Methane production and energy partition of cattle in the tropics

<jats:p>The aim of this experiment was to determine CH<jats:sub>4</jats:sub>production and energy partition for a range of diets fed to<jats:italic>Bos indicus</jats:italic>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 (<jats:italic>Dicanthium aristatum</jats:italic>) hay<jats:italic>ad libitum</jats:italic>(DM digestibility (DMD) 41 (se 2)%; 4 g N/kg), (2) long-chopped Rhodes grass (<jats:italic>Chloris gayana</jats:italic>) hay<jats:italic>ad libitum</jats:italic>(DMD 60 (se 1)%; 14 g N/kg) or (3) 2 kg long-chopped lucerne (<jats:italic>Medicago sativa</jats:italic>) hay/d plus a high-grain diet (<jats:italic>ad libitum</jats:italic>) (DMD 70 (se 1)%; 31 g N/kg). CH<jats:sub>4</jats:sub>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 (<jats:italic>P</jats:italic>< 0·01) than that for Rhodes grass (54·9 (se 2·1)), which was lower (<jats:italic>P</jats:italic>< 0·01) than that for the high-grain diet (76·7 (se 5·8)). CH<jats:sub>4</jats:sub>production (g/d) for cattle fed on Rhodes grass (257 (se 14)) was higher (<jats:italic>P</jats:italic>< 0·01) than that for cattle fed on both the high-grain diet (160 (se 24)) and Angleton grass (113 (se 16)). CH<jats:sub>4</jats:sub>conversion rate (MJ CH<jats:sub>4</jats:sub>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 (<jats:italic>P</jats:italic>< 0·01) than for cattle fed on the high-grain diet (6·7 (se 0·7)). CH<jats:sub>4</jats:sub>production (g/kg live-weight gain) was associated (<jats:italic>P</jats:italic>< 0·001) with both live-weight gain and feed: gain ratio. We conclude that the relationships between CH<jats:sub>4</jats:sub>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.</jats:p>