By Lance Bauer, Director of Breed Improvement & Western Field Representative
As discussed in the previous article EPDs are Expected Progeny Differences, and the calculation of EPDs was discussed. In order to effectively use EPDs as a tool you must understand how to use them correctly, you wouldn’t use a screw driver instead of a hammer to put in a nail. EPDs are to be used as a tool to compare animals to each other or to compare against an average. EPDs are an estimate, based on pedigree and performance, of how an animal’s progeny should perform on average when compared to the progeny of another animal or against a breed average. They offer a quick and efficient way to compare how an animal’s progeny should perform because of genetics. They are not the only tool that you need to use in cattle evaluation, but they are very useful. You wouldn’t build a house just using one tool, but many different tools are required to build a sturdy functional house.
EPDs can help improve traits that are measured and of economic relevance to a producer. They can be used as a tool in selecting both bulls and females for production. When deciding between two or more animals the way to compare is to simply take the difference between the two in order to find the expected average difference between the animals’ progeny for the trait that is being selected for. With this in mind it is important to make sure that you do put all of your emphasis on a single trait and fall into single trait selecting. Single trait selection can lead to issues in the future because most of the traits that are measured have a genetic correlation to other traits. If you select on the single trait of low birth weight, then many times you will bring the other growth traits down, that is not to say that there are not animals that have low birth weight and have large weaning and yearling weights.
When looking at EPDs the top line is the EPD and the line below that is the accuracy value. Accuracy values range from 0.0 to 1.0 with an accuracy of 1.0 never being attained. Accuracies will increase as more records are reported on an animal, and if an animal has genomic data. Even with lower accuracies EPDs are still the best genetic tool that is available, they are better than actual weights, adjusted weights and ratios. It is like using a hand saw vs a power saw to cut a board, both methods are better than using a tool that isn’t built for the job.
Now that you know how to use EPDs here is a simple example using two bulls, Bull A and Bull B, and in your visual appraisal both of these bulls are sound functional animals that you can use. In your operation you are trying to increase your weight traits and your carcass traits and this bull will be bred to mature cows. When you are selecting the bull you will be looking at Weaning Weight, Yearling Weight, REA, and MARB. If you focused just on one you would be single trait selecting and could lead to issues down the road. Looking at the Weaning weight of the bulls Bull A has a WW EPD of 42.0 and Bull B has a WW EPD of 50.0, with this information we expect Bull B’s calves to be 8 pounds heavier on average at weaning. The next trait is Yearling Weight and Bull A has a YW EPD of 65.0 and Bull B’s YW EPD is 82.0, so we would expect Bull B’s calves to be 17 pounds heavier on average at yearling weight. Looking at REA next Bull A has a REA EPD of 1.02 and Bull B has a REA EPD of 1.12, meaning that Bull B’s calves should have .10 in2 more REA on average than Bull A’s calves. Now for the final trait in this selection, MARB Bull A has an IMF EPD of 0.25 and Bull B has an MARB EPD of 0.05, meaning that Bull A’s calves should average 0.20 percent more IMF than Bull B’s calves. In this scenario looking at all of the traits used it would be my choice to use Bull B.
In order to properly use EPDs you need to determine the needs of your operation and what traits need improving, while making sure that you do not single trait select. It is also important to remember that cow EPDs matter, as well as bull EPDs. EPDs are the best genetic tool that we have for selection and should be used as a tool with the purpose of genetic improvement as the goal. They are one of several tools that are used in selecting cattle, if selecting cattle is compared to building a house, it is very difficult to build a house with just one tool, the same can be said about making breeding decisions in cattle. The next article in this series will be a guest article about how genomics factor into EPDs and GE-EPDs, by John Genho, and the next will be about using indexes by Dr. Matt Spangler.