The introduction of an emissions trading scheme means farmers are likely to incur some form of carbon tax on methane emissions. Consequently, it is important to explore management options that could reduce methane output per unit of product sold. A computer model was developed to test a range of management strategies on methane production, relative to farm output. These included changing ewe live weight, conception rate, scanning percentage, ewe and lamb survival, ewe culling rates, lamb growth rate, hogget lambing and ewe culling age. The dataset used to develop the model contains 6,000 ewe and 8,100 lamb records collected over 8 years. The reference flock used in the model comprised 1,000 ewes plus replacements, 1,378 lambs scanned, 989 lambs sold and 288 replacements kept. The carbon cost was 15.99 kg of methane per lamb sold. Three of the most significant influences on methane production per lamb sold were increasing ewe cull age from 5 to 6 years (4.6% reduction), increasing ewe scanning percentage from 160% to 180% (7.8% reduction) and hogget lambing (11.7% reduction). Effects were not completely additive. The model allows methane output to be estimated for any defined production system and quantifies the most effective management changes to minimise methane production on an individual farm or across the wider industry.

GJ, Cruickshank, BC Thomson, and PD Muir

Proceedings of the New Zealand Society of Animal Production, Volume 69, Christchurch, 170-173, 2009
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