A partial life cycle assessment of the greenhouse gas mitigation potential of feeding 3-nitrooxypropanol and nitrate to cattle

Agricultural industries are faced with the challenge to reduce their emissions of greenhouse gases (GHG) such as nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4). Approximately 27% of the GHG emissions generated by agriculture and 80% of the GHG emissions generated by livestock are in the form of CH4 from enteric fermentation and manure management. Two feed additives that have been shown to decrease enteric CH4 emissions are 3-nitrooxypropanol (3-NOP) and nitrate. However, data are lacking on the net impact of these CH4 mitigating additives on whole farm GHG emissions across different production systems. The objectives of this partial life cycle assessment (LCA) were: 1) to analyse the effect of 3-NOP and nitrate on whole farm GHG emissions of Australian and Canadian beef and dairy farms, and 2) to analyse the effect of different strategies of 3-NOP and nitrate feeding on whole farm GHG emissions. Two Australian dairy farms (ADF), one Australian beef farm (ABF), one Canadian dairy farm (CDF) and one Canadian beef farm (CBF) were modelled over the productive lifespans of dairy and beef herds. Australian farm GHG emissions were estimated based on the Australian National Greenhouse Gas Inventory method using the Greenhouse Accounting Framework calculators for beef and dairy. For the Canadian farms, total GHG emissions were estimated using Holos 3.0.3, a whole-farm software model. For all farms, the system boundary of the partial LCA was defined as the farm gate, including emissions associated with on-farm activities and emissions associated with production and transport of major production inputs. Both additives decreased whole farm GHG emissions; however, 3-NOP had a greater effect than nitrate. Feeding 3-NOP but not nitrate could be economical for both beef and dairy farms, depending on the cost of 3-NOP. It is concluded that 3-NOP can make an important contribution to reducing whole farm GHG emissions; however, a carbon offset method would have to be in place to incentivize its use in the livestock industries.