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.