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

Abstract

The effects of disodium fumarate on microbial growth, CH 4 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 NH 3 -N in the cultures. Adding fumarate to batch cultures tended ( P =0·099) to decrease CH 4 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.