Numerous mitigation strategies are proposed to reduce greenhouse gas (GHG) emissions from ruminants, with many aimed at reducing enteric CH4. Before implementing such practices, it is critical to evaluate their net impact on total farm GHG emissions. Thus, a life cycle assessment (LCA) was conducted using HOLOS (i.e., a whole farm model based on Intergovernmental Panel on Climate Change methodology modified for Canadian conditions that considers all significant CH4, N2O and CO2 emissions from the farm) to establish whole farm GHG emission intensity for beef production in western Canada (i.e., baseline scenario) as affected by various mitigation practices. Mitigation practices were applied to the baseline scenario and their impacts on the intensity of GHG emissions assessed. Mitigation practices included dietary modifications aimed at reducing CH4 emissions (i.e., changed forage use levels, dietary supplementation with polyunsaturated lipids, use of corn distillers dried grains, improved forage quality) and improved animal husbandry (i.e., increased longevity of breeding stock, improved reproductive performance of the herd). The simulated farm was a beef production operation comprised of 120 cows, 4 bulls, and their progeny, with the progeny fattened in a feedlot. The farm also included cropland and native prairie pasture for grazing to supply the feed required by the herd. The LCA was conducted over 8 years to fully account for lifetime GHG emissions from breeding stock, as well as the progeny raised for market. The baseline scenario estimated the GHG emission intensity of beef production at 22kg CO2 equivalent/kg carcass; 80% of GHG emissions were from the cow calf system and 20% from the feedlot system, with enteric CH4 accounting for 63% of total emissions. Strategies applied to the cow calf herd individually reduced total farm GHG intensity by up to 8% with up to a 17% total reduction possible by combining strategies. In comparison, strategies applied to the feedlot had only a small impact on GHG emissions; reducing total GHG intensity by less than 2% when applied individually or by 3–4% when applied in combination. Although the North American beef production system is already highly efficient, a number of mitigation strategies could be implemented to further lower GHG emissions associated with producing beef, with a total reduction of about 20% attainable if multiple strategies are applied to both the cow herd and the feedlot. However, the biggest reductions in GHG emissions are achieved when mitigation practices target reducing enteric CH4 from the breeding herd. When the grassland in the baseline scenario was newly seeded onto previously cropped land, its soil C gain more than offset all GHG emissions, changing the beef production system from a net emitter to a net sink of C. Although such estimates of soil C gain have uncertainty, this scenario demonstrates that the net GHG balance of a beef production system is powerfully influenced by C dynamics in the associated land base, emphasizing the importance of including these dynamics in assessments of mitigation potential.This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture – Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson.

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