Phloroglucinol degradation in the rumen promotes the redirection of hydrogen when methanogenesis is suppressed

Strategies to manage metabolic hydrogen ([H]) in the rumen should be considered when reducing ruminant methane emissions. However, little is known about the use of dietary treatments to stimulate rumen microorganisms capable of capturing the [H] available when methane is inhibited in vivo. The effects of a phenolic compound (phloroglucinol) on methane production, [H] flows and subsequent responses in rumen fermentation and microbial community composition when methanogenesis is inhibited were investigated in cattle. Eight rumen fistulated Brahman steers fed ad libitum with a ratio 60:40 forage:concentrate were randomly allocated in two groups receiving chloroform as antimethanogenic compound for 21 days. Following that period one group received the chloroform + phloroglucinol, whilst the other group just received the chloroform for 16 days. The chloroform treatment resulted in an increase in H2 expelled as methane production decreased with a shift in rumen fermentation towards propionate and formate at day 21 of treatment. Also OTUs assigned to Prevotella were promoted whilst archaea OTUs were decreased with the chloroform treatment as expected. The addition of phloroglucinol in the rumen resulted in a decrease of H2 expelled (g) per kg of DMI and moles of H2 expelled per mol of methane decrease compared with the chloroform only-treated animals. A shift towards acetate and a decrease in formate were observed on the phloroglucinol-treated animals. These changes in the rumen fermentation were accompanied by an increase of OTUs assigned to Coprococcus spp., which could suggest the genus is a significant contributor to the metabolism of this phenolic compound in the rumen. This study demonstrates for the first time in vivo that under methanogenesis inhibition, H2 gas accumulation can be reduced by redirecting [H] towards alternative sinks through the nutritional stimulation of microbial groups that generates metabolites of value to the host and also it might help to decrease the partial pressure of H2 in the methane-inhibited rumen.