The Effects of Mature Ewe and Hogget Weaning Rates on Sheep Enterprise Productivity, Profitability, and Enteric Methane Emissions on North Island Hill Country Farms

A system dynamics model of a sheep enterprise on a New Zealand sheep and beef farm was used to concurrently evaluate productivity, profitability, and predicted enteric methane outputs, allowing farmers to make informed decisions about improving mature ewe weaning rates (lambs weaned/ewe mated) or breeding hoggets. Mature ewes were bred at 125%, 140%, and 165% weaning rate scenarios, while hoggets were bred at 0%, 60%, and 80% weaning rate resulting in various combinations (i.e., 125–0, 125−60, or 125–80). Improvements in the weaning rates of mature ewe or breeding hoggets improved kg lamb carcase weight equivalent per ha, and cash operating surplus per ha, due to an increased number of lambs weaned and sold, reduced enteric methane intensity (g methane/kg of product), and increased economic emission efficiency (profits/tCO 2 e). Compared to hogget breeding, achieving a high weaning rate, that is, 165% in mature ewes, provided greater improvements in all indicators than alternatively achieving 140% and 60% or 125% and 80% in mature ewe and hogget weaning rates, respectively. Considering poor weaning rates in hoggets and management complexity, farmers may find it easier to focus on achieving higher weaning rates in mature ewes, rather than breeding hoggets to improve profitability and enteric methane emission efficiency.