Methane production (ml/g DM) was lowest due to inclusion of nitrate for all the diets with R:C ratio of 70:30, which was also true when methane production was expressed as ml/g of digestible OM. Methane production (ml/g DM) was significantly lower (P < 0.05) due to addition of fumarate for the CC and CAKC diets, but not for the CAC and CKC, than control. This trend was only observed for CAKC when methane production was expressed as ml/g DM. CKC diet produced lower methane than other diets containing no additive. CKC diet also produced less methane than CC diet, but CAKC and CAC diet produced greater amount of methane than other diets with inclusion of both nitrate and fumarate. Methane production (ml/g digestible OM) was lowest for CKC, followed by CAC and then CC and CAKC with or without additives ( Fig. 1).