While some are decking the halls, others are getting ready for another season. This season has no mistletoe or tinsel but it can be just as merry: Bull Sale Season! As it approaches many will start to filter through sale catalogs and try to identify sires that are the best fit for their cattle herd. This is challenging. Producers must predict which genetic traits will be most marketable in two production cycles when the calves from these sires will be marketed.
In general most expected progeny differences (EPD’s) are well understood within the industry, however some are overlooked. While single trait selection should be avoided, determining areas within your herd which warrant genetic improvement can give producers direction when purchasing bulls. In determining the exact definition of EPD’s one should either consult the associated breed association, as EPD’s are breed specific, or often seedstock producers will include definitions within the catalog.
When looking at EPD’s it is good to understand the heritability of the traits which you are selecting for. The heritability of a trait defines the likeliness that trait will be passed to offspring. It is the measure of degree (0-100%) that the offspring will resemble the parent for a specific trait. A general rule of thumb is that the farther the trait is from the end point (carcass) the less heritable it will be. Reproductive traits tend to be lowest in heritability (typically less than 20%), growth traits tend to be moderately heritable (20% to 40%), and carcass traits are highly heritable (greater than 40%). An understanding of the heritability of desired traits will allow one to optimize the selection of traits which are desired and avoid the inclusion of less desirable traits.
All EPD’s are reported with an accuracy number. A common misconception is that accuracy describes the variance expected within a calf crop, when in fact accuracy can be defined as the relationship between the estimated EPD of the animal and the “true” EPD of the animal. It is expressed numerically from zero to one. The closer to one the accuracy is the more reliable the EPD. This is a function of the amount of information available to calculate that is given trait, so as the volume of records used to estimate EPD’s increase, so will the accuracy. It is normal for young bulls to have lower accuracy of their EPD’s, as there is not as much data to support them.