Title: Methane emissions from a beef cattle feedyard during winter and summer on the southern High Plains of Texas Authors
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 19, 2014
Publication Date: N/A
Interpretive Summary: Methane is a powerful greenhouse gas. Beef and dairy cattle produce a lot of methane from a digestive process called enteric fermentation. We want to better understand how much methane that feedyard cattle raised for beef produce so that we can better estimate national inventories of greenhouse gases, improve mathematical descriptions of methane loss and provide accurate estimates for potential regulations. We measured methane loss from a commercial feedyard in the Panhandle of Texas during winter and summer. We found that, on average, each animal in the feedyard produced from 0.18 to 0.21 lb of methane per day. Slightly more methane was produced in the summer because of a change in cattle diet. For every 100 lb of feed that cattle ate, 0.94 lb of methane was lost in winter and 1.1 lb lost in summer. Cattle feed and the methane that cattle produce can also be expressed in terms of the energy they contain. The percentage of total energy eaten that is lost as methane is called the methane conversion rate, or Ym. This percentage is important because it’s a widely recognized way to estimate methane loss from cattle for national inventories of greenhouse gases. We found that Ym ranged from 2.7% to 3.3%, and averaged 3.0%. This confirmed that Ym values currently in use for feedlot fed cattle are reasonable.
Technical Abstract: Methane (CH4) emissions from enteric fermentation by livestock account for about 2.1% of U.S. greenhouse gas emissions, with beef and dairy cattle the most significant sources. A better understanding of CH4 emissions from beef cattle feedyards can help build more accurate emission inventories, improve predictive models, and meet potential regulatory requirements. Our objective was to quantify CH4 emissions during winter and summer at a typical beef cattle feedyard on the southern High Plains in Texas. Methane emissions were quantified during 32 days in winter and 44 days in summer using open path lasers and inverse dispersion analysis. Methane per capita emission rates (PCER) ranged from 71 to 118 g animal -1 d-1 in winter and from 70 to 130 g animal -1 d-1 in summer. Mean CH4 PCER were similar in January, February and May, averaging 85.0 +/- 0.95 g animal -1 d-1, and then increased to 93.4 g animal -1 d-1 during the June-July period. This increase was attributed to increased dietary fiber. Methane loss ranged from 9.2 to 11.4 g CH4 kg-1 DMI, with lower values during winter. Gross energy intake (GEI) ranged from 135.2 to 164.5 MJ animal-1 d-1 and CH4 energy loss ranged from 4.5 to 4.9 MJ animal-1 d-1. Fraction of GEI lost as CH4 (Ym) averaged 2.8% in winter and 3.2% in summer and 3.0% overall. These values confirm Ym currently recommended by the Intergovernmental Panel on Climate Change for Tier 2 estimates of enteric CH4 from feedlot fed cattle.