Effect of Heat Stress on Rumen Microbial Diversity and Fermentation Pattern in Buffalo

Abstract

In this study, changes in rumen microbiome and fermentation were examined during heat stress (HS) in buffaloes. Six buffalo heifers were exposed to thermoneutral ( $\text{THI}=72$ ) and HS ( $\text{THI}=87–90$ ) conditions for 6 h between 10 AM and 4 PM for 21 days in the climatic chamber. A digestibility trial with four-day collection period was conducted at the end of the study, and rumen liquor was collected on day 21. At the phylum level, an increased ( $p<0.05$ ) abundance of Firmicutes and a decreased ( $p<0.05$ ) abundance of Proteobacteria and Planctomycetes were observed during HS compared to thermoneutral conditions. The abundance of 6 different genera of phylum Firmicutes, YRC22 (phylum Bacteroidetes), and Stenotrophomonas (phylum Proteobacteria) was increased ( $p<0.05$ ), whereas B. firmus, Lysinibacillus, Bacteroides unclassified genus (family Enterobacteriaceae), and Methanobrevibacter decreased ( $p<0.05$ ) during HS compared to control. Eight new genera from four different phyla were detected after HS exposure, whereas one genus was not detected in the rumen after HS exposure, which was present during thermoneutral conditions. Dry matter intake, volatile fatty acid concentration, and digestibility did not change ( $p>0.05$ ) during HS. It can be concluded that the resilience of the rumen microbial population invokes adaptive responses by changing their abundance to minimize the adverse effects on fermentation and digestibility in buffalo heifers.