Degradability of OM was greatest for CAC, followed by CAKC, CKC, and CC irrespective of additives except for CC and CKC diets without any additive, for which degradability was similar between diets containing R:C in the ratio of 70:30. Degradability of OM reduced due to both fumarate and nitrate compared with control for CC, CAKC and CAC, but was not affected for CKC diets. For diets containing R:C ratio of 40:60, OM degradability was highest for CAC, followed by CAKC, CKC and CC in a descending order when no additive was added. However, CC diet only had lower digestibility than other diets when nitrate was included. When fumarate was added, degradability was lowest for CC, followed by CKC, but was similar between CKC and CAKC, and CKC and CAKC. Nitrate decreased OM degradability compared with control, but fumarate did not influence the degradability except for lower digestibility for CC.