Expected Progeny Difference, or EPD, is the prediction of how future progeny of each animal is expected to perform relative to the progeny of other animals within the same breed. The EPD is calculated using information submitted to the breed association. This information includes pedigree, actual performance data (weights) of the individual, performance information submitted on the individual animal’s relatives and offspring, and genomic information collected from DNA analysis.
How are EPDs expressed?
EPDs are expressed in units of measurement for the trait they represent, such as pounds, days, inches, etc. EPD values can be positive or negative. It is important to note that negative values may be preferable in some situations. For example, positive/higher EPD values are generally considered good for weaning weight, while a negative/lower EPD value is typically desired for birth weight, if you are selecting a bull to use on heifers.
How accurate are EPDs?
EPDs change over time as more information is submitted on an individual. How much an EPD can change is determined by the accuracy of the EPD. Accuracy is just that – how accurate or reliable an EPD is. It is measured on a scale from 0 to 1, where the higher the number means the greater the accuracy and the less that EPD value will change over time.
How are EPDs generated?
EPDs are generated using statistical models that remove environmental influences and other factors such as management systems, gender and age. However, animal performance ultimately relies on both genetic and environmental factors. An animal with EPDs for a certain level of performance may or may not live up to its genetic potential if its environment is sub-standard.
What about breed indexes?
Another term that you will see associated with EPDs are indexes. Unlike EPDs that focus on a single trait, indexes combine EPDs for several traits into a single economic value which can be used to make selection decisions. Indexes are expressed in dollars per head, and higher index values mean a higher dollar value per head. An index value only has meaning when it is compared to the index value of another animal of the same breed.