by Larry Kuehn and Mark Thallman
Across-Breed EPD (ABEPD) Adjustment Factors: National Cattle Evaluation (NCE), and the
resulting Expected Progeny Differences (EPDs), have resulted in substantial genetic change
since their inception in the 1970s. However, EPDs are generally only comparable within breed
because of differences in the genetic base. Since 1993, the U.S. Meat Animal Research Center
(USMARC) has produced a table of factors to adjust the EPDs of cattle so that the merit of
individuals can be compared across breeds. Adjustment factors for carcass traits have been
calculated since 2009 and carcass weight was added in 2015; to be included, breeds must have
carcass data in the U.S. Meat Animal Research Center (USMARC) database and report their
carcass EPDs on an actual carcass basis using an age-adjusted endpoint.
Bulls of different breeds can be compared on the same EPD scale by adding the appropriate
adjustment factor to the EPDs produced in the most recent genetic evaluations for each of the
eighteen breeds. Normally, the EPDs of animals from different breeds cannot be compared
because many breed associations compute their EPDs in separate analyses and each breed
has a different base point. The across-breed adjustment factors allow producers to compare
the EPDs for animals from different breeds for these traits; these factors reflect both the current
breed difference (for animals born in 2021) and differences in the breed base point. The AB-
EPDs are most useful to commercial producers purchasing bulls of more than one breed to use
in cross-breeding programs. For example, in terminal cross-breeding systems, AB-EPDs can
identify bulls in different breeds with high growth potential or favorable carcass characteristics.
The factors are derived by estimating breed differences from the USMARC germplasm
evaluation program and adjusting these differences for the EPDs of the sires that were sampled
in the system. Traits for which factors are estimated are birth weight, weaning weight, yearling
weight, maternal weaning weight (milk), marbling score, ribeye area, backfat depth (fat), and
carcass weight (Table 1). The factors adjust the EPDs to an Angus base (chosen arbitrarily).
As an example, suppose a Red Angus bull has a carcass weight EPD of + 20.0 lb and a
Hereford bull has a carcass weight EPD of + 72.0 lb. The across-breed adjustment factors for
yearling weight (see Table 1) are -6.6 lb for Red Angus and -61.6 lb for Hereford. The AB-EPD
is 20.0 lb – 6.6 lb = 13.4 lb for the Red Angus bull and 72.0 lb – 61.6 = 10.4 lb for the Hereford
bull. The expected carcass weight difference of offspring when both are mated to cows of
another breed (e.g., Braunvieh) would be 13.4 lb – 10.4 lb = 3 lb.
Brahman EPDs for marbling score are reported on a different scale than the other breeds with
marbling score EPDs. For Brahman 400 = Sl00 and 500 = Sm00 whereas for the other breeds,
4.00 = Sl00 and 5.00 = Sm00 meaning the Brahman EPDs are reported on a scale that is 100 times
larger in magnitude. As a result, EPDs from other breeds need to be multiplied by 100 after
being adjusted to Brahman, and Brahman EPDs need to be divided by 100 prior to applying the
adjustment factors. For instance, to adjust a Simmental bull with a marbling score EPD of 0.15
to compare to Brahman bulls using the factors from Table 1, add the Simmental factor, subtract
the Brahman factor, and then multiply by 100: ( 0.15 + ( -0.12 ) – ( -0.70 ) ) * 100 = 73.
Similarly, to adjust a Brahman bull with a marbling score EPD of 40 in order to compare to
Simmental bulls using the same factors, first divide by 100, then add the Brahman factor, and
subtract the Simmental factor: 40 / 100 + ( -0.70 ) – ( -0.12 ) = -0.18.
Please note that as of 2024, yearling weight EPD adjustment factors are derived using a BIF
adjusted postweaning gain and weaning weight as separate traits which is consistent with most
national cattle evaluations. Thus, these factors directly relate to EPDs from national cattle
evaluations.
It is important to note that the table factors (Table 1) do not represent a direct comparison
among the different breeds because of base differences between the breeds. They should only
be used to compare the EPDs (AB-EPDs) of animals in different breeds. To reduce confusion,
breed of sire means (i.e., one half of full breed effect; breed of sire means predict differences
when bulls from two different breeds are mated to cows of a third, unrelated breed) for animals
born in 2023 under conditions similar to USMARC are presented in Table 2.
The adjustment factors in Table 1 were updated using EPDs from the most recent national
cattle evaluations conducted by each of the eighteen breed associations (current as of January
2025). The breed differences used to calculate the factors are based on comparisons of
progeny of sires from each of these breeds in the Germplasm Evaluation Program at USMARC
in Clay Center, Nebraska. These analyses were conducted by USMARC geneticists Larry
Kuehn (email: Larry.Kuehn@ars.usda.gov; ph: 402-762-4352) and Mark Thallman (email:
Mark.Thallman@ars.usda.gov; ph: 402-762-4261).
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