Bull buyers should view the numbers attached to a herd sire’s pedigree as valuable information about how that animal could reshape their operation.
Expected progeny differences (EPD) represent the genetic component of an animal’s phenotype that are expected to be passed on to the next generation.
The numbers can be valuable for producers looking to improve calving ease, increase calf weights or incorporate other important economic traits in their herds, said geneticists Alison Van Eenennaam and Matt Spangler.
“EPDs are the best estimate we have of how a bull’s or cow’s future progeny will perform, on average, compared to another bull or cow, or the breed average of a given trait,” Van Eenennaam said during a Jan. 18 webinar sponsored by the National Cattlemen’s Beef Association. She is a genetics extension specialist with the University of California, Davis.
An animal’s own performance is combined and properly weighted — along with the performance of relatives like progeny, parents, grandparents, full and half siblings and all genetic relationships — to generate an EPD.
EPDs cover classes of traits that deal with information like weights, calving ease, maternal characteristics, carcass quality, stay ability (how long it will remain in the herd), docility and maintenance.
Numbers are associated with each of the traits.
For example, if a bull has a 10 for calving ease compared to a bull with a six, the higher number means there will be more unassisted births.
Sometimes people focus on the birthweight number but that is not correct, said Van Eenennaam.
“The important trait is whether or not the calving proceeds unassisted. While birthweight is an indicator of calving ease, it really doesn’t tell the whole story. Calving ease is really the relevant economic trait,” she said.
Trait selection is nuanced depending on genetics, environment and breeding goals.
A bigger EPD number is not always better. It depends on the trait and the needs of the ranch. A producer may not want more milk production or taller cattle because of individual ranch conditions.
An animal’s numbers can change over time.
“As a sire begins to have a lot of offspring, we actually learn about the genetic merit of that sire,” said Spangler, the extension beef genetics specialist at the University of Nebraska.
“There is a fair degree of potential change associated in low accuracy young bulls. You may be unfairly penalizing a bull that really may be suited to a production system,” he said.
“As a sire begins to have a lot of offspring, we actually learn about the genetic merit of that sire.”
The correlation between traits should also be considered. Growth and feed intake records have a genetic correlation, for instance.
“Many traits have at least some genetic correlation between them. Think about the relationship between early growth rates and their relationship to yearling weights,” he said.
Economically relevant traits are those that are directly associated with either a cost or a source of revenue.
A high weaning weight is a source of revenue but it is also a source of cost. Cows with greater genetic potential for lactation to feed a big calf also eat more even when they are dry.
“Caution should be used when choosing bulls to produce daughters, particularly in limited feed environments,” he said.
“The cows that were more conservative in their lactation were more economically efficient,” he said.
Accuracy in these statistics is important.
Bulls with higher EPD accuracy will have more uniform groups of calves.
“Accuracy is not the same thing as precision. Accuracy of a bull’s EPD does not tell us anything about how uniform his offspring group is going to be. Accuracy gives us a measure of how closely related the EPDs or prediction or prediction of their genetic merit is to their true progeny difference,” he said.
When a mating is carried out, the bull passes on a random half of his genetics to the next generation. There are differences in what offspring receives and that creates variation in the progeny.
Animals may be flush mates and would be assumed to be the same but genotyping can show a difference in traits. The bull may pass on unfavourable traits to one calf but the next one may receive desirable qualities. That creates differences in the offspring.
“If all offspring were the same, we wouldn’t be able to make any kind of genetic change,” he said.
Genetic fact sheets for cattle breeders may be viewed at ebeef.org/