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Spangler: Bull sale catalogs provide abundant information that may be confusing

by Wyoming Livestock Roundup

With bull buying season rapidly approaching, ranchers are starting to think about what bulls they will purchase in the coming year and how these bulls can improve their herd. 

“Genetics come to the forefront of people’s minds because they need to go out and purchase a bull, but really, determining what the rancher need in a bull is a year-long process,” according to University of Nebraska Beef Geneticist Matt Spangler. 

Ranchers should evaluate what changes they want to make in their long-term breeding objectives and marketing philosophies, and then evaluate where they stand with past calf crops to determine what type of bull they need to purchase to meet those objectives. 

Then producers can start the confusing process of analyzing sale and AI catalogs to find the right bull. 

“There’s actual and adjusted records, ratios, EPDs, economic indexes and genomic information,” Spangler said. “How does each producer determine what is important?”

Identifying differences

Spangler encourages producers to focus on the things that allow them to see the differences in bulls in terms of different sires. 

On a genetic level, producers should evaluate the EPDs or the bio-economic index values, if they have them. He steers buyers away from looking solely at phenotype. 

“Phenotype, or what we see, is equal to the genetics of the animal and the environmental influences, like management,” he explained.

By selecting solely for phenotype, ranchers could be making a grave error because environment and management aren’t heritable traits. 

“Producers simply can’t compare phenotypes,” Spangler stated. “Instead, focus on the genetic merit of that animal as a parent.”

Raw data

Raw data, such as actual birth, weaning and yearling weights and ribeye area from ultrasound, are influenced by a number of factors, including management, nutrition, differences in age of the animal, sex, age of dam, climate and genetics. 

In order to compare apples to apples, Spangler said this information has to be adjusted to form a contemporary group of animals. 

“If the producer pulls a bull out of this group to show it, and they feed it a higher plane of nutrition, he no longer fits with his contemporary group,” Spangler said. 

By adjusting this data for sex, age and age of dam, a ratio is developed for the group, which allows producers to compare the animals within a contemporary group. 

The downside of this is these ratios only allow comparison of animals within the contemporary group. Another group may have a different set of environmental influences, so the averages may not be equal. 

“I think it has little value in selecting the next herd sire because of the different environmental influences and the different herd averages,” Spangler explained.


“To separate the wheat from the chaff, I would encourage people to evaluate the EPDs,” the geneticist continued. 

Expected progeny differences, or EPDs, include pedigree information from the parental and collateral relatives, the individual’s own records and progeny information. EPDs can be used across herds but only within a breed. 

“Offspring of one sire can exhibit more than three-fourths diversity of the entire population,” Spangler said. “What some people don’t understand is the variation within the progeny from a single sire. Just because two animals are out of the same sire doesn’t make them identical. Actually, they can be quite diverse because the sire contribution to genetic variation is actually one-fourth.”

As the sire has more progeny, his accuracy rate will increase because more is known about the type of offspring he will produce. 


Some ranchers make the mistake of purchasing bulls that are half siblings, thinking they can increase the consistency in their calf crop, Spangler said. 

“This is a flawed strategy because only 25 percent  of variation can be controlled through the sire. If producers really want to improve their consistency, they would be better off to look for a group of bulls with the same weaning weight EPD, instead of buying half brothers,” he noted.

A calf will have a pedigree index EPD, which is made up of half the sire’s and half the dam’s EPDs. Until the calf starts siring offspring of its own, Spangler said its accuracy will be low. 

“EPDs are only an estimate. The accuracy tells us how close the estimate is to the true value,” Spangler explained. 

“Accuracy is not a measure of progeny variability, but it is a measure of how much an EPD could change. It is a way of quantifying data, and accuracy increases with additional data,” he added. “A low accuracy bull is not more likely to have more variable offspring than a highly accurate bull.” 

Gayle Smith is a correspondent for the Wyoming Livestock Roundup. Send comments on this article to

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