For several years, geneticists at the U.S. Meat Animal Research Center (USMARC) have provided the table of adjustment factors to be used to estimate across-breed expected progeny differences (AB-EPDs). These adjustments are based on comparative breed research conducted at the USMARC. Adjustment factors for a few selected breeds are presented below.
To calculate across breed EPDs, add the adjustment factor found in the table to the within-breed EPD published in the most recent genetic evaluation for the animals of interest. As an example, assume a Simmental bull and a Charolais bull are being compared for use as as a terminal sire on mature Angus-based cows. The Simmental bull has a within-breed YW EPD of +60 and the Charolais bull has a YW EPD of +35. To fairly compare the YW EPDs of these two bulls of different breeds, the EPDs must first be adjusted to a common base using the across-breed table. Using the table, the Simmental bull would have an across-breed YW EPD of +84.5 (60 + 24.5 = 84.5) and the Charolais bull an across-breed YW EPD of +83.9 (35 + 48.9 = 83.9). Comparison of the calculated across-breed EPDs for these two bulls suggests they would transmit similar genetics for yearling growth as the difference in their across-breed YW EPDs is minimal.
It is important to note that the adjustment factors found in the table do not represent a direct comparison of breed differences. Without across-breed adjustment factors, EPDs for animals of different breeds cannot be accurately compared. The across-breed adjustment factors take into account breed differences, as well as differences in the established base year (year in which average EPD in breed equals zero) used in the calculation of EPDs for each breed. For these reasons, the adjustment factors themselves are not reflective of breed differences. The adjustment factors should only be applied to the most current EPDs available from the breed associations.
Source: Dr. Scott P. Greiner, Extension Animal Scientist, VA Tech.