Rumen microbiome response to different levels of bromoform in sheep

Bromoform is a methane inhibitor and the major active component in the seaweed genus Asparagopsis. In order to determine the effect of bromoform on the rumen microbiome a trial with 30 sheep (n=5) was conducted where different doses of bromoform (0, 4.3, 13 and 39 mg/d) were fed for 17 days. In addition the highest dose was also fed once every three days. Rumen gases were quantified in respiration chambers and rumen samples collected after chamber measurements and were analyzed for metabolites and their microbial community composition.

Relative the control, methane emissions were decreased linearly by 10, 30 and 90%, while hydrogen emissions increased. The medium dose and the high dose offered every three days showed similar 30 % methane inhibition. Despite the decreased methane and increased hydrogen emissions no effect on the proportion of the volatile fatty acids, alcohols formate lactate or succinate was observed for the low and medium treatments. Only with the highest daily bromoform dose the proportion of propionate in the rumen was 10% higher compared to the control at the expense of acetate. and low concentrations of formate accumulated. Metabolomic and microbial community analysis is underway to elucidate the changes in rumen function and especially fate of hydrogen during methane inhibition in the rumen

Our data suggest that at 30 % methane inhibition hydrogen removal in sheep does not involve the standard hydrogen removal pathways described in literature.