As well as affecting the annual maintenance energy requirements of ewes, adult live weight also dictates the energy required to grow replacement stock up to their mature weight. The SIL index estimates that a 1kg decrease in adult weight corresponds to a $0.72 benefit. The Ovita Trait Prioritisation process ranked adult live weight as the second most important trait behind meat yield, with an assumed $127million estimated benefit to the industry based on an average ewe live weight of 62kgs. The calculation assumed there were no negative correlations between a reduction in live weight and ewe fertility, lamb weaning and carcass weights.
In the past adult liveweight has not been well recorded. However, recently this has been changing. Twelve flocks from nine different farms are now in the third year of data collection for adult liveweight. There are also ~65,000 SIL LWMATE (pre-mating ewe liveweights) records from 50 breeders over ~65 flocks, dating from 2008-2011.
Data collected from the twelve flocks above have been used to estimate heritabilities and phenotypic/genotypic correlations in ewe efficiency traits, including adult liveweight.
There are currently no genomic breeding values (GBVs) for adult liveweight. Genomic breeding values are expected to be developed and released in 2012.
How can you help?
To generate GBVs we need sire DNA from Romney, Perendale, Coopworth and especially Texel and composite SIL flocks, where female progeny have been or will be weighed as adults. We would prefer that all breeding ewes from these sires are weighed at least once annually to record LWMATE. Genomic BVs for each of these breeds can then be developed for use. Any breeders interested in contributing please contact John McEwan firstname.lastname@example.org or Lucie Archer email@example.com.
There are currently no specific genetic tests for adult live weight.