Effects of pasture improvement on productivity, gross margin and methane emissions of a grazing sheep enterprise

Abstract

Improving the availability and digestibility of pasture typically increases the enteric methane emission (g/day) produced by ruminants, but reduces the methane yield per unit of meat or wool produced. On Australian farms, sowing of improved pastures is associated with an increase in stocking rate (animals/ha) to manage the sward and repay sowing costs. This increase in animal numbers complicates the calculation of changes in whole-farm enteric methane emissions associated with pasture improvement. The GrassGro™ model was used to simulate the changes in annual methane, meat, wool and gross margin (GM), resulting from sowing improved pasture on a 100 ha cross-bred lamb farm at Cowra, NSW. Simulations used 45 years of local weather data with stocking rates on unimproved and improved pastures of 3.5 and 9 ewes/ha, respectively. Farm methane production and sales of wool and LW were increased 2.3-, 2.7- and 3.1-fold by sowing 100% of the farm area to improved pasture. GM was increased almost four-fold and the annual variation in GM reduced. Consequently, while annual enteric methane emissions on sustainably managed pastures are greater if the pasture is improved, the proportionally greater increase in farm GM and profit far exceeds the potential value of extra emissions.