Putting EPDs to the Test   (Gelbvieh World, December, 1998)

By Tom Brink, AGA Executive Director

Suppose you wanted to show your neighbor that EPDs can be used effectively in small herds. To prove this point, you plan to breed a group of yearling Gelbvieh heifers to one HIGH birth weight EPD sire and one LOW birth weight EPD sire. The objective of your experiment is to breed enough heifers to produce 10 bull calves from each sire. You will then show him the birth weight difference between the two sire groups. Two proven Gelbvieh A.I. sires are chosen for your experiment: Mr. 709R "Doc" as the high birth weight sire (+4.5 BW EPD) Mr. Sensation 506S as the low birth weight sire (-3.8 BW EPD).

You could find the needed heifers, breed them, and wait nearly a year for the results. Or, you could utilize the AGA database and simulate the experiment using actual data from hundreds of heifers that had calves in the past by these sires. AGA has birth weight records on 253 first-calf heifers that produced Doc-sired bull calves. The database also contains 554 heifers that had bull calves sired by Mr. Sensation.

It's much faster and less expensive to use the AGA database, so you decide to go that route. Your neighbor agrees that randomly selecting 10 bull calves from each sire's data pool will prove (or disprove) the usefulness of EPDs in small groups of cattle. The selections must be made randomly from within the available birth weight data. However, with this condition met, results of this "virtual experiment" should reflect what would happen if the test was actually conducted on a group of Gelbvieh heifers.

Results Show Large Birth Weight Difference

The accompanying table shows actual birth weights on 20 bull calves (10 from each sire) that were randomly selected from available AGA data. As expected, most of the birth weight difference between the sire groups was caused by sire genetics. Dams of these bull calves had very similar BW EPDs on average. And remember, all of these bull calves were born to first calf-heifers, so calving difficulty would be expected to accompany the heavier birth weights.

Randomly Selected Bull Calf Birth Weights* (lbs.)

Averages:

*All calves were born to first calf-heifers.

As it turns out, there was a 12 pound difference in birth weight between the two sire groups. This is somewhat larger than expected, given the difference in the two sires' BW EPDs (8.3 pounds). Keep in mind, however, that the small sample size (10 head per sire) provides limited opportunity for precise genetic expression.

Most importantly, your neighbor is now convinced that EPDs do work. After seeing the results of this experiment, it is clear to him that Doc, on average, sires significantly heavier calves than Mr. Sensation, just as their BW EPDs predicted. Birth weights are highly variable, because they are subject to many non-genetic influences (such as weather, plane of nutrition, etc...). Even so, EPDs are good predictors of group performance, even within fairly small groups of cattle. Your neighbor has now seen this first hand. The virtual experiment was a real success. And it sure was a lot easier calving those heifers on paper!