Expected progeny differences: Behind the scenes
While some have been 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.
Performance Ratios and Contemporary Groups are often used by seedstock producers. This evaluates the individual performance of a bull within a group that have been managed the same. The average performance ratio for a contemporary group is 100, the differences in performance is the percent the animal is higher or lower than the group. For example: a bull with a performance ratio of 114 performed 14% above the contemporary group in the measured traits. While this allows producers to evaluate the bulls from within a contemporary group, it does not compare them to others within the industry. In addition, if lower preforming bulls are culled from the group this will bias the comparisons. One should consider the size of the group, with larger groups being desired.
Overall, producers should have short and long term goals for the genetic progression of their herd. These goals should include the focus and direction of their marketing plan, if replacement heifers will be retained or purchased, and cross breeding considerations, as a truncated list. Having a plan, and sticking to it while keeping production goals in mind when selecting bulls will help optimize success, and remember never drink eggnog when buying bulls.