A bioeconomic model was developed to predict outcomes of scenarios to select for methane
efficiency in Merino sheep. The model determines economic values for trait improvement according
to different breeding objectives. A selection index approach is used to predict response to selection,
assuming knowledge or assumptions about genetic parameters, economic values of breeding
objective traits and phenotypic measurement information used to select animals, including
information from reference populations for genomic selection. Breeding objectives were based on
profit per DSE, reduction in overall flock methane output and methane production per kg lamb
produced (defined here as methane efficiency). Results showed that methane production to produce
a certain amount of lambs is affected not only by methane production per head, but also by
reproductive rate. Methane output per kg lamb produced can be decreased by 3.5% per annum, with
the effect of improving production and reproduction efficiency being stronger than the effect of
reducing methane production per head.