,it was found that the first peak of LH（30 d Vs 35 d Vs 35 d）and E₂（25 d Vs 30d Vs 30 d）appeared earlier in the PG+OT group than in the control and PG groups,the first peak of FSH（25 d Vs 15 d Vs 15 d）appeared later in the control group than in the PG+OT group,and the first peak of P₄（25 d Vs 30 d Vs 30 d）appeared earlier in the control group than in the PG+OT group;PG+OT promoted the secretion of LH,FSH and E₂and inhibited the secretion of P₄.The days of the first estrus after delivery in the PG+OT group were significantly earlier than those in the control group（47.8±2.22d Vs 50.6±1.92 d Vs 55.6±3.27 d）,and the conception rate within 60 d after delivery in the PG+OT and PG group was higher than that in the control group but the difference was not significant（P>0.05）.Conclusion:（1）Through rectal ultrasound pregnancy diagnosis,on the 30th day after breeding in Hu sheep is the best time for early pregnancy diagnosis.（2）The higher the number of lambs the slower the rate of uterine involution,and the rate of uterine involution is faster in single-lambed ewes than in three-lambed ewes.（3）PG+OT contributes to uterine involution,promotes the early secretion of LH,FSH,and E2,and inhibits the secretion of P₄;it also shortens the days of the first estrus after delivery.