Breeding for reduced methane emissions in extensive UK sheep systems

Abstract

Selection index theory was used to model the effects of methane (CH₄) production in the breeding objective on genetic responses in Scottish Blackface sheep in hill production systems in the UK. A range of economic values (EVs) were assumed for CH₄ production calculated from possible carbon prices (£/t CO₂ equivalent (CO₂-e)). The implicit price of carbon required for maintenance of CH₄ levels or to reduce CH₄ production by 0.1 kg/head/yr in a hill flock was calculated. The predicted genetic changes in CH₄ production from current selection programmes that have an implicit methane EV of zero were calculated. Correlations between production traits and CH₄ production were sampled from assumed normal distributions, as these correlations are currently unknown. Methane emissions are likely to increase at a rate of c. 3 kg CO₂-e/ewe/yr as a result of using current industry selection indices in hill sheep farming systems in the UK. Breeding objectives for more productive hill sheep include reducing lamb losses and rearing more, heavier lambs. By placing a cost on carbon emissions to halt the genetic increase in methane, heavy penalties will be incurred by farmers in terms of reduced productivity. This amounts to £6/ewe/yr or a 5% discounted loss of £2851 per 100 ewe flock over a 10-year selection horizon. If the correlations between production traits and CH₄ are positive (as expected) then an implicit carbon price of c. £272/t CO₂-e is required for no genetic increase in CH₄ production if methane is not measured and c. £50/t CO₂-e if methane could be measured. Achievement of government targets for the whole economy of a 20% reduction in greenhouse gases (GHGs) over a 30-year period would require carbon prices (/t CO₂-e) of £1396 (indirect selection) or £296 (direct selection) for the sheep industry to achieve a 20% reduction entirely via a genetic change of c. -0.1 kg methane/head/yr. These carbon prices are placed in the context of possible government policies. A combination of genetic and non-genetic measures will probably be required for cost-effective reduction in methane production to meet government targets.