Beef cattle production systems are the largest contributors of greenhouse gas (GHG) and ammonia (NH 3 ) emissions in the livestock industry. Here, we present the first meta-analysis and integrated assessment of gaseous emissions and mitigation potentials for a typical beef cattle feedlot system, including methane (CH 4 ), nitrous oxide (N 2 O), and NH 3 losses from enteric fermentation and manure management based on data from 104 studies. A total of 14 integrated emission factors (EF) and the mitigation efficiencies (ME) of 17 available options were provided. The estimated GHG and NH 3 emissions from the baseline feedlot system were 2786 ± 108 kg carbon dioxide equivalents (CO 2 -eq) per animal unit (AU) per year and 49.1 ± 1.5 kg NH 3 AU –1 year –1, respectively. Enteric CH 4 fermentation and manure on the feedlot contributed 67.5% and 80.8% of the total system GHG and NH 3 emissions, respectively. The highest ME values were found for lipid additives for enteric CH 4 fermentation and urease inhibitor additives (UI) for NH 3 emissions from manure on the feedlot, being −14.9% ( p < 0.05) and −59.5% ( p < 0.001), respectively. The recommended mitigation combinations of a low-crude-protein (CP) diet and a UI additive for manure on the feedlot could reduce the GHG of the system by 4.9% and NH 3 by 50.9%. The results of this study have important implications for developing sustainable beef cattle feedlot systems from the viewpoint of GHG and NH 3 mitigation.
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Wang et al. (2018) studied this question.