Whole-farm systems modelling of greenhouse gas emissions from pastoral suckler beef cow production systems

A whole farm BEEF systems Greenhouse gas Emissions Model (BEEFGEM) was developed to determine the effect of varying management practices on greenhouse gas (GHG) emissions from pastoral beef production systems. BEEFGEM simulates two categories of GHG emissions: firstly, the direct GHG emissions of methane, nitrous oxide and carbon dioxide from on-farm livestock production activities and secondly, indirect GHG emissions associated with inputs used on the farm and GHG emissions associated with nitrate leaching and ammonia volatilisation. The aim of this work was to investigate the effect of alternative production systems at farm level on GHG emissions. Greenhouse gas emissions were modelled for five contrasting beef production systems, one based on average farm conditions in Ireland and four based on research farm conditions. Both direct and total GHG emissions per hectare increased with increasing stocking rate for all scenarios tested. However, increasing stocking rate led to a reduction in GHG emissions per kg beef carcass, albeit with higher levels of production efficiency. At moderate stocking rates, increasing stocking rate further resulted in an increase in GHG emissions per kg beef carcass. Cattle production systems finishing males as bulls had lower GHG emissions than production systems finishing males as steers and thus, the lowest GHG emissions per kg beef carcass were achieved for bull beef production systems at moderate stocking rates which had direct and total system GHG emissions of 15.7 and 18.9 kg CO2e/kg beef carcass, respectively. Bull beef production systems at high stocking rates were most profitable. The highest GHG emissions were for the scenario representing average farm conditions in Ireland with direct and total emissions of 19.0 and 23.1 kg CO2e/kg beef carcass, respectively. This was also the least profitable scenario.

► A whole-farm greenhouse gas (GHG) emissions model of pastoral beef cattle systems was developed.
► Research farm rather than representative Irish farm systems had lower GHG emissions per kg carcass.
► GHG emissions per kg carcass were lower for moderately rather than intensively stocked systems.
► Cattle production systems finishing males as bulls rather than steers had lower GHG emissions.
► Bull beef production systems at high stocking rates were also most profitable.