Border Dollar Index Structure
The overall value of ASBVs to clients is summarized in one score – the Border Leicester Dollar Index.
The Border Dollar Index combines the values of the rams traits, expressed as dollars of income per ewe joined to that ram each year.
The index is built up from the ram’s contribution to each extra kg of lamb grown by the First and Second-cross breeder, and each extra lamb weaned by the Second-cross breeder. It allows for the fact that only 50% of the growth and fertility of the First-cross progeny is attributable to the ram, and 25% of the growth of the Second-cross.
The Components of the Index are :
- WWT – weaning weight
- MWWT – maternal weaning weight (extra growth contributed by the ewe = milk)
- PWWT – post-weaning weight (approx 9 months of age)
- YGFW – yearling greasy fleece weight
- NLW – number of lambs weaned
- PFAT – fat-depth at post-weaning
- PEMD – eye-muscle depth at post-weaning.
Extra Dollar Returns
Every 5 index points above the breed average is estimated to return a extra $1,000 over the 4 years working life of a ram.
The second-cross breeder receives the benefit of the higher fertility (NLW) and milking ability (MWWT) whilst both First and Second-cross breeders share the benefit of the higher weaning weight (WWT) and Post-weaning weight (PWWT).
Changing Index Structure
The index structure is enhanced periodically to more accurately reflect value of traits to the lamb industry.
Further enhancements in ASBVs and Index structure may be anticipated in the future as geneticists improve their methods of calculating traits and assessing heritability.