The health and productivity of cattle depends a lot on their genetics, and cattle genetics vary widely among herds and individual animals. Some cattle, for example, produce leaner beef, while other cattle gain weight faster. Deciding which cows or bulls to purchase can be difficult without knowing their genetic potential. Expected Progeny Differences (EPDs) are one tool that can be used to identify individual animals that possess superior genetics (Editor’s Note: Estimated Breeding Values [EBVs] are the sheep equivalent to EPDs for cattle).
EPDs quantify the relative genetic potential among cattle for various traits, such as birth weight, weaning weight, marbling, milk production, etc. EPD scores are assigned to individual animals in a breed. Cattle breed associations (e.g., American Angus Association, American Hereford Association, American Simmental Association, etc.) publish the EPDs which are calculated from performance records submitted by purebred cattle producers (i.e., people who raise cattle breeding stock for sale to commercial cattle producers). EPDs predict how the future offspring of a cow or bull are expected to perform relative to the offspring of other cows or bulls in the breed’s database. For example, a bull with an EPD for weaning weight of +25.0 is expected, on average, to produce calves that weigh 25 more pounds at weaning (i.e., at 205 days of age) than the progeny of the average bull in the breed’s database.
EPDs are reported as a plus or minus value in units consistent with the trait. For example, traits such as birth weight or weaning weight are expressed in pounds, hip height is reported in inches, and calving ease is expressed as the percentage of unassisted births. It is important to note that because an animal’s EPD values are relative to the other individual animals in each breed’s database, EPD values cannot be directly compared across breeds. That is, the EPD values from one Angus bull can be compared directly with the EPD values of another Angus bull, but neither can be compared directly with the EPDs of a Simmental or Charolais bull. However, EPDs can be compared across breeds by adding adjustment factors that are published annually by the USDA Agricultural Research Service. Each year scientists at the U.S. Meat Animal Research Center in Clay Center, Nebraska compare progeny of sires from 18 cattle breeds. The performance records of these progeny are used to calculate trait-specific adjustment factors for each breed. When the appropriate adjustment factor is added to an individual animal’s EPD score, the resulting value is known as an across-breed expected progeny difference (AB-EPD).
EPDs and AB-EPDs do not definitively predict cattle production outcomes. Breeding cows to a bull with a +40 weaning weight EPD, for example, does not guarantee that calves will weigh 40 pounds heavier at weaning. One reason is that cattle performance is affected by other factors in addition to genetic potential, such as nutrition, stress from weather or predators, or disease. Another reason is that EPDs for a given animal continually change as the database expands to include data from more offspring. This does not mean that the animal’s genetic makeup changes as the animal ages, rather the ability to predict the animal’s genetic influence improves as more information is incorporated into the EPD calculation.
The relative accuracy of EPDs can be assessed when comparing EPDs among animals. All published EPD values are accompanied by an accuracy score for each animal, expressed as a number between zero and one. Low accuracy values (closer to zero) indicate that the reported EPD is less reliable because it is based on fewer progeny. Higher accuracy values (closer to one) indicate that the reported EPD more likely represents the animal’s true genetic potential, and the EPD score is less likely to change as more progeny records accumulate.
EPDs can be used to identify cattle that will meet specific goals. For example, heifers (i.e., females that have not yet given birth to a calf) often have difficulty calving the first time, so it is usually a good idea to breed them with a bull that has a low birth weight EPD (i.e., the bull’s offspring tend to be smaller at birth than the breed average). Bulls with low birth weight EPDs also might be desired for breeding mature cows if limited human labor is available to assist cows having difficulty giving birth. Bulls with high weaning weight EPDs might be favored if the goal is to sell all calves at weaning, but milk production EPDs could also be important if some of the calves were to be retained to replace older cows culled from the herd. Where forage quality is poor, cattle performance will usually be optimized if bulls or cows with moderate EPDs for milk production are selected, but if plenty of high-quality forage is available, a high milk EPD is often desirable.
In summary, deciding which cattle to purchase can be difficult, exciting, and downright confusing at times. Remember that the “right” cattle for you will depend on your goals, marketing plans, labor, and forage resources. EPDS are a great tool to help identify cattle with the genetics that best match your specific situation. For assistance using EPDs for cattle selection, contact your local MSU county or reservation Extension office.