The aim of the present study was to assess enteric methane (CH4) emissions by crossbred heifers fed a basal ration of low-quality tropical grass supplemented with different nitrogen sources. Four crossbred heifers (Bos taurus × Bos indicus) with an average live weight (LW) of 355 ± 6.01 kg were used in a 4 × 4 crossover Latin square design with four periods of fifteen days each. Basal ration was chopped low-quality tropical grass Pennisetum purpureum fed to cover ~70% of metabolizable energy requirements for maintenance of heifers and it was supplemented with either poultry litter (control ration, T1), urea (T2), canola meal (T3) or soybean meal (T4). Enteric CH4 emissions of heifers were measured in open-circuit respiration chambers for 23 hours. Dry matter (DM), neutral detergent fibre (NDF) and acid detergent fibre (ADF) intakes decreased when feeding urea (1.6% of ration) as a source of nitrogen (7.64, 3.78, and 1.83 kg/d, respectively). Rations including urea (T2) or canola meal (T3) given to heifers fed a basal ration of low-quality Pennisetum purpureum grass significantly reduced acetic acid concentration and increased propionic acid concentration in the rumen and decreased the loss of gross energy as methane (P = 0.004). Incorporation of urea or canola meal in the ration of cattle fed low-quality tropical grass can decrease methane emissions and improve rumen fermentation patterns.
