Effect of slow-release urea on the composition of ruminal bacteria and fungi communities in yak

Abstract

Slow-release urea (SRU) is a cost-efficient form of nonprotein nitrogen, which is hydrolyzed and synthesized by rumen microorganisms, and affects ruminant production performance. Yaks have evolved efficient microbial protein synthesis on the Qinghai-Tibetan Plateau (QTP). Examining effects of SRU on rumen microbiota is important to understand the urea metabolism in rumen of yak, however, which has not been previously characterized. To this end, six healthy yaks were selected and randomly assigned to one of two dietary treatments: a basal diet containing 10 or 20 g/kg diet of SRU (designated LSRU and HSRU, respectively, n = 3 in each case). Rumen bacteria and fungi community based on 16S rRNA and ITS1 genes, respectively, were characterized through the next-generation sequencing. 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. Overall, these results suggest that SRU has influenced rumen microbiota of yaks, which provides new insights in understanding the urea metabolism, and shed lights on the urea application of yaks and other ruminants lived at QTP.