The objectives of the present work were to evaluate the in vivo antimethanogenic effects of Cymbopogon citratus (CC), Matricaria chamomilla (MC) and Cosmos bipinnatus (CB) on beef cattle fed a high in concentrate diet (forage-to-concentrate ratio [F:C] of 19.4:80.6), and the effects of increasing levels of CC (0%, 2%, 3%, and 4% of the daily DM intake (DMI)) on enteric CH4 emissions by beef cattle fed a ration low in concentrate (F:C ratio of 49.3:50.7). Two experiments were conducted to address the objectives. For the first experiment, eight Charolais × Brown Swiss steers distributed in a replicated 4 × 4 Latin square experimental design were used. Four treatments were evaluated: (1) control diet (CO), (2) CO + 365 g dry matter (DM)/d CB, (3) CO + 365 g DM/d MC, (4) CO + 100 g DM/d CC. For Experiment 2, four Charolais x Brown Swiss steers distributed in a single 4 × 4 Latin square design were used. It was concluded that 100 g DM per day CC and 365 g DM per day CB (Experiment 1) reduced CH4 yield of beef cattle. In Experiment 2, CC supplementation levels exceeding 2% of DMI reduced daily CH4 emissions but at the expense of decreasing digestibility of DM.
Keywords: Cosmos bipinnatus; Cymbopogon citratus; Matricaria chamomilla; beef cattle; methane; mitigation.