Sire evaluation in the beef industry has become a sophisticated procedure developed through experience, research, improved statistical procedures and the development of high-speed computers. Fortunately, a beef producer only needs to know a few basic concepts to interpret and use the results. The EPD is reported as a plus or minus value in the unit in which the trait is measured, such as pounds for birth weight. An example of the Angus Sire Summary, which is similar to those of other breeds, is shown in Table 1. On the other hand, a bull with an EPD of -2.7 pounds for weaning weight would be expected to produce calves 2.7 pounds lighter at weaning weight than the average bull of that breed.
Some breed associations express EPDs as ratios.
When ratios are used, conversion factors are given so the ratios can be translated to EPD values. For example, the 1985 Simmental Sire Summary indicates that a one unit change in weaning weight ratio is equivalent to 5.27 pounds. EPDs are calculated from a sire's progeny data. All bulls listed in the sire summary can be directly compared using EPD values. EPDs are an estimate of how a bull's progeny would be expected to perform compared to any other bull listed in the same summary.