Methane production and energy partition of cattle in the tropics.

The aim of this experiment was to determine CH4 production and energy partition for a range of diets fed to Bos indicus cattle. Six Brahman cattle were fed on three different diets in a replicated Latin square experiment over three periods. The diets were (1) long-chopped Angleton grass (Dicanthium aristatum) hay ad libitum (DM digestibility (DMD) 41 (SE 2)%; 4 g N/kg), (2) long-chopped Rhodes grass (Chloris gayana) hay ad libitum (DMD 60 (SE 1)%; 14 g N/kg) or (3) 2 kg long-chopped lucerne (Medicago sativa) hay/d plus a high-grain diet (ad libitum) (DMD 70 (SE 1)%; 31 g N/kg). CH4 production was measured using confinement-type respiration chambers. Metabolizable energy intake (MJ/d) of cattle fed on Angleton grass (18.4 (SE 2.0)) was lower (P < 0.01) than that for Rhodes grass (54.9 (SE 2.1)), which was lower (P <0.01) than that for the high-grain diet (76.7 (SE 5.8)). CH4 production (g/d) for cattle fed on Rhodes grass (257 (SE 14)) was higher (P < 0.01) than that for cattle fed on both the high-grain diet (160 (SE 24)) and Angleton grass (113 (SE 16)). CH4 conversion rate (MJ CH4 produced per 100 MJ gross energy intake) was not significantly different between cattle fed on Angleton (10.4 (SE 1.1)) and Rhodes (11.4 (SE 0.3)) grass, but was higher (P < 0.01) than for cattle fed on the high-grain diet (6.7 (SE 0.7)). CH4 production (g/kg live-weight gain) was associated (P < 0.001) with both live-weight gain and feed:gain ratio. We conclude that the relationships between CH4 production, energy utilization and live-weight change of cattle fed on tropical forages differ from those of cattle fed on diets based on temperate forages.