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Additive Adjustment Factors to Estimate Across-Breed EPD

Researchers at the Roman L. Hruska U.S. Meat Animal Research Center (MARC) in Clay Center, Neb., develop breed adjustment factors annually so that expected progeny difference (EPD) values can be compared across breeds. This process allows the estimation of across-breed EPDs, sometimes referred to as AB-EPDs. The across-breed EPD concept was introduced in the late 1980's and continues to spark interest with commercial bull buyers using more than one breed of bull. This is mostly due to the fact that without adjustments, the within-breed EPDs cannot be used to directly compare animals of different breeds, since the values are typically computed separately for each breed.

Table 1 presents the most recent MARC adjustment factors that can be added to the EPDs of animals of different breeds, adjusting their EPD values to an Angus equivalent. The adjustment factors, given relative to an Angus equivalent of zero for each trait, take into account breed differences measured in the Germplasm Evaluation Project at MARC, as well as differences in breed average EPDs and base year. Animals of various breeds can be compared on the same EPD scale, after adding the specific adjustment factor to EPDs produced in the most recent genetic evaluations of the representative breeds. Use of these factors does not change differences in EPDs among bulls within a breed. However, it does affect differences among bulls of different breeds. The example below illustrates EPDs for Angus and Simmental bulls after across-breed adjustment factors have been applied to estimate AB-EPDs. The AB-EPDs for Simmental Bull #002 are on an Angus-equivalent scale and can be directly compared with values for Angus Bull #001.

It is important to remember that EPDs are not perfect when comparing bulls even within a breed; therefore, AB-EPDs are somewhat less accurate when comparing animals of different breeds. AB-EPDs are most effective for selecting bulls of two or more breeds for use in systematic crossbreeding. When evaluating the potential application of AB-EPDs as a tool for a particular breeding program, commercial cow-calf producers must first examine the needs of their individual operations. Producers must diligently review their breed choices and crossbreeding systems in order to provide the best sire selection match to cow genetic type, environment, feed resources, and market targets.

With the release of the new Angus NCE, the across-breed adjustment tables from 2016 no longer apply. The USDA will be re-estimating the across-breed adjustment factors based on the new evaluation. When these new adjustments are available, they will be updated here.

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