Fumaric acid supplements have no effect on methane emissions per unit of feed intake in wether lambs

Recent reports suggest that supplementing the diet of ruminants with up to 10% fumaric acid (FA) can produce large reductions in methane (CH4) emissions, but the results have been equivocal. This trial evaluates the potential of FA to reduce enteric CH4 emissions from 18-month-old wethers fed lucerne. On two occasions, methane emissions were measured on 20 wethers fed a diet of dried ground lucerne with FA added to the diet at 0, 4, 6, 8 and 10 g FA/100 g dry matter (n=4 wethers/treatment). Individual daily CH4 emissions were estimated using the sulfur hexafluoride (SF6) tracer gas technique together with measurements of daily dry matter intake (DMI) and total faecal output. Rumen samples were collected twice during the treatment periods in order to evaluate the effect of FA on rumen pH. There was a significant negative regression between FA% in the diet and CH4 emissions/day. However, the addition of FA did not affect CH4 emissions/kg DMI because high levels of FA supplementation reduced DMI. Rumen pH increased linearly with increasing level of FA supplementation. In conclusion, the effect of FA on CH4 emissions in this trial was associated with the resulting reduction in DMI and there were no decreases in CH4 emissions/kg DMI.