The Development Model Of Microbiota In The Rumen Of Grazing Yak

With the long-term natural selection and artificial domestication,yak has evolved much unique adaptation mechanism to fight against the harsh environment in the Qinghai-Tibetan Plateau such as cold,low level oxygen,strong UV radiation and shortage of nutrition.The rumen microbiome fermentation ecosystem is an important nutritional reservoir to support survival and production of the host.Elucidation of rumen microbial composition structure and function will play a crucial role in improving the yak productive performance.Based on previous studies,the genes associated with highaltitude adaptation were enriched in the yak compared to cattle,the genes that negatively affected the high-altitude adaptation were down-regulated in yak,and it posed unique ruminal methanogens compared to cattle.In addition,the rumen microbiome of yak was characterized by low methane emission and high volatile fatty acids production compared to cattle via metagenomic and metatranscriptomic technique.Thus,we speculated that the microbiota in the rumen of yak might have special development model in order to help the host adapt to the harsh environment in the QinghaiTibetan Plateau.This study was conducted to profile the source and colonization process of rumen microbiota,and to elucidate the microbial mechanism of yak that endured forage feeding via comparing rumen microbial composition and function to cattle at different seasons,which will modulate the rumen fermentation to improve yak productivity and provide basic information on realizing the sustainable development of livestock husbandry in the Qnghai-Tibetan Plateau.The main results were listed as follows:1.From 7 days to month 6,the rumen microbiota from female yak contributed the most to the source of calves’ rumen microbiota,followed by saliva,milk and skin breast.The contribution value of microbiota from different types of sample(rumen,saliva,milk and teat skin)fluctuated remarkably at different growth stages.2.The bacteria were detected in the rumen at day 7,followed by archaea(day 14),fungi and protozoa were detected at day 30.The richness of rumen microbiota increased from day 7 to 2 years old and then remained stable.The bacterial and archaeal community were affected by age,while fungal and protozoal community were less sensitive to age.3.The dominant bacterial taxa were Prevotella 1(13.1%)and Rikenellaceae RC9 gut group(10.8%),Methanobrevibacter ruminantium clade(37.8%)and Methanobrevibacter gottschalkii clade(34.8%)were the dominant archaeal taxa,Caecomyces(35.3%)and Orpinomyces(29.1%)were the dominant fungal taxa,Entodinium(19.2%)and Dasytricha(17.2%)were the dominant protozoal taxa.4.The maturation of rumen microbiota was different from each other,for example,archaea matured at about 5 years old,bacteria,fungi and protozoa matured between 5 and 8 years old.Christensenellaceae R-7 group,Prevotella 1,Trichostomatia,Ruminococcaceae UCG-014 and Lachnospiraceae were the keystone species during the rumen development period.5.The microbial composition and function(bacteria and archaea)in the rumen of yak and cattle were affected by both season and host.The bacterial diversity in the rumen of yak and cattle significantly decreased with season,while that in archaea vairied across seasons.6.The relative abundance of some functional taxa showed seasonal change,for example,the relative abundance of Fibrobacter succinogenes(fiber degradation)increased significantly with season,whereas the relative abundance of Selenomonas ruminantium(starch fermentation)decreased significantly with season.The abundance of pathways linked to carbohydrate increased from summer to winter in the rumen of yak,and the abundance of CAZymes(fiber degradation)and enzyme activity(celluase)were higher in yak compared to cattle.The diversity of antimicrobial genes in the rumen of cattle was higher than in yak,and the dominant antibiotic classes in the rumen were Rifamycin,Tetracycline,Peptide,Lincosamidea and Beta-lactamas.7.The rumen microbiome stability fluctuated greatly with season,the stability in yak was numerically higher than in cattle,especially in winter.Some antimicrobial genes and CAZymes families showed positive associations with rumen microbiome stability,and these associations were host-specific.The present study first comprehensively revealed the source and colonization of rumen microbiota,and the seasonal response of rumen microbiome in grazing yak was also elucidated via metagenomic sequencing technique,which provided solid theoretical basic information to reveal how the yak adapts to harsh environment and nutritional stress in the Qinghai-Tibetan Plateau.