EBVs are expressed as the difference between an individual animal’s genetics and the genetic base to which the animal is compared. The “genetic base” can roughly be described as the historical genetic level of that particular breed. For most breeds, their genetic base will have been set in the mid 1990’s. Importantly, the genetic base for each breed will be different, so only EBVs for animals within a particular analysis can be directly compared.
Compare with the current breed average
As most breeds have experienced significant changes in their genetic merit for most traits since the mid 1990’s (ie. their genetic base), the first step when interpreting an EBV should be to compare it to the current breed average EBVs for the breed. This will give you an indication of how the animal compares with the current genetic level for the breed for each trait.
A set of breed average EBVs should be enclosed in all BREEDPLAN reports and sale catalogues, as well as through your breed's EBV Enquiry.
Compare with the Percentile Bands Table
Comparison with the breed average EBVs allows you to establish whether an animal is above or below the current genetic level of the breed. This can be taken further by comparing the animal’s EBVs to the Percentile Bands Table to assess exactly where the animal ranks within the breed for each trait.
As with the breed average EBVs, a Percentile Bands Table should be enclosed in all BREEDPLAN reports and sale catalogues, as well as through your breed's EBV Enquiry.
Comparing projected performance
Comparing the EBVs of two sires to estimate the difference in expected performance can help with decision making.
To demonstrate this, let’s say the first bull has a 600 day weight EBV of +41, while the second bull has a 600 day weight EBV of +21. Comparing these animals shows a difference in 600 day weight EBV of 20 kg. As on average half of this difference will be passed on to the progeny of each sire, it can be estimated that calves from the first bull would be on average, 10 kg heavier than those from the second bull at 600 days. Extending this to a single year’s drop of 50 calves, this difference equates to a potential production difference of 500 kg in live weight by the time the calves reach 600 days of age.
It is important to note that in the above example we are assuming both bulls are used over dams of similar genetic value/breed and their progeny are run under similar conditions.
By definition, an EBV is an estimate of an animal’s true breeding value. To provide breeders with a measure of the reliability of the estimate, BREEDPLAN produces an “accuracy” figure with each EBV. The “accuracy” provides a measure of the stability of the 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, its progeny or its relatives.
Although the accuracy of an EBV should be considered, animals should be compared on EBVs regardless of accuracy. Where two animals have the same EBV however, the animal with the higher accuracy would normally be used more heavily than the bull with the lower accuracy because the results can be predicted with more confidence.
Although EBVs provide an estimate of an animal’s genetic merit for a wide range of traits, they do not provide information for all the traits that must be considered during the selection of functional cattle. In all situations, EBVs should be used in conjunction with visual assessment for other traits of importance (eg. structural soundness).