The DairyNZ subsidiary New Zealand Animal Evaluation Ltd (NZAEL) provides the Breeding Worth index (BW) for the purpose of ranking AB dairy sires according to the industry goal to “identify animals whose progeny will be the most efficient converters of feed into farmer profit”. 

NZAEL also controls the genetic base for the Animal Evaluation system.  The genetic base is the group of animals whose average evaluation is set to zero for all traits.  Estimates of genetic merit are reported against this base of zero.

The last update took place in 2008, when the Animal Evaluation system changed its base to a 1995-born cow. At that time, NZAEL also made the decision to comply with international conventions, which is to update the genetic base every five years. This year will see the Animal Evaluation system change its genetic base to the group of cows that were born in 2000 and that had performance records for all traits in the evaluation system in the dairy season 2002/03. 

The principal reason for updating the genetic base is to provide comparisons against a more familiar group of cows for current farmers than cows born in 1995.

In practice, farmers will notice lower reported Breeding Worth and most trait Breeding Values after the genetic base is updated, because the average cows born in 2000 are substantially genetically superior to the average cows born in 1995.