Experimental Study On Efficient Reproduction Technology And Reproductive Hormone Monitoring Of Tan Sheep

As a unique sheep breed in China,Tan sheep is mainly distributed in Ningxia and its surrounding areas,and it is a"hematopoietic industry"for Ningxia to get rid of poverty and become rich.However,due to the reproductive characteristics of Tan sheep,such as seasonal estrus,one child per year and one lamb per child,the production efficiency is low.At the same time,with the change of feeding mode,the breeding cost has increased greatly.Under this background,it is necessary to greatly improve the reproductive efficiency of Tan sheep raised in house,increase economic benefits and promote the benign development of Tan sheep industry.In this experiment,we observed the natural estrus law of lambs in lactation and weaning in spring and autumn,and monitored the reproductive hormones in peripheral blood to clarify the estrous situation and endocrine changes of ewes in different seasons after delivery.On this basis,the experimental research and application of the same estrus in empty pregnant ewes,induction of estrus in early weaning ewes,artificial insemination of estrus ewes,breeding and early weaning of lactating lambs were systematically carried out.To establish an efficient reproductive technology system for Tan sheep suitable for production and application,in order to shorten the reproductive cycle and improve the reproductive efficiency of ewes,and to provide reference for screening and optimizing the treatment scheme by monitoring the reproductive hormones of ewes treated by estrus synchronization and estrus induction.The contents and results of the experimental study are as follows:1.Observation of natural estrous regularity and endocrine monitoring of spring and autumn lambs during lactation and after weaning.No estrus was observed during postpartum lactation in spring,and only 6.89%（2/29）of ewes were naturally in estrus after weaning.In autumn,96.43%（27/28）ewes had natural estrus during postpartum lactation,and 3.57%（1/28）ewes without estrus during lactation had natural estrus after weaning.The monitoring results of reproductive hormones in peripheral blood during postpartum lactation in spring and autumn showed that the changes of reproductive hormones during postpartum lactation in spring were stable without obvious fluctuations.In autumn,the reproductive hormone levels of postpartum ewes fluctuated obviously about 18 days after delivery.The monitoring results of reproductive hormones in the peripheral blood of oestrus ewes after weaning in spring showed that the levels of follicle-stimulating hormone（FSH）,Luteinizing hormone（LH）and 17β-estradiol（17β-E₂） increased slightly after weaning,and there was no obvious peak.Progesterone（P₄）and Prolactin（PRL）levels remained high from weaning to the end of sampling.The results of peripheral blood reproductive hormone monitoring of estrous ewes after weaning in autumn showed that the level of FSH increased before estrus and decreased at the end of estrus.LH level gradually increased after estrus,and reached the peak before the end of estrus.The 17β-E₂ level gradually increased after estrus,reached the highest value at about 36 hours,and then decreased.P₄ level was the lowest during estrus,increased briefly during estrus and then decreased.PRL levels increase before oestrus,fluctuate during oestrus,and decrease in concentration before the end of oestrus.2.Estrus synchronization,endocrine monitoring and reproduction test of Tan sheep.In autumn,173 pregnant ewes were treated with progesterone vaginal sustained-release agent（Common name CIDR）+gonadotropin（GTH）+cloprostenol sodium injection（PG-Cl,hereinafter referred to as PG）and PG+PG+GTH respectively.Among them,GTH can be divided into three types:pregnant horse serum gonadotropin（PMSG）,follicle stimulating hormone（FSH）and human menopausal gonadotropin（HMG）.The estrus synchronization rates of the treatment schemes with progestogen and prostaglandin were 89.66%and 90.70%,respectively,with no significant difference（P>0.05）.The two treatment schemes were supplemented with PMSG 500（rat unit）,FSH 50（mouse unit）and HMG 125（rat unit）,and the total pregnancy rate of ewes was the best when PMSG 500 was used.The results of reproductive hormone monitoring showed that the contents of FSH,LH,17β-E₂ in peripheral blood of sheep were significantly higher than those before GTH injection,and the contents of P₄ were significantly lower（P<0.05）.In the prostaglandin-based regimen,the contents of FSH,LH,17β-E₂ in peripheral blood of sheep were significantly increased and P₄ was significantly decreased 2 days after the second injection of PG（P<0.05）.And the fluctuation range of different hormone contents among different individuals is obviously reduced,reaching a relatively consistent level,which is consistent with the concentrated estrus phenomenon at corresponding time points.3.Estrus induction,endocrine monitoring and reproduction test in early spring lambing weaned ewes.When CIDR combined with GTH was used to induce estrus in early weaning ewes at different times（0-3 d after weaning or 7 d before weaning）,the estrus rate of 0-3 d after weaning group（82.67%）was higher than that of 7 d before weaning group（67.12%）.The pregnancy rate was 82.00%and 73.97%,respectively,and the difference was not significant（P>0.05）.In the two treatment schemes,the pregnancy rate was higher by using PMSG as an auxiliary treatment.During the treatment period,the levels of FSH and LH in peripheral blood of each group decreased slowly,and reached the lowest level when the plug was removed,while the level of 17β-E₂ increased slowly and reached the peak when the plug was removed.During estrus,FSH and LH increased rapidly after estrus,reached the peak at 24 h,and then decreased.The level of 17β-E₂ peaked at the time of embolectomy and then decreased,and peaked again during estrus.4.Estrus induction and reproduction test of early weaning ewes in autumn and winter lambing.According to the results of the spring estrus induction experiment,PMSG was used as an auxiliary treatment,which was divided into 0 d CIDR+PMSG+PG and-7 d CIDR+PMSG+PG.The estrus rate of the two treatment schemes was more than 70.00%.The pregnancy rate was 81.16%and 86.54%,respectively,according to the results of B-ultrasound diagnosis within 60 days after mating.The above experiments show that:（1）The natural estrus of Tan sheep ewe in the early postpartum period has obvious seasonality,The monitoring results of reproductive hormones in ewe’s peripheral blood reveal the recovery time of ewe’s ovarian activity in different seasons after delivery,It provides a physiological basis for further exploring the treatment scheme of estrus induction for early weaned ewes in different seasons.（2）In the treatment scheme of estrus synchronization,progesterone preparation or prostaglandin was used as the main treatment scheme,which achieved good estrus effect;Both schemes can be assisted by PMSG 500 produced by Ningbo Second Hormone Factory to obtain higher pregnancy rate.The results of reproductive hormone monitoring provide theoretical basis for exploring the relationship between the change of reproductive hormone content in peripheral blood and estrus time and screening the best artificial insemination time.（3）In order to further realize the intensive reproduction of three times lambing in two years,nduction of estrus in different seasons for early weaning ewes could be started after early weaning,and induction of estrus with progesterone and PMSG could be started 7 days before weaning.