BLACKSBURG, Va. – The table of adjustment factors to estimate across-breed expected progeny differences for various beef cattle breeds was released at the 2004 Beef Improvement Federation Annual Meeting in Sioux Falls, S.D.
By using the across-breed adjustment factors, animals of different breeds can be compared on the same EPD scale.
The adjustment factors are based on comparative studies of the breeds conducted at the U.S. Meat Animal Research Center in Clay Center, Neb.
Calculations. To calculate across breed EPDs, add the adjustment factor found in the table to the within-breed EPD calculated in the most recent genetic evaluation for the animals of interest.
As an example, assume we are considering a Simmental bull vs. a Charolais bull to use as a terminal sire on mature Angus-based cows.
The Simmental bull has a yearling weight EPD of +70 and the Charolais bull has a yearling weight EPD of +40.
To fairly compare the yearling weight 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 yearling weight EPD of +91.9 (70 + 21.9 = 91.9) and the Charolais bull an across-breed yearling weight EPD of +93.4 (40 + 53.4 = 93.4).
Comparison of the calculated across-breed EPDs for these two bulls suggests the growth rate of their offspring would be similar on average as the difference in their across-breed yearling weight EPDs is minimal.
Uniformity. Across-breed EPDs are most useful in managing uniformity when multiple breeds are rotated in a crossbreeding system to avoid large fluctuations in traits such as birth weight and milk.
Uniformity from one generation to the next when using sires of different breeds can be improved by selecting bulls with similar across-breed EPDs.
A common challenge to overcome in crossbreeding systems is to avoid large differences in traits such as calving difficulty, cow size, and milk production resulting from use of breeds that are largely divergent for these traits.
Across-breed EPDs are a tool to manage these potential differences, while favorably utilizing the basic genetic differences between breeds that exist and optimizing heterosis.
Don’t go without it. Without across-breed adjustment factors, EPDs for animals of different breeds cannot be 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 = 0) used in the calculation of EPDs for each breed.
For these reasons, the adjustment factors alone are not reflective of breed differences.
The accuracy of across-breed EPDs is primarily associated with the accuracy of the within-breed EPDs for the individual animals being compared.
(The author is a extension animal scientist with a focus on beef at Virginia Tech.)
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