An expected progeny difference (EPD) is the relative difference in performance expected in future progeny of an individual, compared with the future progeny of another individual. An EPD describes the average merit of a gamete produced by an individual (sperm or egg) for a particular trait, e.g., birth weight, weaning weight, marbling score. EPDs are used to describe the portion of genetic merit that is transmitted from parent to offspring. Each EPD is reported in the units of measure for that specific trait. EPDs are derived from multiple sources of information, including pedigree relationships, an animal's own performance record, and progeny performance records. An animal's progeny performance is the most valuable source of information for computing EPDs. EPDs are reported for beef cattle and are equal to one-half the estimated breeding value obtained from progeny test records.
EPDs are statistical estimates of genetic merit that producers should use when making selection decisions. EPDs are preferred over an actual performance record of an animal or a ratio for use in selection decisions as the EPD eliminates variation across herds due to environment. EPDs have been shown to be seven to nine times more effective in generating selection response than performance records or ratios.
EPDs are produced by either breed associations or universities during each respective breed's National Cattle Evaluation (NCE). In a NCE, all eligible performance records are used to compute EPDs on all animals simultaneously. Most breeds conduct NCE twice per year, and EPDs are released via Web sites and updated performance pedigrees. It is important that producers obtain and use the most current EPD values as EPDs routinely change due to the inclusion of new data in the evaluation. A common misconception is that changes in EPDs are caused by inaccuracy in the evaluation or model. Changes should be viewed favorably as they are the result of inclusion of more information in the evaluation.
