Manipulation of rumen methanogenesis by the combination of nitrate with β1-4 galacto-oligosaccharides or nisin in sheep

Effects of β1-4 galacto-oligosaccharides (GOS) or nisin in combination with nitrate were assessed on rumen methanogenesis, intoxication by nitrate, and metabolic rate in nitrate-treated sheep. Four rumen-fistulated wethers were allocated in a 4×4 Latin square design. Nitrate (1.3 g NaNO3/kg0.75 of body weight (BW)), with and without β1-4 galacto-oligosaccharides or nisin was administered into the rumen through a fistula 30 min after the morning meal as a single dose, whereas, β1-4 galacto-oligosaccharides (20 g per day) or nisin (3 mg/kg0.75 of BW per day) was supplemented by sprinkling it onto the feed. Physiological saline was used as control treatment. When compared to saline, nitrate alone markedly lowered rumen methane production and caused a marked accumulation of rumen and plasma nitrite, and formation of blood methemoglobin consequently reduced oxygen consumption, carbon dioxide production, and metabolic rate. As compared to nitrate alone, simultaneous administration of nitrate with β1-4 galacto-oligosaccharides or nisin lowered the concentration of rumen and plasma nitrite and methemoglobin, while keeping rumen methanogenesis at a low level. A relatively higher rate of oxygen consumption, carbon dioxide production, and metabolic rate of sheep given nitrate plus nisin was observed versus that in sheep given nitrate alone. Therefore, an appropriate combination of nitrate with β1-4 galacto-oligosaccharides or nisin might be effective manipulators to abate rumen methanogenesis without nitrate intoxication in ruminants.