Abstract
Strategies to manage metabolic hydrogen ([H]) in the rumen should be considered when reducing ruminant methane (CH4) emissions. However, little is known about the use of dietary treatments to stimulate rumen microorganisms capable of capturing the [H] available when CH4 is inhibited in vivo. The effects of the phenolic compound phloroglucinol on CH4 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 were randomly allocated in two groups receiving chloroform as an antimethanogenic compound for 21 days. Following that period one group received chloroform + phloroglucinol for another 16 days, whilst the other group received only chloroform during the same period. The chloroform treatment resulted in a decrease in CH4 production and an increase in H2 expelled with a shift in rumen fermentation toward higher levels of propionate and formate and lower levels of acetate at day 21 of treatment. Bacterial operational taxonomic units (OTUs) assigned to Prevotella were promoted whilst Archaea and Synergistetes OTUs were decreased with the chloroform treatment as expected. The shift toward formate coincided with increases in Ruminococcus flavefaciens, Butyrivibrio fibrisolvens, and Methanobrevibacter ruminantium species. The addition of chloroform + phloroglucinol in the rumen resulted in a decrease of H2 expelled (g) per kg of DMI and moles of H2 expelled per mol of CH4 decreased compared with the chloroform only treated animals. A shift toward acetate and a decrease in formate were observed for the chloroform + phloroglucinol-treated animals at day 37. These changes in the rumen fermentation profile were accompanied by a relative increase of OTUs assigned to Coprococcus spp., which could suggest this 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 decreased by redirecting [H] toward alternative sinks through the nutritional stimulation of specific microbial groups. This results in the generation of metabolites of value for the host while also helping to maintain a low H2 partial pressure in the methane-inhibited rumen.
Highlights
Methane is a potent greenhouse gas and represents a loss of gross feed energy for the ruminant, the increasing interest in strategies to manipulate CH4 production (Johnson and Johnson, 1995; Gerber et al, 2013)
No significant effects were observed on DMI, average daily weight gain, CH4 and H2 production (g/kg DMI), and fermentation parameters between experimental groups at either the control period or at day 21 of chloroform treatment before supplementation with phloroglucinol (Supplementary Tables 1, 2)
A significant decrease (P ≤ 0.05) in CH4 production (g/kg DMI) (40% reduction) and increase in H2 (1.2 H2 g/kg DMI) were observed in both groups of animals treated with chloroform compared with their respective control period
Summary
Methane is a potent greenhouse gas and represents a loss of gross feed energy for the ruminant, the increasing interest in strategies to manipulate CH4 production (Johnson and Johnson, 1995; Gerber et al, 2013). Archaea produce CH4 in the rumen mainly by reducing C1 compounds with H2 (among others substrates) maintaining a low hydrogen partial pressure (Janssen, 2010). Methanogens are the main H2 consumers, due to the thermodynamically favorable pathway of CH4 formation, there are rumen bacteria, which are able to use H2 as substrate generating alternative end products (Leng, 2014). An excessive increase of the H2 partial pressure in the rumen after methane inhibition might have detrimental effects on rumen function (Wolin et al, 1997). Management of H2 accumulation in the rumen is an important strategy to consider when inhibiting CH4 emissions from livestock
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