Influence of different concentrations of disodium fumarate on methane production and fermentation of concentrate feeds by rumen micro-organisms in vitro.

Batch cultures of mixed rumen micro-organisms were used to study the effects of different concentrations of disodium fumarate on the fermentation of five concentrate feeds (maize, barley, wheat, sorghum and cassava meal). Rumen contents were collected from four Merino sheep fed lucerne hay ad libitum and supplemented with 300 g concentrate/d. Disodium fumarate was added to the incubation bottles to achieve final concentrations of 0, 4, 7 and 10 mM-fumarate. In 17 h incubations, the final pH and total volatile fatty acid production increased (P<0.001) linearly for all substrates as fumarate concentration increased from 0 to 10 mm. Propionate and acetate production increased (P<0.05), while the value of the acetate:propionate ratio decreased (P<0.05) linearly with increasing doses of fumarate. In contrast, l-lactate and NH3-N concentrations in the cultures were not affected (P>0.05) by the addition of fumarate. For all substrates, fumarate treatment decreased (P<0.05) CH4 production, the mean values of the decrease being 2.3, 3.8 and 4.8 % for concentrations of 4, 7 and 10 mM-fumarate respectively. Addition of fumarate did not affect (P>0.05) the total gas production. If the results of the present experiment are confirmed in vivo, fumarate could be used as a feed additive for ruminant animals fed high proportions of cereal grains, because it increased pH, acetate and propionate production and it decreased CH4 production.