317 - Importance and Difficulty of Measuring Complete Greenhouse Gas Flux from Diverse Beef Production Systems

Abstract: Cattle naturally respire CO₂ from energy and rumen metabolism, and produce enteric CH₄ from rumen fermentation. In addition, N₂O is produced from soils used for agricultural production following precipitation events. These three gases need to be more accurately quantified in beef production systems to model greenhouse gas (GHG) flux and establish effective mitigation strategies. Most models assume CO₂ respiration equals carbon uptake by soil when cattle are fed harvested feeds or during grazing. Therefore, CH₄ or N₂O release is the net contribution from beef production, while ignoring respired CO₂. Recent evidence suggests carbon uptake in soils within grazing systems may offset much of the GHG emissions during beef production. However, total flux is difficult to measure in open, extensive systems including pasture and feedlot pens. Using methods of eddy covariance, footprint modeling, and satellite GPS data on cattle location during grazing, we have estimated CO₂ and CH₄ production from grazing cattle independent of the pasture (soil and plant) to get accurate fluxes. Regardless of whether the beef industry is already net zero, focus on mitigating enteric methane production is warranted. Three primary methods are used for evaluating CH₄: in vitro techniques, calorimetry head boxes, or pen chambers. The most robust system for quantification of enteric methane is pen chambers, which allows for cattle performance to be evaluated simultaneously. Many new additives are being evaluated, but not yet approved for use in food animals. Use of pen-based chambers has a limitation with large numbers of animals that cannot enter the food chain. More focus is required to find suitable methane mitigation strategies from novel feed additives and evaluate changes in productivity and ensuring no residues. Whenever possible, increasing speed of approval for those additives that are effective and pose no risk for food safety will be critical for ruminant production.