Study On The Regulatory Mechanism Of Anti-heat Stress Characteristics Of Turpan Black Sheep On The Reproductive Performance Of Ewes

The ancestors of sheep were initially domesticated from the Free Asian Mouflflon sheep,But different sheep populations show obvious differences in growth and production traits in order to adapt to different geographic regions.Turpan region is known for its unique hot climate as"fire zone",its average summer temperature is more than 35℃,more than 42℃at the hottest at noon,this extreme high temperature environment would lead to physio logical,biochemical and hormonal alterations,which have a negative impact on immunity,growth,reproduction and produc tion performance in sheep.The unique local sheep kind of Turpan black sheep evolved with great adaptability in high temperature in Turpan Basin,But the mechanism is not yet known.So this study in turpan black sheep as the study object,further study the hormone changes,heat stress reproductive characteristics and molecular and physiological mechanism of heat stress,to fill the gap in the field,mining its variety advantage,and to provide a theoretical basis for the reproductive performance of Turpan black sheep,to improve the reproductive rate of hot areas in sheep,and provide genetic evaluation for the selection of heat resistant varieties.Furthermore In-depth research in local sheep breeds is not only important for germplasm resources protection but also for designing sheep breeding program.The main contents of the research are as follow:（1）The dynamics of reproductive and metabolism hormones in the plasma of Turpan Black Sheep during estrus cycle Turpan Black Sheep were randomly selected to conduct estrus with ram in the morning and evening with recording the time interval and duration of the estrus cycle.The average interval of estrus is 15.76 d and the average estrus duration is 32.25 h.Furthermore,the level of reproductive hormones and metabolism hormones in plasma,including follicle-stimulating hormone（FSH）,luteinizing hormone（LH）,estradiol（E₂）,progesterone（P₄）,triiodothyronine（T3）,growth hormone（GH）and corticotropin releasing hormone（CRH）,were detected in the proestrus,estrus,metaestrus and dioestrus.LH and FSH show pulse-like changes while P₄and E₂show volatility changes during the estrus cycle.The secretion of T3,GH and CRH fluctuated throughout the estrus cycle.But concentration of LH and P₄fluctuated on a higher lever promoted by CRH during the dioestrus.For the first time,this study reported that the average interval,reproductive hormones and other related hormones secretion of estrus cycle about Turpan Black Sheep,which provide valuable information to study the heat resistant trait and behind mechanisms among desert area ruminant.（2）The purpose of this experiment was to study the changes of serum reproductive hormones in Turpan black sheep in four seasons,In this study,ELISA was used to determine serum follicle-stimulating hormone（FSH）,luteinizing hormone（LH）,estrogen（E₂）and progesterone（P₄）in spring,summer,autumn and winter respectively.The results showed that the content of FSH,LH,E₂and P₄in the blood of Turpan black sheep showed significant seasonal changes.The content of FSH,LH and E₂in summer and autumn were significantly higher than those in spring and winter,and the content of P4 was significantly higher in spring and winter than in summer and autumn;the rising and falling trends of the four hormones during estrus were consistent,and there was no obvious seasonal differences,and Turpan black sheep can naturally estrus in different seasons,and the best natural estrus effect is summer and autumn.（3）Identifying the heat resistant genes by multi-tissue transcriptome sequencing analysis in Turpan Black sheep.In this study,85 Turpan Black sheep,a breed exhibited excellent heat resistance from longterm artifificial selection,and 85 heat sensitive Kazakh sheep in Turpan basin were tested for physiological and reproductive performance from July to August in summer.The results showed that the estrus rate and conception rate was signifificantly higher in Turpan Black sheep（P<0.05）,while the heart rate and respiratory rate of Turpan Black sheep are signifificantly lower than that of Kazakh sheep（P<0.05）.Furthermore,to clarify genes participated in heat stress response,the pituitary,ovarian and hepatic tissues from three Turpan Black sheep and three Kazakh sheep were subjected to RNA-seq.The results indicated that 32,49 and 69 genes were up-regulated,and 39,60 and 145 genes were down-regulated in pituitary,ovarian and hepatic tissues in Turpan Black sheep compared with that of the Kazakh sheep,respectively.KEGG and gene set enrichment analysis showed that the differentially expressed genes were mainly involved in signal transduction pathways.In particular,the differentially expressed genes in hepar were enriched in the energy metabolism pathway,while the differentially expressed genes in ovarian tissue were enriched in the ovarium steroidogenesis pathway.In conclusion,our results implied that the pituitary-ovary axis might include hepar as downstream targeted organism in heat resistant regulation.Under heat stress,the signals released from pituitary would impact steroidogenesis in ovary,and further alter energy metabolism in hepar.As we know,this is the fifirst comparative study to investigate the gene expression in multi-tissue in sheep under heat stress.