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This study was conducted to evaluate the dietary supplemental effects of 2-nitroethanol (NEOH) in comparison with monensin on methane (CH₄) emission, growth performance and carcass characteristics in female lambs. Sixty female, small-tailed Chinese Han lambs (3.5 ± 0.3 month) were randomly allotted into three dietary treatment groups: (1) Control group, a basal control diet, (2) monensin group, the basal diet added with 40 mg/kg monensin, (3) NEOH group, the basal diet added with 277 mg/kg nitroethanol, and the feedlotting trial lasted for 70 days. Although dietary addition of monensin and NEOH did not affect nutrient digestibility of lambs, both monensin and NEOH decreased the calculated CH₄ production (12.7% vs. 17.4% decrease; <i>p</i> < 0.01). In addition, the CH₄ production represents less dietary energy loss in the monensin and NEOH group than in the control, indicating that monensin and NEOH are potent CH₄ inhibitors that can reduce dietary energy loss. Dietary addition of monensin and NEOH decreased dry matter intake (<i>p</i> < 0.01); however, they increased the ADG of female lambs (<i>p</i> < 0.01). As a result, both monensin and NEOH increased feed conversion efficiency of the feedlotting lambs (<i>p</i> < 0.01), suggesting that feed energy saved from CH₄ production promoted the feed efficiency and ADG in the present study. Except for the fact that NEOH addition increased the net muscle percentage to carcass weight (<i>p</i> = 0.03), neither monensin nor NEOH had a significant influence on carcass characteristics of female lambs (<i>p</i> > 0.05). From an economic point of view, NEOH and monensin caused a reduction in feed consumption costs, therefore resulting in a higher net revenue and economic efficiency than the control. In summary, dietary supplementation of NEOH in comparison with monensin presented a more promoting effect on energy utilization in female lambs by inhibiting rumen methanogenesis more efficiently, and NEOH improved the net revenue and economic efficiency more significantly than monensin.