Effect of rumen microbiota transfaunation on the growth, rumen fermentation, and microbial community of early separated Japanese Black cattle

This study aimed to investigate the effect of rumen microbiota transfaunation on the growth, rumen fermentation, and the microbial community of Japanese Black cattle that were separated early from their dams. Here, 24 calves were separated from their dams immediately after calving, 12 of which were transfaunated via inoculation with rumen fluid from adult cattle at the age of 2 months while the remaining 12 were kept unfaunated (not-inoculated). Feed efficiency monitoring was performed during 7-10 months of age. Body weight and feed intake were not significantly different between the transfaunated and unfaunated cattle. Transfaunation increased the relative levels of acetate and butyrate but decreased those of propionate, which increased the non-glucogenic/glucogenic short-chain fatty acid ratio. Microbial 16S, 18S, and ITS ribosomal RNA gene amplicon analysis showed that rumen microbial diversity and composition differed between transfaunated and unfaunated cattle; transfaunation increased the abundance of acetate- and butyrate-producing bacteria, and decreased the abundance of bacterial genera associated with propionate production. Transfaunation also increased the abundance of Methanomassiliicoccaceae_group10 (1.94% vs. 0.05%) and Neocallimastix (27.1% vs. 6.8%) but decreased that of Methanomicrobium (<0.01% vs. 0.06%). Our findings indicate that rumen microbiota transfaunation shifts rumen fermentation toward acetate and butyrate production through a change in the rumen microbial composition in Japanese Black cattle.