Dynamics In Rumen And Distribution Along Gastrointestinal Tracts Of Bacteria And Methanogen In Yak

For a long co-evolution time, seasonal imbalance of biomass production and the harsh environment in Qinghai-Tibetan Plateau has resulted in a series of unique adaptation mechanisms for yak to withstand cold, low oxygen, high UV radiation, nutritional deficiencies. The microflora in rumen is an important nutrition reservoir to support host to resist external stress. Revealing dynamics in rumen and distribution along the gastrointestinal tracts of bacteria and methanogen would help to clarify the essential characteristics of "nitrogen and carbon salvage" of grazing yaks. Based on our previous work, this study mainly focused on the colonization of rumen microflora(bacteria and methanogen) under different growing stages of grazing yak, seasonal variation of rumen microflora of adult yak and distribution of bacteria and methanogen along the gastrointestinal tracts of yak. The study was carried out by highthroughput sequencing(Miseq), prediction analysis(PICRUSt) and other biotechnology. The identification of unique gut microflora related to the harsh environment adaptation could provide theoretical and technical support to the sustainable development of Tibetan ecological livestock husbandry. The main result of this study as follows:1. The Chao1 of the rumen bacteria and methanogen along different ages was stage 1(3 and 14 day)<stage 2(60, 180 and 365 day)<730 day. The Shannon index was the lowest at stage 1 without difference between other age groups.2. The dominant bacteria phylum ignoring different ages were Firmicutes, Bacteroidetes and Proteobacteria, accounting for 85%. The highest relative abundance was Firmicutes, which was stable at 50% under different ages. The relative abundance of Bacteroidetes increased from 23% at 3 day to 43% at 730 day. In contrast, The relative abundance of Proteobacteria decreased from 17% at 3 day to 2.3% at 730 day. However the changes could be divided into three stages: stage 1(3, 14 day), stage 2(60, 180 day) and stage 3(365, 730 day).3. The oral microflora of mother was the main source for the establishment of the rumen in young animals.4. The relative abundance of methanogen increased from 0.3% at 3 day to the highest value of 2% at 60 day and then kept at 1.3% at stage 3.5. The order of diversity of rumen bacteria and methanogen under different seasons was Spring>Sumer>Winter. The similarity within group was Spring <Winter<Summer.6. The dominant phylum of bacteria were Firmicutes and Bacteroidetes, which were 75%, 80% and 77% at Spring, Summer and Winter, respectively. The relative abundance of Bacteroidetes was highest at Spring about 45% and at same level with 54% at Summer and Winter. The Firmicutes was 30, 26 and 23% at Spring, Summer and Winter, respectively.7. At cold season(Spring and Winter), due to the forage contains high content of fibre, the abundance of fibre degradation genus was higher than warm season(Summer). While the genus of secondary metabolites decomposer was higher at Summer. Methanogen was lowest at Winter. The changes of microbe in rumen of yak was driven by the compositions of the grass and temperature.8. Under the same diet, no difference of alpha and beta diversity were found between yak and cattle. The order of the Chao1 and Shannon values was forestomach content and large intestine>forestomach tissue>small intestine. The similarity within group was lowest in small intestine. The NSTI index from PIRUSt was higher in yak compare with cattle, suggested that the more unclassified bacteria and methanogen existed in the gut of yak.9. The dominant phylum of bacteria were Firmicutes and Bacteroidetes, which were 75% in forestomach and small intestine, 90% at large intestine. The relative abundance of Firmicutes was higher in small and large intestine than that in forestomach. In contrast, Bacteroidetes was higher in forestomach than that in small and large intestine. The Cyanobacteria phylum was higher in the gut of yak compare with cattle.10. The distribution of microflora along the longitudinal axis of the intestines was driven by the function and physical environment of gut. The forestomach tissue was mainly involved in the metabolism of oxygen, urea and volatile fatty acid. Digestion of the fibre, starch, sugar and secondary metabolites of forage was the dominant function in forestomach. Some genus involved in vitamin production and mucin degradation was higher in small intestine, and involved in sugar, salt and toxin compounds metabolism was dominant in large intestine.This study focused on the dynamics in rumen and distribution along gastrointestinal tracts of bacteria and methanogen in yak. And we used PICRUSt to predict the function of bacteria and methanogen, which provided theoretical and technical support to the sustainable development of Tibetan ecological livestock husbandry.