Heat Stress Induces Shifts in the Rumen Bacteria and Metabolome of Buffalo

SIMPLE SUMMARY: Heat stress is a major factor in causing substantial losses to the livestock industry, due to its negative effects on milk production, fertility, health and welfare. As the second largest diary producing species, buffalo face challenges from heat stress. To explore the nutritional metabolic mechanism of rumen bacteria in buffalo under hot enviroments, this study used 16S rDNA technology and metabolome analysis to identify heat stress-related bacteria, metabolites and their pathways. Our findings showed that heat stress increased respiratory rate and skin temperature, and decreased rumen volatile fatty acids. The structures of rumen bacterial communities at different levels significantly changed and a total of 32 metabolites mainly involved in gluconeogenesis were altered due to heat stress. Overall, this study improves our understanding of ruminal bacterial and metabolic alterations of buffalo exposed to heat stress. ABSTRACT: Exposure to the stress (HS) negatively affects physiology, performance, reproduction and welfare of buffalo. However, the mechanisms by which HS negatively affects rumen bacteria and its associated metabolism in buffalo are not well known yet. This study aimed to gain insight into the adaption of bacteria and the complexity of the metabolome in the rumen of six buffalo during HS using 16S rDNA and gas chromatography metabolomics analyses. HS increased respiratory rate (p < 0.05) and skin temperature (p < 0.01), and it decreased the content of acetic acid (p < 0.05) and butyric acid (p < 0.05) in the rumen. Omics sequencing revealed that the relative abundances of Lachnospirales, Lachnospiraceae, Lachnospiraceae_NK3A20_group and Clostridia_UCG-014 were significantly (p < 0.01) higher under HS than non-heat stress conditions. Several bacteria at different levels, such as Lactobacillales, Streptococcus, Leuconostocaceae and Leissella, were significantly (p < 0.05) more abundant in the rumen of the non-heat stress than HS condition. Thirty-two significantly different metabolites closely related to HS were identified (p < 0.05). Metabolic pathway analysis revealed four key pathways: D-Alanine metabolism; Lysine degradation, Tropane; piperidine and pyridine alkaloid biosynthesis; and Galactose metabolism. In summary, HS may negatively affected rumen fermentation efficiency and changed the composition of rumen community and metabolic function.