Interpreting the Sire Summary - CCA Breed Improvement

Accuracy of EPDs
Accuracy values give us an indication of how close our estimates are to an animal’s true genetic value. Accuracy
values are extremely useful to breeders in determining the reliability of an EPD. An accuracy value can range from
0.0 to 1.0, depending on the amount of
Bull A
ACC = 0.40
Possible Change
± 17.7 lbs
Bull B
ACC = 0.80
Possible Change
± 6.4 lbs
information that is known about an animal
for any one of the reported traits. As the
amount of information included in the
analysis of a trait for an individual
increases, the accuracy value for that trait
increases accordingly.
0 5 10 15 20 25 30 35 40
The table below (Possible Change Values
for the North American Charolais
Evaluation (Growth Traits) and the Total
Genetic Evaluation (Carcass Traits)) shows
the possible change (standard error of
prediction) at various levels of accuracy for
the traits reported. As the accuracy level
Ylg Wt EPD (pounds)
increases, the possible change value
decreases. An EPD can change from year
to year even though it may have a high
level of accuracy. The point to remember is that the expected change of an EPD with a high ACC is
correspondingly less than those EPD with a lower ACC value. The possible change of a specific EPD, given
different levels of accuracy, can be seen in the diagram above. Two bulls have a Yearling Weight EPD of +20.0 but
different ACC values. The figure illustrates the possible range where the true genetic value is. Bull A has an ACC
of .40 with a possible change of 17.7 pounds, and bull B has an ACC of .80 with a possible change value of 6.4
pounds. As additional information is reported and accuracy levels increase, we would expect the EPD to stay within
range of the possible change value.
Even though both bulls have an EPD of +20 pounds for yearling weight, Bull B has a higher reliability that his true
genetic value is in the narrower range of 13.6 to 26.4 (20 ± 6.4).
The accuracy (ACC) of a given EPD can help determine the amount of risk a breeder is willing to take in their
breeding decisions. Which bull is more desirable? The bull with the high accuracy is more predictable, but the
amount of genetic change that can be made is correspondingly limited as well. Bull A has the same Yearling
Weight EPD, but his true genetic value may be beyond that of Bull B. Therefore Bull A could possibly increase the
amount of genetic progress made, but he is also more of a risk because his true genetic value falls within a wider
range.
The following table (Possible Change Values) gives the possible change or variation (either plus or minus) that is
possible for each EPD with a given accuracy for the traits evaluated in the North American and the TGE analyses.
Approximately ninety-five (95) percent of the time the EPD will not deviate outside of these parameters.