Maximising energy-yielding rumen pathways in response to methane inhibition

Summary

​Methane represents a direct loss of energy that could be used for increased production if the energy was redirected into live weight gain. Management of hydrogen and methane production in the rumen is an important factor to be considered, when developing strategies to reduce greenhouse gas emissions and improve efficiency of energy utilization from feed. This project has undertaken studies in cattle using a specific methanogen inhibitor (chloroform in a cyclodextrin matrix) to analyse the effect on methane production, metabolic hydrogen flux and subsequent responses in short chain fatty acid (SCFA) production, metabolites and rumen microbial community structure.

The first in vivo experiment using three levels of chloroform-CD (low, medium and high dose) and two diets (hay and forage:concentrate diet), showed a progressively methane reduction when doses of chloroform were increased on both diets. Conversely hydrogen expelled by treated animals increased as methane production was reduced, with the greatest amounts of hydrogen loss occurring in animals supplemented with the hay/concentrate diet. The rumen fermentation parameters showed a shift in the fermentation pathways towards a more propionic acid production in the rumen of animals receiving chloroform with both diets. In relation to the rumen microbial community, there was a reduction in the relative abundance of some methanogen species (e.g Methanobrevibacter) when methane was reduced and an increase in Prevotella species. The microbial community PCoA plots show that samples from animals treated with chloroform were grouped separately from the control samples, showing a dose response.

The results observed were in accordance with previous studies using bromochloromethane as antimethanogenic compound in small ruminants (Mitsumori et al., 2012). Therefore, dietary strategies were tested to facilitate the consumption of this hydrogen excess for improving energy supply to the animal.

The second in vivo trial to identify dietary supplements/microbial treatments that direct excess hydrogen in the rumen into energy yielding products was completed in 2014. Eight fistulated steers were fed a high fermentable concentrate diet with a ratio 60:40 hay:concentrate. The chloroform in a cyclodextrin  matrix was provided progressively to the animals, after 21 days of treatment 4 animals received the supplement phloroglucinol + chloroform during 16 days, while the rest of the animals received the same dose of chloroform. After a 10 d wash out period (for phloroglucinol), 4 animals were inoculated in the rumen with an acetogenic bacteria + chloroform during five days, while the rest of the animals received the same dose of chloroform.

Methane production (g) per kg of DMI was reduced and hydrogen expelled increased with the dose of chloroform as expected. Significant differences were observed on those animals treated with phloroglucinol + chloroform compared with the positive control group that received just chloroform. The hydrogen production (g) per kg of DMI was significantly decreased on the phloroglucinol group compared with chloroform group. The rumen fermentation parameters showed a shift towards more acetic acid production in the rumen of animals treated with phloroglucinol + chloroform.

These results are in accordance with previous studies using phloroglucinol in ruminants, which observed an increased in acetic acid concentration (Tsai and Jones, 1975, Krumholz and Bryant, 1986, Murdiati et al., 1992). That increase suggested a redirection of the excess of hydrogen in the rumen towards acetic acid production by reductive dehydroxylation of phenolic compounds. In relation to the rumen microbial community, OTUs assigned to Coprococcus genus were positively increased by phloroglucinol treatment.