Mitigation of greenhouse gas emissions in pasture-based dairy-beef production systems

Abstract

CONTEXTAgriculture and food systems contribute significantly to climate change. Greenhouse gas (GHG) emissions intensity from beef production are high when compared to other livestock production systems and, therefore, mitigation of these emissions is urgently required. In many countries dairy-beef is making a large and growing contribution to total beef output thereby reducing net emissions given the lower emissions intensity of beef originating from the dairy herd when compared to specialized beef-cow systems. GHG emissions from dairy-beef systems can be further reduced by adopting best practice and mitigation technologies. OBJECTIVESThe objectives of this study were to (1) evaluate a range of management practices to reduce GHG emissions for pasture-based beef cattle production systems, (2) model the individual and combined impacts of these management practices on GHG emissions from dairy-beef systems, and (3) identify any trade-offs between GHG emissions mitigation, farm profitability, food security and land use. METHODSA farm level bioeconomic systems model was modified to evaluate spring-born, steer production systems finishing cattle at differing slaughter ages and from contrasting forage-based finishing diets (grazed grass or grass silage, each supplemented with concentrates). Mitigation measures included earlier slaughter age, optimal slurry management, urease inhibitors for nitrogen (N) fertilizers, replacing cereals with ‘by-products’ in concentrate feed rations and incorporating clover in grassland pastures. RESULTS AND CONCLUSIONSCombining mitigation strategies reduced dairy-beef systems GHG emissions intensity by an average of 21%. Incorporating clover in grassland pastures was found to be the most profitable stand-alone mitigation strategy increasing net margin by an average of 18%. Substituting by-products for barley in a concentrate ration converted all systems into net producers of human edible protein; otherwise, steer systems finishing at pasture during the third grazing season were the only net producers of human-edible protein. However, finishing at pasture during the third grazing season increased GHG emissions per animal and per kilogram of beef carcass. SIGNIFICANCEWithin a grass-based dairy-beef system, such as that modelled in this study, a number of complementary GHG emissions mitigation strategies can be implemented, without making substantive changes to the production system, while simultaneously improving farm profitability.