Effect of progressive inoculation of fauna-free sheep with holotrich protozoa and total-fauna on rumen fermentation, microbial diversity and methane emissions

Abstract

Rumen methanogenesis represents an energy waste for the ruminant and an important source of greenhouse gas; thus, integrated studies are needed to fully understand this process. Eight fauna-free sheep were used to investigate the effect of successive inoculation with holotrich protozoa then with total fauna on rumen methanogenesis. Holotrichs inoculation neither altered rumen fermentation rate nor diet digestibility, but increased concentrations of acetate (+15%), butyrate (+57%), anaerobic fungi (+0.82 log), methanogens (+0.41 log) and methanogenesis (+54%). Further inoculation with total fauna increased rumen concentrations of protozoa (+1.0 log), bacteria (+0.29 log), anaerobic fungi (+0.78 log), VFA (+8%), ammonia and fibre digestibility (+17%) without affecting levels of methanogens or methanogenesis. Rumen methanogens population was fairly stable in terms of structure and diversity, while the bacterial community was highly affected by the treatments. Inoculation with holotrich protozoa increased bacterial diversity. Further inoculation with total fauna lowered bacterial diversity but increased concentrations of certain propionate and lactate-producing bacteria, suggesting that alternative H2 sinks could be relevant. This experiment suggests that holotrich protozoa have a greater impact on rumen methanogenesis than entodiniomorphids. Thus, further research is warranted to understand the effect of holotrich protozoa on methane formation and evaluate their elimination from the rumen as a potential methane mitigation strategy.

Keywords: entodiniomorphids; fermentation; holotrichs; methanogenesis; methanogens; rumen protozoa.

Methane emissions from ruminants represent a concern of global magnitude. Understanding the interactions of different rumen protozoa with bacteria and methanogens is vital to develop adequate methane mitigation strategies.

Figure 1.

Canonical correspondence analysis illustrating the relationship between the structure of the bacterial (A) or methanogen communities (B) with the rumen function. Treatment's names indicate the centroid of each treatment. Arrows show the direction of the gradient and their length is proportional to the correlation. Arrows longer than the dotted circle are significant (P < 0.05). Treatments: FF, fauna-free; HOL, Holotrich monofaunated; FAU, total-faunated sheep. Animals are indicated with numbers.