Effect Of Rumen Fermentation-host-microbe Interaction On The Adaptation To Cold Environment Of Grazing Tibetan Sheep

Tibetan sheep is the oldest primitive sheep breed on the Qinghai-Tibet Plateau,and it’s one of the three major coarse wool sheep breeds in China.It plays an important role in genetic resource and dominant livestock species of Qinghai-Tibet Plateau.In the condition of high cold,low oxygen,and nutrient deficiencies,it lives normally and has reproduction ability,which is related to their special plateau adaptability.In order to analyze the adaptability of Tibetan sheep to the plateau ecological limiting factors,and to explore their special mechanisms for adapting to the cold plateau environment.In this study,rumen fermentation function,rumen epithelial tissue structure and expression characteristics,and microbial community structure of grazing Tibetan sheep（1 years old,♀）in cold and warm seasons were compared and analyzed,with a view to multi-angle and multi-level systemic exploration of the cold-season Tibetan sheep’s plateau cold adaptation mechanism.The main results of this study are as follows:1.There were significant differences in volatile fatty acids（VFAs）of Tibetan sheep rumen fluid in cold and warm seasons that the content of total VFAs in the cold season was significantly higher than those of in the warm season（P<0.01）,including Acetate,Propionate and Butyrate in the cold season showed significantly higher than those of in the warm season（P<0.05）.In the cold season,the expression of gene DRA and MCT-1 related to the transport of VFAs were up-regulated while the expression of gene AE2 and NHE2 were down-regulated.In addition,the rumen liquid ammonia nitrogen content（NH₃-N）of cold-season Tibetan sheep decreased,and cellulase（CL）activity increased.2.The development of rumen epithelial tissue in grazing Tibetan sheep was affected by nutritional stress in the cold season.The width of the rumen muscle layer and papilla and the thickness of the stratum corneum,granular layer and spinous layer of the rumen epithelial layer showed that were significant increase in the cold season（P<0.05）,and the stratum corneum partly shed.Furthermore,the expression of gene SGLT1,Claudin-4 and ZO-1 that respectively related to nutrient absorption and barriers in rumen epithelial tissues were down-regulated in the cold season.3.There were significant differences in rumen microflora in cold and warm seasons,and the abundance of microbial species in the cold season was significantly higher than that of in the warm season（P<0.05）.The abundance of Bacteroidetes increased significantly（P<0.05）and the abundance of Firmicutes decreased significantly at the Phylum level in the cold season（P<0.05）.The abundance of Prevotella＿1 and Succiniclasticum about the production of Propionate decreased and the abundance of Ruminococcus 2 about fiber degradation,significantly increased（P<0.05）,and the energy metabolism significantly increased at the Genus level in the cold season（P<0.05）.4.The host genes were related to rumen epithelial morphology.The SGLT1 gene about nutrient absorption was significantly positively correlated with papillary height（P<0.05）,and was significantly negatively correlated with granular layer thickness and spinous layer thickness（P<0.05）.The DRA gene about VFAs transport was significantly negatively correlated with nipple height（P<0.05）,and NHE2 gene was significantly negatively correlated with spinous layer thickness.In addition,the bacterial flora about cellulose degradation in the rumen also was related to VFAs,including which Pseudobutyrivibrio,Ruminococcaceae-NK4A214-group,Butyrivibrio-2 were significantly correlated with VFAs（P<0.05）,and microbe-VFAs-host genes,Christensenellaceae-R-7-group,Rikenellaceae-RC9-gut-group were significantly positively correlated with Acetate,Propionate,Butyrateand Valerate,and likewise with DRA gene（P<0.05）.In summary,this study comprehensively analyzed the characteristics of rumen environmental changes of grazing Tibetan sheep in cold and warm seasons.Nutritional stress leaded to enhanced rumen fermentation function and adaptive changed in rumen epithelial morphology and host gene expression of grazing Tibetan sheep in cold season,as well as the structure of the rumen microbial flora changed.Taken together,these results about adaptive changes revealed the correlation between rumen fermentation-host-microorganism,suggesting that the VFAs produced by rumen microbes were controlled and absorbed by rumen epithelial tissue structure and a related gene,which revealed the special adaptability of Tibetan sheep in the cold season,and provided a certain basis for future research on the adaptability of grazing Tibetan sheep in the cold season.