The Impact on Farm Productivity, Profitability and Predicted Enteric Methane Emissions from Varying Weaning Weight of Lambs on New Zealand Sheep and Beef Farms

The impact of increasing the weaning weight of lambs on the productivity and profitability of sheep enterprises on New Zealand sheep and beef farms has been investigated without considering greenhouse gas emissions. The study examined the impact of increasing the weaning weight of lambs on sheep enterprise productivity, profitability and predicted enteric methane (CH 4 ) emissions in a case study farm using a system dynamic model. Under a fixed feed supply condition, weaning weights of all lambs were increased by 10% and 20% compared to a base scenario. Carcass weight equivalent per hectare rose from 79.9 to 81.7 kg/ha and 91.4 kg/ha, while cash operating surplus per hectare increased from NZD173/ha to NZD184/ha and NZD262/ha, respectively. Predicted enteric CH 4 emissions declined marginally from 566.3 to 563.8 t and 561.0 tonnes of carbon dioxide equivalent (tCO 2 e), while predicted emission intensity reduced from 7.67 kg CO 2 e/kg to 7.53 kg CO 2 e/kg (2.0%) and 7.39 kg CO 2 e/kg liveweight sold (3.6%), respectively. Economic emission efficiency increased to NZD94/tCO 2 e and NZD135/tCO 2 e compared to NZD88/tCO 2 e, respectively. Increased lamb weaning weight improved productivity, profitability and economic and predicted CH 4 emission efficiencies but did not significantly reduce predicted CH 4 emissions under fixed feed supply conditions. This suggests no trade‐off between profits and enteric CH 4 emissions.