Feeding strategies that may lower methane
From the November 2008 edition of Agriculture Today.
Farm modelling of lamb production systems indicates that focused feeding of high quality conserved forage may reduce total methane emissions and emissions intensity at no net cost, and may have potential to reduce the exposure of farm systems to climate risk.
Results from modelling by NSW Department of Primary Industries’ Cooma livestock officer, Doug Alcock, will need validation with corroborating field data in order for the effects to be included in any formally recognised carbon accounting system.
However, at $30 a tonne CO2 equivalent, the reduction in emissions liability is between two and four dollars per hectare per year for the systems analysed.
At a farm level, emissions are a function of the number of animals, their daily methane output and the time they spend on the farm.
Most prime lambs spend significantly less than a full year on the farm and lambs that reach market weights and are slaughtered sooner produce less total methane.
Mr Alcock checked the methane output of various production feeding strategies using GrassGro - a grazing system model and decision support tool - which uses historical daily weather data to simulate the impact of pasture growth and supplements on animal performance.
He simulated a typical prime lamb enterprise at Wagga Wagga (July lambing at three ewes per hectare) using weather data between 1957 and 2006, and tested the impact of production feeding weaned lambs either grain or silage.
Feeding strategies were called Targeted or Ad lib.
Targeted supplements were fed as required to reach the slaughter weight on February 1; Ad lib supplements were fed when green available herbage mass fell below 1000 kilograms dry matter per hectare (see table).
Total methane from lambs was least from ad lib feeding, falling by 20 per cent and 37pc for silage and grain feeding respectively.
Feeding grain reduced methane more than feeding silage, mostly due to even earlier sale dates but starchy diets also reduce methane yield.
Despite substantial reductions in methane output from lambs, whole farm emissions fell between only four per cent and 11pc, since emissions from breeding ewes increased due to higher autumn feed intake when lambs are sold earlier.
With silage priced at $67/t and grain at $250/t, production feeding only breaks even over the long term - but the strategy does reduce exposure to risk in dry years.
If agriculture is ultimately included in a carbon pollution reduction scheme, these strategies also have the potential to reduce permit liabilities arising from methane emissions.
View graph: Feeding strategies compared to base system
Contact Doug Alcock, Cooma, (02) 6452 3411, doug.alcock@dpi.nsw.gov.au
