Effects of disodium fumarate on in vitro rumen microbial growth, methane production and fermentation of diets differing in their forage:concentrate ratio.

The effects of disodium fumarate on microbial growth, CH4 production and fermentation of three diets differing in their forage content (800, 500 and 200 g/kg DM) by rumen micro-organisms in vitro were studied using batch cultures. Rumen contents were collected from four Merino sheep. Disodium fumarate was added to the incubation bottles to achieve final concentrations of 0, 4 and 8 mm-fumarate, and (15)N was used as a microbial marker. Gas production was measured at regular intervals from 0 to 120 h of incubation. Fumarate did not affect (P>0.05) any of the measured gas production parameters. In 17 h incubations, the final pH and the production of acetate and propionate were increased linearly (P<0.001) by the addition of fumarate. Fumarate tended to increase (P=0.076) the organic matter disappearance of the diets and to decrease (P=0.079) the amount of NH3-N in the cultures. Adding fumarate to batch cultures tended (P=0.099) to decrease CH4 production, the mean values of the decrease being 5.4 %, 2.9 % and 3.8 % for the high-, medium- and low-forage diet, respectively. Fumarate tended to increase (P=0.082) rumen microbial growth for the high-forage diet, but no differences (P>0.05) were observed for the other two diets. These results indicate that the effects of fumarate on rumen fermentation depend on the nature of the incubated substrate, the high-forage diet showing the greatest response.