A GENOMICS BULL BUYING GUIDE A COMMERCIAL PRODUCER’S GUIDE TO SELECTING BULLS

by Jamie T. Courter, PhD, Bovine Technical Services Manager, Neogen Genomics for the American Simmental Association

As you continue to flip through various catalogs, selecting bulls as you have so many times before, I would like to take this opportunity to provide what I believe are fundamental pieces of information to better assist a producer in their bull buying decisions. In addition to the overall soundness and conformation of a bull, it is always important to select a sire that is backed by data. You wouldn’t necessarily go out and buy a new pickup truck without researching its horsepower, torque, and tow-rating. Instead, you would ensure that the overall mechanics of the engine matched your daily needs. The same should be true about purchasing a new herd bull or AI sire. Instead of an owner’s manual, you now have expected progeny differences (EPD).

What is an expected progeny difference (EPD) and how is it interpreted?

In addition to photographs, most catalogs include a multitude of information and numbers for a given sire. While they can be overwhelming, those numbers summarize what is currently known about the genetic potential of an animal. These values are referred to as expected progeny differences (EPD) and represent an estimate of the genetic merit an animal will pass on to its offspring.

Seedstock producers invest heavily into reporting the key information used to calculate an EPD. For traditional EPD, these include individual pedigrees, phenotypes for key traits of interest, genomics, and progeny information, once available (Figure 1). When an EPD is reported back to the seedstock producer, the estimate of genetic merit is summarized in four different ways:

1) Expected Progeny Difference (EPD): The first number listed following the trait abbreviation, an EPD is an estimate of the average genetic merit an animal will pass on to its progeny. They can be used to rank animals according to their potential to make genetic change within a herd, or when making bull buying decisions. For example, if you are comparing a bull whose weaning weight EPD is +53 to another whose EPD is +63, one would expect the second bull’s progeny to weigh on average ten pounds more than the first bull’s. Therefore, if the second bull is purchased and sires 30 progeny in a season, all other factors excluded, that should be

300 extra pounds of weaning weight expected from the second animal as compared to the first.

2) Percentile Rank: A percentile rank reports where the specific EPD for that animal ranks across the entire breed. Ranging from 1 to 100, if an individual is in the top 1 percent, they are one of the best animals in the database for that trait of interest. Percentile rankings are particularly useful to gain bearings as to what a “good” or “bad” EPD looks like within a breed population. Percentile rankings quickly tell the producer if the animal is above average (less than 50 percentile rank) for a trait compared to all other animals in that population. It is important to know which other animals are compared in the percentile rankings. For instance, only purebred Simmental cattle are compared to other purebred Simmental cattle in the percentile ranking, but not compared to Simbrah, Fullblood Fleckvieh or hybrid cattle in the ASA database.

3) Accuracy: Ranging from 0 to 1, accuracy is an estimate of the confidence that the EPD provided is the “true EPD” of the animal. After all, an EPD is a geneticist’s best estimate of genetic potential on an animal given the information provided to the evaluation at that time. As more progeny records and phenotypes on an animal are reported, geneticists know more about that animal. This results in the EPD fluctuating up and down over time, while the accuracy increases.

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