NZAEL are responsible for sire BW and determining the traits included. If an update is made to sire BW, the same update is applied to cow BW.
A cow’s BW is based on ancestry, individual and offspring records. A bull’s BW is based solely on ancestry information, until it has daughters with records. BW incorporates eight breeding value (BV) traits – traits that have been recognised as having the greatest impact on farmer profitability. It is comparable across all herds, ages and breeds.
A cow with a BW of 110 indicates the cow is expected to breed daughters that are $55 more profitable, per year, per unit of feed, than daughters of a cow with a BW of 0.
Information that contributes to evaluating a cow’s worth
A cow’s BVs takes into account three types of records:
- Ancestry (all female relatives related through ancestry such as sisters and nieces) – used when she’s a calf.
- Own performance (once she is milking).
- Performance of offspring (or direct descendants) – included once she has herd-tested daughters.
An untested cow is evaluated solely on its ancestry records. As the number of lactations and herd tests increases, her own performance starts contributing to her BW estimate, although ancestry still plays a dominant role. The true indicator of a cows' ability to generate profitable replacements is through the performance of her progeny (daughters or daughters of sons).
The diagram below shows the weightings for a cow’s BVs at different stages of her herd life. The increased weighting on progeny information reinforces the definition of BW.
Ancestry/own lactation/progeny information weighting in cow BV
To calculate the BW of a cow, multiply its BVs by the EVs and add together. Cow BVs are shown on a MINDA Trait Evaluations report.
Find out more about Breeding Worth on the DairyNZ website.