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Nitrous oxide (N2O) is a greenhouse gas with a higher global warming potential than carbon dioxide (CO2) or methane (CH4). The objectives of this research were to quantify enteric N2O emissions from beef cattle and determine effects of dietary nitrate (NO3) concentrations. Experiments consisted of one in vitro incubation trial and 2 live animal (LA) trials. During the in vitro trial, gas was collected from 4 forage-based and 5 corn-based diets. During the LA trials, emissions were monitored from steers in respiration chambers. In LA trial 1, 5 measurements of 256 to 720 min were conducted on a single steer within a 48-h period. In LA trial 2, measurements were conducted on 4 steers in the absence of manure. Highest in vitro N2O production was from diets containing added NO3 or alfalfa. In vitro N2O increased with dietary NO3 concentrations (r2 = 0.99), with little correlation to dietary CP (r2 = 0.17). Added NO3 decreased CH4 emissions. Mean N2O emission rates (±SD) from the LA trials were 6.93 ± 2.99 mg of N2O∙kg−1 of DMI in trial 1 and 2.20 ± 0.10 mg of N2O∙kg−1 of DMI in trial 2. Mean enteric N2O emissions accounted for 0.35% (LA trial 1) and 0.12% (LA trial 2) of CO2 equivalents. Enteric N2O emission rates were 6 to 40 times lower than values cited in earlier publications. Enteric N2O emission rates were also 58 to 108 times lower than manure emissions. Therefore, efforts to reduce greenhouse gas emissions from beef cattle should focus on enteric CH4 and manure N2O as opposed to enteric N2O. |
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