Methane production and soluble carbohydrates in the rumen of sheep in relation to the time of feeding and the effects of short-term intraruminal infusions of unsaturated fatty acids

The daily methane production of sheep given sugar-beet pulp was greater than that of sheep given hay. The rates of methane production on both diets increased during feeding and then decreased to an apparently steady value. When no food was given the rates of methane production continued to fall exponentially with a half-life of about 24 h. 2. Mixtures of unsaturated long-chain fatty acids infused into the rumen during feeding inhibited the production of methane. The inhibition was greater when the sheep were given hay than when they were given sugar-beet pulp. 3. In general the concentration of soluble carbohydrates in the rumen increased during feeding and fell rapidly to the values found before feeding as soon as the sheep finished eating. The infusion of unsaturated fatty acids during feeding did not result in an accumulation of soluble carbohydrate in the rumen. 4. It is suggested that the rapid methane production during feeding was associated with fermentation of the more soluble part of the diet and that the fermentation of carbohydrate was not inhibited by the infused fatty acids. The results are consistent with specific inhibition of methanogenesis by unsaturated fatty acids.