Microbial Succession In Gastrointestinal Tract And Driving Factors Of Their Adaptation To Alpine Stress In Yak

Yaks live in a special geographical environment of the Qinghai-Tibet Plateau all the year-round.They developed a unique rumen microecosystem after long-term natural selection and evolution,which plays an important role in the co-evolution process of coping with the adversity of the plateau.At present,the research on the gastrointestinal microbial succession and driving factors in the adaption of grazing yak to the cold and harsh ecological environment is still very limited.The purpose of this study was to study the origin,colonization,and succession of ruminal and intestinal microbial communities of yak and cattle calves at different developmental stages residing in the same habitat.Moreover,the seasonal dynamics and driving factors of rumen anaerobic fungal community in yaks and cattle under cold stress were also studied to reveal the changes in the rumen microbial structure and function of yak and its response mechanism to cold stress,and to provide the theoretical basis for breeding and environmental adaptation of characteristic breeds under extreme environment.The main results are as follows:1.The predominant intestinal microbiota in yak and cattle calves during different developmental stages were mainly Ruminococcaceae,Bacteroidaceae,and Lachnospirnoaceae.Source Tracker analysis revealed that the maternal fecal microbial community was critical for rapid colonization of the intestinal microbial community in early developing calves(average contribution was about 90%).In comparison to cattle calves,the intestinal microbial community of yak calves was relatively stable at 5 ～9 weeks after birth(Wilcoxon test,P > 0.05).At the same time,there was no significant difference in Shannon diversity index and Chao1 species richness index of intestinal microbiota in yak calves during different months after weaning as compared to cattle calves(Kruskal-Wallis test,P > 0.05).In addition,the structure of intestinal microbiota of yak and cattle calves became similar gradually with the increase in calf age.2.The dominant rumen microflora of yak and cattle calves at different developmental stages were mainly composed of Ruminococcaceae,Prevotellaceae,Rikenellaceae,and Lachnospiraceae.There was no significant difference in rumen microbial community structure and diversity between yak and cattle calves from birth to weaning.At the same time,LEf Se analysis found significant age discriminating rumen microbial composition and their relative abundances between yak and cattle calves at different developmental stages.3.Based on the latest UNITE database and NCBI database,12 anaerobic fungal(AF)genera were annotated in the rumen of yak and cattle during different grazing months,of which Caecomyces,Cyllamyces,and Orpinomyces were dominant genera.The structure of the rumen AF community during different grazing months showed dynamic changes and significant differences(Kruskal-Wallis test,P <0.001).The species richness of the rumen AF community in the cold season was significantly higher compared to the warm season(Wilcoxon test,P < 0.05).Random Forest analysis showed that Feramyces,Tahromyces,and Buwchfawermyces were important seasonal indicators in the rumen of yak,while Caecomyces,Cyllamyces,and Piromyces were important indicators in the rumen of cattle.The analysis of the null model showed that the seasonal dynamics of rumen AF community structure was mainly influenced by certain factors,and was significantly correlated with climatic factors,forage nutrition,and rumen volatile fatty acids.Mantel test and structural equation model showed that forage fiber was an important driving factor for the seasonal dynamics of rumen AF community structure in grazing livestock.To sum up,the succession rule and driving factors of rumen and intestinal microbial communities of yaks and cattle at different developmental stages under natural grazing conditions were studied,it will be helpful to make a reasonable control strategy to improve the structure of gastrointestinal microbiota of grazing livestock and improve its production performance.