The present invention concerns the reduction of gastro-intestinal methanogenesis in ruminants with the aid of agents that compete for the hydrogen atoms required by methanogens during normal fermentation of ingested feed. The invention in one aspect resides in the findings that both nitrate reductive pathways as well as sulphate reductive pathways outcompete gastro-intestinal methanogenesis in ruminants and, that the methanogenesis reducing effects of nitrate and sulphate are completely additive. At the same time the combined administration of nitrate and sulphate was found to be fully effective to avoid or mitigate the potential problems of nitrite intoxication normally encountered when using nitrate alone, which effect is further enhanced, where necessary, by the addition of a nitrite reducing probiotic micoroorganism. Hence, products are provided comprising high amounts of a combination of a nitrate compound and a sulphate compound and optionally a nitrite reducing probiotic microorganism, as well as methods of reducing gastro-intestinal methanogenesis in ruminants using such compositions.