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Otago Coopworth Sheep Breeders Club Explanation of Indexes |
SIL Indexes and sub-indexes - genetic merit at a glance.
SIL (Sheep Improvement Ltd) summaries genetic merit in economic terms based on "cents per ewe lambing'. This is done with a "Dual-Purpose Overall Index (DPO)" for Coopworth sheep. To help buyers focus on the relative merits of rams for different characteristics, SIL can produce sub-indexes of the overall index. Each sub-index focuses on a particular trait and uses breeding values (our best-bet estimate of genetic merit) for key traits affecting economic returns to the farmer.
The six sub-indexes SIL offers are GROWTH, MEAT, WOOL, REPRODUCTION, SURVIVAL and DISEASE.
GROWTH considers weaning weight, a later live weight and adult weight.
MEAT can be thought of as carcass quality, and its weight changes in carcass lean weight against changes in carcass fat weight.
WOOL rewards increased fleece weight with no regard to fibre diameter.
REPRODUCTION is a value related to greater numbers of lambs born.
SURVIVAL indicates the value associated with survival of these lambs.
DISEASE as is presently stands is an option used to rate animals for their ability to resist internal parasites based on faecal egg count.
Since SIL uses the same units for the sub-indexes as the overall index, you can readily see how much of a contribution a ram will make to your flock for the six different sub-indexes, or goal trait groups. Remember that a ram only passes on half his genetic merit to this progeny so the lambs they sire will on average preform to a level comparable to half the index or sub-index value.
This explanation is from Mark Young, Senior Adviser, SIL.