2012 SIL index changes
SIL proposes to change weightings in SIL standard indexes for DP & TS sheep.
SIL proposes to update indexes in the spring (Sep/Oct) for Dual Purpose (DP or ewe breed) and Terminal SIre (TS or meat breed) sheep. This update takes account of three things;
- Revised pricing for farm costs and farm returns
- Development of models for how these influence total farm profit
- The addition or revision of eBVs for some traits
Current indexes were introduced in 2007. It is timely to update them for todays markets and with an eye to future markets.
Models for the value of number of lambs born and of lamb survival that are behind the current indexes needed revision to account for the interaction between these variables i.e. lamb survival is more important as average litter size or lambing percentage increases. As well, national lambing percentage has increased.
In regard to the penalty SIL applies to adult ewe size for DP sheep (DPA sub-index based on EWT eBV), SIL commissioned a rigorous review of the cost of carrying heavier ewes. We know that selection for lamb growth is very likely to increase size of adult sheep. We believe the revised weighting better reflects the cost of carryng heavier ewes than did the figure currently in use. SIL advocates the measurement of ewe liveweights for all DP sheep flocks.
Since 2007, SIL has completely revised how eBVs are generated in the Dag Score evaluation module, and this led to new weightings being introduced for the Dag Score subindexes (DPD & TSD) late in 2011. Those new weightings were part of the proposed weight change report and so will not change in Sep/Oct 2012.
SIL now has a sub-index for DP Resilience (DPZ), so this can be incorporated into SIL DP Overall (DPO) indexes.
More detail of the changes can be found in the following document.
Users should note that standard SIL indexes are true economic indexes and so the weightings on different traits are a function of the weightings on other, related traits. Selectively using some SIL eBVs with these weightings, while dropping others, will result in a sub-optimal response and restrict genetic gain in economic terms.
Queries about SIL indexes and the proposed changes should be directed to silhelp (tel 0800-silhelp or email firstname.lastname@example.org).