Influence of sodium fumarate addition on rumen fermentation in vitro

The influence of sodium fumarate on rumen fermentation was investigated in vitro using batch and semi-continuous cultures of mixed rumen micro-organisms taken from three sheep receiving a basal diet of hay, barley, molasses, fish meal and a mineral-vitamin supplement (500, 299.5, 100, 91 and 9.5 g/kg DM respectively). Batch cultures consisted of 10 ml strained rumen fluid in 40 ml anaerobic buffer containing 200 mg of the same feed given to the sheep. Sodium fumarate was added to achieve a final concentration of 0, 5 or 10 mmol/l, as a result of the addition of 0, 250 or 500 µmol, equivalent to 0, 200 and 400 g/kg feed. CH production at 24 h (360 µmol in the control cultures) fell (P <0.05) by 18 and 22 µmol respectively (SED 7.5). Total gas production was increased by the addition of fumarate without significant accumulation of H. Substantial increases in acetate production (92 and 194 µmol; SED 26.7, P <0.01) were accompanied by increases in propionate formation (212 and 396 µmol; SED 13.0, P <0.001). Longer-term effects of fumarate supplementation on ruminal fermentation and CH production were investigated using the rumen simulation technique (Rusitec). Eight vessels were given 20 g basal diet/d, and half of them received a supplement of fumarate (disodium salt) over a period of 19 d. The response to the daily addition of 6.25 mmol sodium fumarate was a decrease in CH production of 1.2 mmol (SED 0.39, P <0.05), equivalent to the consumption of 4.8 mmol H, and an increase in propionate production of 4.9 mmol (from 10.4 to 15.3 (SED 1.05) mmol/d, P <0.01). The inhibition of CH production did not decline during the period of time that fumarate was added to the vessels. Thus, the decrease in CH corresponded well to the fraction of the fumarate that was converted to propionate. Fumarate had no significant (P > 0.05) effect on total bacterial numbers or on the number of methanogenic archaea, but numbers of cellulolytic bacteria were increased (8.8 v. 23.9 (SED 2.49) x 10 per ml, P <0 01). Fumarate also increased DM digestibility of the basal diet after 48 h incubation (0.476 v. 0508 (SED 0.0123), P <0 05). Thus, it was concluded that sodium fumarate may be a useful dietary additive for ruminants, because it diverts some H from CH production and because it is able to stimulate proliferation of cellulolytic bacteria and digestion of fibre.