Methane Inhibition Alters the Microbial Community, Hydrogen Flow, and Fermentation Response in the Rumen of Cattle

Abstract

Management of metabolic hydrogen ([H]) in the rumen has been identified as an important consideration when reducing ruminant CH4 emissions. However, little is known about hydrogen flux and microbial rumen population responses to CH4 inhibition when animals are fed with slowly degradable diets. The effects of the anti-methanogenic compound, chloroform, on rumen fermentation, microbial ecology, and H2/CH4 production were investigated in vivo. Eight rumen fistulated Brahman steers were fed a roughage hay diet (Rhode grass hay) or roughage hay:concentrate diet (60:40) with increasing levels (low, mid, and high) of chloroform in a cyclodextrin matrix. The increasing levels of chloroform resulted in an increase in H2 expelled as CH4 production decreased with no effect on dry matter intakes. The amount of expelled H2 per mole of decreased methane, was lower for the hay diet suggesting a more efficient redirection of hydrogen into other microbial products compared with hay:concentrate diet. A shift in rumen fermentation toward propionate and branched-chain fatty acids was observed for both diets. Animals fed with the hay:concentrate diet had both higher formate concentration and H2 expelled than those fed only roughage hay. Metabolomic analyses revealed an increase in the concentration of amino acids, organic, and nucleic acids in the fluid phase for both diets when methanogenesis was inhibited. These changes in the rumen metabolism were accompanied by a shift in the microbiota with an increase in Bacteroidetes:Firmicutes ratio and a decrease in Archaea and Synergistetes for both diets. Within the Bacteroidetes family, some OTUs assigned to Prevotella were promoted under chloroform treatment. These bacteria may be partly responsible for the increase in amino acids and propionate in the rumen. No significant changes were observed for abundance of fibrolytic bacteria, protozoa, and fungi, which suggests that fiber degradation was not impaired. The observed 30% decrease in methanogenesis did not adversely affect rumen metabolism and the rumen microbiota was able to adapt and redirect [H] into other microbial end-products for both diets. However, it is also required dietary supplements or microbial treatments to capture the additional H2 expelled by the animal to further improve rumen digestive efficiency.

Rumen microbial responses to supplemental nitrate. II. Potential interactions with live yeast culture on the prokaryotic community and methanogenesis in continuous culture

“…Live yeast tended to increase (P = 0.07) acetate: propionate by increasing (P = 0.05) acetate and numerically (P = 0.13) decreasing propionate. Isobutyrate and valerate were also decreased (P < 0.01) by NO 3 − , potentially resulting from a disruption of branched-chain AA deamination, although responses are mixed and probably depend on various factors (Martinez-Fernandez et al, 2016). Desnoyers et al (2009) reported no effect on acetate: propionate ratio in vivo in a meta-analysis of S. cerevisiae studies.…”

Metabolic Hydrogen Flows in Rumen Fermentation: Principles and Possibilities of Interventions

“…It is thus possible that, the same as H 2 , formate concentration has an influence on CH 4 production and the VFA profile. Other than an accumulation of formate as a response to methanogenesis inhibitors in some studies (Ungerfeld et al, 2003;Martinez-Fernandez et al, 2016, 2017, the effects of variables such as outflow rates, pH, or rate of fermentation on formate concentration, have not been investigated to the author's knowledge. Generating information about the relationship between those variables and formate concentration, and how they relate to methanogens growth rate would be important for evaluating the influence of formate on the VFA profile, and integrating formate to a model of [H] flows in rumen fermentation.…”

“…Lactate is another intercellular e − carrier which, except for lactic acidosis, normally does not accumulate in the rumen and is extensively converted to VFA by various lactate utilizers (Chen et al, 2019). Small amounts of lactate have been reported to accumulate as a consequence of inhibiting methanogenesis in some (Amgarten et al, 1981), but not all (Božic et al, 2009;Martinez-Fernandez et al, 2016), studies. In general, lactate accumulation in the rumen is the result of lactate production rate surpassing lactate utilization as a consequence of rapid fermentation.…”

“…Pathways of [H] flow alternative to H 2 formation can result in the production of other intercellular e − carriers, such as lactate, ethanol, and formate, or final fermentation products such as propionate, all of which also help NADH oxidation (Van Lingen et al, 2016). Formate, succinate or ethanol have been shown to accumulate along with H 2 when methanogenesis was inhibited in vitro (Slyter, 1979;Asanuma et al, 1998;Ungerfeld et al, 2003) and in vivo (Martinez-Fernandez et al, 2016, 2017Melgar et al, 2019), so it is important to understand if the accumulation of those metabolites could potentially inhibit cofactors re-oxidation and fermentation. The effects of lactate, ethanol, formate and propionate on fermentation and digestion are best studied in experiments in which those metabolites are externally added to rumen fermentation as pure compounds.…”

Physiological and rumen microbial responses of Angus cattle (Bos taurus) following exposure to heat load

“…The tubes were incubated at 70 ⁰C for 15 min before being centrifuged at 14000 rpm for 12 min at room temperature. After that, DNA were extracted by phenol-chloroform-isoamyl alcohol method (Martinez-Fernandez et al 2016).…”