Mitigating GHG Emissions from Beef Cattle Housing.

Beef cattle are potential sources of greenhouse gases (GHG).   These emissions include methane produced by fermentation within the gut (enteric), and methane and nitrous oxide emissions from manure.  Life Cycle Analysis of North American (NA) beef cattle production systems consistently indicate that approximately  55 to 63% of total NA beef cattle emissions (in CO₂ equivalents) is from enteric methane,  18 to 23 % is from manure methane and nitrous oxide, and 14 to 24% is from indirect emissions and energy use (feed production, fossil fuel use, manufacturing, etc.).   Approximately 64 to 82% of GHG emissions are from the cow herd, about 17 % from stockers grazing on pastures, and 12 to 16% are from cattle in feedlots fed high –concentrate or high-byproduct diets.   A few studies suggest animals can be genetically selected for lower GHG emissions; however, other studies are contradictory.  The diet fed to cattle affects GHG emissions via modifying microbial fermentation in the gut and nutrient excretion.  For example, increasing dietary protein concentration increases nitrogen excretion, ammonia emissions, and potentially direct and indirect N2O emissions.  Feeding higher grain (i.e. starch) diets, processing feed grains so they are more digestible (i.e. steam flaking vs dry rolling), or adding supplemental fat to the diet (as fat or oil or in high-fat byproducts such as distiller’s grains) significantly decreases enteric methane emissions.  Preliminary data at our lab suggests that providing supplemental protein to cattle on a low- quality forage may increase total enteric methane production (due to increased feed intake and increased ruminal fermentation) but decreases enteric methane production as a % of energy intake or per kg of dry matter intake.  Although dietary factors can affect GHG emissions, in some cases making major modifications to diets is difficult because of logistics, costs, risk  and adverse effects on animal performance.