Twelve local “Yellow” cattle with initial weight from 114 to 117kg and 1.8 to 2 years of age were allocated in a completely randomized block design of 4 treatments and 3 replicates. The treatments (as supplements to ad libitum cassava pulp plus 3% urea on DM basis and rice straw 1% of LW) were: cassava foliage and brewers’ grains in the ratio 4; 0, 3:1, 2:2 and 0:4 as % of live weight, fresh basis. The experiment was carried out for 120 days from February to July 2016. At the end of the trial, concentrations of methane and carbon dioxide were determined in eructed gas mixed with air in a closed chamber in which the animals were kept for 20 minutes prior to measurement of the gases. There was a quadratic relationship between the rate of live weight and the proportion of brewers’ grains in the diet DM, with the maximum growth rate being recorded when the brewers’ grains provided 9-17% of the diet DM. There was a similar relationship between level of brewers’ grains and DM feed conversion. The ratio of methane to carbon dioxide in mixed eructed gas and air declined with a curvilinear trend as the fresh cassava foliage replaced brewers’ grains in the diet.