Expected progeny differences (EPDs) have resulted in substantial, positive genetic change in the cattle industry since their inception in the 1970s. However, because breed associations often use different national evaluation programs, EPDs of animals from different breeds cannot be compared because most breed associations compute their EPDs in separate analyses and each breed has a different base point.
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. These are called across-breed EPD (ABEPD) adjustment factors.
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 2016) and differences in the breed base point.
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. The traits for which factors are estimated are birth weight, weaning weight, yearling weight, maternal weaning weight (milk), marbling score, ribeye area, backfat depth, and carcass weight (Table 1). These factors adjust the EPDs to an Angus base (chosen arbitrarily).
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 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 18 breeds.
The ABEPDs 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, ABEPDs can identify bulls in different breeds with high growth potential or favorable carcass characteristics.
As an example, suppose a Charolais bull has a weaning weight EPD of + 25.0 lbs. and a Hereford bull has a weaning weight EPD of + 70.0 lbs. The across-breed adjustment factors for weaning weight (see Table 1) are 32.7 lbs. for Charolais and -16.5 lbs. for Hereford. The ABEPD is 25.0 lbs. + 32.7 lbs. = 57.7 lbs. for the Charolais bull and 70.0 – 16.5 = 53.5 lbs. for the Hereford bull.
The expected weaning weight difference of offspring when both are mated to cows of another breed (e.g., Angus) would be 57.7 lbs. – 53.5 lbs. = 4.2 lbs.
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 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 2016 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 18 breed associations (current as of December 2018).
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 US MARC in Clay Center, NE. These analyses were conducted by US MARC geneticists Larry Kuehn and Mark Thallman.
Future release of ABEPD factors
The ABEPD factors were traditionally derived and released during the annual Beef Improvement Federation (BIF) conference each year. However, this is not ideal for commercial producers buying bulls in the spring or fall season.
A BIF working group recommended a plan to begin releasing the ABEPD factors near the beginning of each year to facilitate the use of these tools during spring bull buying. That began last year.
Additional updates may be released throughout the year, particularly if breeds are aware of significant changes to their evaluations, such as base adjustments. As of now, changes to the factors will be reported on the BIF website (www.beefimprovement.org); for instance, we are working to update information for the marbling adjustment factor in Brahman. — BIF