FIGURE 5.

Three hypothetical scenarios of manipulation of metabolic hydrogen ([H]) flows in rumen fermentation: (A) Non-intervened rumen fermentation with functional methanogenesis. Methane (CH₄) is the main sink of metabolic hydrogen; (B) Methanogenesis is inhibited with a chemical additive. Part of metabolic hydrogen spared from methane formation is redirected toward alternative sinks that are final fermentation products in the rumen with functional methanogenesis. Redirection of metabolic hydrogen toward alternative sinks is incomplete and the concentration of dissolved dihydrogen increases. The ratio of reduced to oxidized cofactors increases and fermentation, understood as the flow of carbon and the rate of metabolic hydrogen production, is inhibited; (C) A theoretical successful situation in which methanogenesis is inhibited with a chemical additive and an added live hydrogenotrophs redirects a greater proportion of metabolic hydrogen toward alternative sinks potentially beneficial to the host animal. Accumulation of dihydrogen is relieved, cofactors can be re-oxidized as in the rumen with functional methanogenesis, and fermentation is not inhibited.