Abstract
There is an interest in controlling rumen methanogenesis as an opportunity to both decrease the emissions of greenhouse gases and improve the energy efficiency of rumen fermentation. However, the effects of inhibiting rumen methanogenesis on fermentation are incompletely understood even in in vitro rumen cultures, as the recovery of metabolic hydrogen ([H]) in the main fermentation products consistently decreases with methanogenesis inhibition, evidencing the existence of unaccounted [H] sinks. We hypothesized that inhibiting methanogenesis in rumen batch cultures would redirect [H] towards microbial amino acids (AA) biosynthesis as an alternative [H] sink to methane (CH4). The objective of this experiment was to evaluate the effects of eight inhibitors of methanogenesis on digestion, fermentation and the production of microbial biomass and AA in rumen batch cultures growing on cellulose. Changes in the microbial community composition were also studied using denaturing gradient gel electrophoresis (DGGE). Inhibiting methanogenesis did not cause consistent changes in fermentation or the profile of AA, although the effects caused by the different inhibitors generally associated with the changes in the microbial community that they induced. Under the conditions of this experiment, inhibiting methanogenesis did not increase the importance of microbial AA synthesis as a [H] sink.
Highlights
Ruminants can transform roughages and non-protein nitrogen (N) otherwise unavailable to humans into meat, milk, wool, and traction
The resulting mixture of fluid and solids was subjected to an eggbeater at low speed under O2-free CO2 for 1 min to detach microorganisms adhered to solid particles
Net production of microbial N and amino acids (AA) were calculated by assuming that all N and AA present in the undigested residue corresponded to net microbial synthesis during the incubations, as their initial content was minimized by using pure cellulose as substrate and reducing the amount of inoculum from 20% (v/v) [12] to 0.1%
Summary
Ruminants can transform roughages and non-protein nitrogen (N) otherwise unavailable to humans into meat, milk, wool, and traction Essential to this nutritional flexibility is the presence of a complex microbial community in the rumen, which is able to degrade structural carbohydrates and synthesize amino acids (AA) by incorporating ammonia into carbon chains. It has been proposed that some of the unaccounted [2H] incorporated into the main fermentation products when methanogenesis is inhibited may be explained by increases in microbial biomass production, along with changes in its composition [9]. Our hypothesis was that changes in the synthesis of microbial AA could partly explain the decrease in [2H] recovery in main fermentation products when methanogenesis is inhibited. Under the conditions of this experiment, uptake of [2H] for microbial AA biosynthesis did not explain the consistent decline occurring in [2H] recovery when methanogenesis is inhibited
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