Effect Of Slow-release Urea On The Composition Of Ruminal Bacteria And Fungi Communities In Yak

Yak is typical ruminant animals living in the Qinghai-Tibetan Plateau.Yak has evolved a high nitrogen utilization rate in the harsh environment with cold,low oxygen and seasonal imbalance of biomass production after a long adaptation.Previous studies demonstrated that the rumen microbiota of yak not only significantly differs different from the other ruminants,but also played an important role in the metabolism and utilization of nitrogen.Therefore,examining the relationship between rumen microorganisms and nitrogen metabolism will improve our understanding of about the yak adaptation.Slow-release urea(SRU)is a non-protein nitrogen that can be hydrolyzed to ammonia by rumen microbiota.SRU can be a good model for studying rumen nitrogen metabolism of yak.However,the effect of slow-release urea on the composition and function of the rumen of yak remains unclear.We arranged two dietary treatments: a basal diet containing 10 or 20 g/kg diet of SRU(designated LSRU and HSRU,respectively)to investigate the effect of slow-release urea on the composition and function of the rumen microorganisms of yak.The results showed the average daily weight gain and feed efficiency for yaks fed the LSRU diet were better than for those fed the HSRU diet.The dominant bacterial genera were Prevotella 1,Rikenellaceae RC9 gut group,and Christensenellaceae R-7 group(accounting for 38.7,8.73 and 2.51% of detected OTUs,respectively).Increasing SRU supply significantly decreased(P < 0.05)abundance of the phylum Chlorobi and genus Rikenellaceae RC9 gut group.The dominant fungal genera were Saccharomycopsis,Candida,and Pseudopithomyces(accounting for 22.44,5.26 and 3.32% of detected OTUs,respectively).Increasing SRU supply significantly decreased(P < 0.05)abundance of Pichia,Geotrichum and Monographella genera.Furthermore,the predicted functions of D-glutamine and D-glutamate metabolism were significantly decreased(P < 0.05)with an increase in SRU.Our results suggest that SRU has influenced rumen microbiota of yaks,and identified key microorganisms and metabolic pathways associated with urea metabolism,which provides new insights in understanding the urea metabolism,and shed lights on the urea application of yaks and other ruminants lived at Qinghai-Tibetan Plateau.