Continual refinement of methods estimating enteric methane production in beef finishing cattle provides a more accurate assessment of the environmental impact of the beef industry. The USDA-OCE publication “Quantifying Greenhouse Gas Fluxes in Agriculture and Forestry: Methods for Entity-Scale Inventory” identified conservation practices and management strategies for reducing greenhouse gas emissions while improving agriculture production (Eve et al., 2014). In Chapter 5 a new method to estimate effects of nutrition and management on enteric methane production of feedlot cattle is provided. The system recommends using adjustment factors to correct the IPCC (2006) tier 2 Methane Conversion Factor (Ym) of 3.0% of gross energy intake to an adjusted Ym. Adjustment factors are used for dietary grain and fat concentrations, grain type and processing method, and ionophore use. These adjustment factors let beef producers more accurately determine the enteric methane production associated with their individual finishing operation.
To evaluate this new model, we developed a database consisting of 36 refereed publications, with 75 treatment means. The focus of this database was to identify published research relating to high concentration beef finishing that provided methane as a percent of gross energy, or provided enough information for calculation. Treatments containing greater than 20% forage were excluded, as they are not representative of a high concentration finishing diet. Additionally, treatment diets utilizing a methane mitigation agent were excluded from the database.
This database encompassed 75 treatment means containing a wide range in weight, intake and protein of the diets. Body weight, dry matter intake, and dietary crude protein concentrations for the database ranged from 150 to 723 kg, 4.78 to 12.9 kg, and 9.4 to 23%, respectively. Predicted Ym had a significant but relatively low correlation (r = 0.31, P = 0.0077) to actual Ym. However, when one experiment (4 treatments) with very high methane values (likely a result of manure CH4) was removed, the correlation improved (r = 0.62, P < 0.0001), resulting in the following relationship: Predicted Ym = 2.23 + (0.41 * actual YM) (r2 = 0.39, RMSE = 0.58). Predicted g of CH4 produced daily were highly correlated to actual g of CH4/d (r2 = 0.63, RMSE = 22.61), and predicted CH4 produced, as a percentage of digestible energy intake, was highly correlated to actual CH4 per kcal of digestible energy intake, DEI (r2 = 0.46, RMSE = 0.61). Under the conditions of this investigation, the new model moderately predicted enteric methane production from feedlot cattle fed high-concentrate diets.
The database will be expanded as refereed publications suitable to the selection criteria are identified. Trials with greater forage inclusion will be evaluated to test the robustness of the model and evaluate the correlation to IPPC (2006) estimations.
Tracy D. Jennings, Associate Research Scientist, Texas A&M AgriLife Research
Kristen Johnson, Professor, Washington State University; Luis Tedeschi, Professor, Texas A&M University; Michael Galyean, Provost, Texas Tech University, Richard Todd, Soil Scientist, USDA-ARS; N. Andy Cole, Retired Animal Scientist, USDA-ARS
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