How are selection indexes calculated?

The selection indexes published within TransTasman Angus Cattle Evaluation are economic selection indexes and are derived using BreedObject software, as developed by the Animal Genetics & Breeding Unit (AGBU) in Armidale, NSW.

A range of different selection indexes are published, with each individual selection index reflecting differences in net profitability, being income minus expenses, in a defined breeding system, target market and production system.

For the breeding system, target market and production system relevant to each respective selection index, the BreedObject software firstly calculates the net economic value of changing each trait in the breeding objective by one unit, independent of any change in other traits. The BreedObject software then links the economic value of the traits in the breeding objective with the Estimated Breeding Value (EBV) traits published in the TransTasman Angus Cattle Evaluation, and places appropriate emphasis on each EBV based on its relative economic importance in the defined breeding system, target market and production system.

Importantly, the trait emphasis that is placed on each EBV is determined by science, not the breeding preferences of either individual breeders, researchers, or staff at Angus Australia.