Across Breed EPD Adjustments for 2005 Released

Livestock Update, August 2005

Dr. Scott P. Greiner Extension Animal Scientist, Beef, VA Tech

The table of adjustment factors to estimate across-breed expected progeny differences for various beef cattle breeds was released at the 2005 Beef Improvement Federation Annual Meeting in Sioux Falls, South Dakota. 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 breed research conducted at the U.S. Meat Animal Research Center in Clay Center, Nebraska.

To calculate across breed EPDs, add the adjustment factor found in the table to the within-breed EPD published in the most recent genetic evaluation (2005) for the animals of interest. Across breed EPDs are expressed on an Angus basis (therefore there is not adjustment for Angus EPDs). 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 YW EPD of +70 and the Charolais bull has a YW EPD of +40. To fairly compare the YW 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 YW EPD of +91.8 (70 + 21.8 = 91.8) and the Charolais bull an across-breed YW EPD of +93.2 (40 + 53.2 = 93.2). Comparison of the calculated across-breed EPDs for these two bulls suggests they would transmit similar genetics for yearling growth as the difference in their across-breed YW EPDs is minimal. Both of these bulls are similar to an Angus bull with a YW EPD of +90.

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 as well as optimizing heterosis. By using the across breed EPD adjustment factors it can be determined that an Gelbvieh bull with a Milk EPD of +18 and a Simmental bull with a Milk EPD of +10 are similar to an Angus bull with a Milk EPD of +20. In other words, sires with these within breed EPDs would be estimated to transmit similar genetic potential for milk production to their daughters.

Without across-breed adjustment factors, EPDs for animals of different breeds cannot be accurately 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. These adjustment factors should be utilized only with current EPDs published by the breed associations.

2005 Adjustment Factors to Add to EPDs of Various Breeds to Estimate Across-Breed EPDs
Breed	Birth wt.	Weaning wt.	Yearling wt.	Milk
Angus	0.0	0.0	0.0	0.0
Braunvieh	6.0	30.2	12.8	22.4
Charolais	10.0	38.8	53.2	1.8
Gelbvieh	4.7	6.3	-22.3	2.4
Hereford	2.9	-1.8	-14.2	-18.8
Limousin	4.0	1.8	-20.8	-16.2
Red Angus	3.1	-1.0	0.7	-6.8
Salers	4.2	29.0	42.3	9.9
Simmental	5.9	22.8	21.8	10.1
Tarentaise	3.1	30.6	13.1	18.3

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