By definition EBVs are an estimate. That is; they are Estimated Breeding Values. For this reason an accuracy value is presented with every EBV and gives an indication of the amount of information that has been used in the calculation of that EBV. The higher the accuracy the lower the likelihood of change in the animal’s EBV as more information is analysed for that animal or it’s relatives. The following guide is given for interpreting accuracy:
less than 50% EBVs are preliminary and could change substantially as more performance information becomes available.
50-74% medium accuracy, usually based on the animal’s own records and pedigree. Most sale animals have EBVs in this range.
75-90% medium-high accuracy. Some progeny information included. It is unlikely that EBVs will change much with addition of more progeny data.
more than 90% high accuracy estimate of the animal’s true breeding value.
As a rule, animals should be compared on EBVs regardless of accuracy. However, where two animals have similar EBVs the one with higher accuracy could be the safer choice, assuming other factors are equal. Implications for bull buying Most bulls presented for sale have EBVs with an accuracy of less than 75%. At this level of accuracy the EBVs may change as more data becomes available in subsequent analyses. Some buyers will argue that because of this the EBV are of little value. This is not so. A low/medium accuracy EBV is still the best available estimate of genetic merit based on the performance of the animal and all recorded relatives.
Buyers who regularly buy bulls around their desired EBV level will inherit that level of performance into their herds quite accurately over a number of bulls. This is because there is an equal opportunity for the EBV to move up or down, which creates an averaging effect over a number of bulls. It is estimated that a buyer who purchases about 10 young (lower accuracy) bulls at their desired EBV level will inherit that level of performance with an effective accuracy level of around 90%. When buying young bulls with lower accuracy EBVs it is recommended that initially little emphasis is placed on the accuracy of the EBV. It is only when a number of bulls are considered equally acceptable that I would use the accuracy to help reach a decision.
You can also interpret accuracy as a measure of risk. If you are only selecting one sire to join with heifers accuracy would be more important than say buying several sale bulls for a multiple sire joining group. Breeders wanting to further discuss the role of accuracy in selecting bulls are invited to contact Christian Duff on (07) 4927 6066.