In vitro methane emission and acetate:propionate ratio are decreased when artificial stimulation of the rumen wall is combined with increasing grain diets in sheep

The interaction of retention time in the rumen and concentrate diet on methane production in vitro and acetate:propionate ratio was examined. Twenty-four fistulated sheep were used in a complete factorial design with the sheep randomly divided into 4 groups. The sheep had a 5-wk acclimatization period on an oaten chaffdiet, followed by two 3-wk diet phases. Two of the 4 groups were maintained on the oaten chaff diet for the duration of the experiment, with pot scrubbers added to the rumen of 1 of the 2 groups. The remaining 2 groups were offered a low-grain diet (35% grain) in the first diet phase followed by a high-grain diet (70% grain) in the second diet phase. Pot scrubbers were also added to the rumen of 1 of these 2 groups of grain-fed sheep. Pot scrubbers in combination with a low-grain diet decreased the amount of methane produced in vitro from 4.25 to 3.71 mmol/mL of digesta when compared with oaten chaff-fed sheep without pot scrubbers (P < 0.05). The acetate:propionate ratio was 1.6 in sheep fed a high-grain diet with pot scrubbers compared with 2.4 in sheep fed a high-grain diet without pot scrubbers in their rumen (P < 0.05). At high levels of grain, when employing a multivariate statistical analysis including all data, sheep given the combined treatment of grain and pot scrubbers were different from all other sheep groups in this experiment (P < 0.05). Furthermore, sheep fed a high-grain diet were different from sheep receiving the oaten chaffdiets with and without pot scrubbers (P < 0.01 and P < 0.05, respectively). In conclusion, pot scrubbers combined with grain alter the rumen fermentation, and introducing pot scrubbers into the rumens of livestock consuming low levels of grain may be a way to lower methane emissions. Key words: acetate:propionate ratio, methane, methanogen, pH, sheep, volatile fatty acid