Across Breed EPD Adjustments for 2003

Livestock Update, August 2003

Scott P. Greiner, Ph.D., Extension Animal Scientist, Beef, Virginia Tech

The table of adjustment factors to estimate across-breed expected progeny differences for various beef cattle breeds was released at the 2003 Beef Improvement Federation Annual Meeting in Lexington, Kentucky. 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, Nebraska and adjusted to a year 2001 base using EPDs from the most recent national cattle evaluations.

To calculate across breed EPDs, simply 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 or a Charolais bull to use as a terminal sire on mature Angus-based cows. The Simmental bull has a YW EPD of +60 and the Charolais bull has a YW EPD of +25. To fairly compare the YW EPDs of these two bulls of different breeds, the EPDs must first be adjusted to a common equivalent using the across-breed table. Using the table, the Simmental bull would have an across-breed YW EPD of +81.1 (60 + 21.1 = 81.1) and the Charolais bull an across-breed YW EPD of +82.8 (25 + 57.8 = 82.8). In this example, we would expect the growth rate of the progeny of the Simmental bull and Charolais bull to be very similar on average, since their across-breed YW EPDs are very similar (across breeds EPDs of 81.1 vs. 82.8).

The adjustment factors 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. For example, using the adjustments, it can be demonstrated that a Gelbvieh bull with a milk EPD of +16 will add similar milk genetics when compared with an Angus bull with a milk EPD of +20 (both the bulls would be +20 on an across-breed basis). This example demonstrates the differences between the breeds that exist- a Gelbvieh bull with a +16 milk EPD ranks in the lower 30% of the Gelbvieh breed for milk genetics, whereas the Angus bull with a milk EPD of +20 ranks in the top 30% of the breed. With this in mind, a Gelbvieh bull can be selected to compliment an Angus cow base that will add a moderate amount of milk. Similar calculations can be made for other breeds, as well as for other traits such as birth and weaning weight. The key is to recognize the basic genetic differences between breeds, and then select bulls within those breeds with optimum genetics while avoiding extremes.

The accuracy of across-breed EPDs depends primarily on the accuracy of the within-breed EPDs for the individual animals being compared. Additionally, the across-breed EPD adjustment factors presented here should only be applied to EPDs generated from the most recent national cattle evaluations (Spring 2003 Sire Summaries).

2003 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	6.6	30.3	13.5	23.1
Charolais	10.5	41.1	57.8	2.0
Gelbvieh	5.3	7.9	-20.3	3.8
Hereford	3.3	-2.4	-15.1	-16.2
Limousin	5.8	23.5	20.5	0.2
Red Angus	3.6	-1.2	-0.1	-10.7
Salers	5.1	28.4	40.6	11.3
Shorthorn	7.8	31.2	44.5	12.0
Simmental	6.4	21.6	21.1	9.0
Tarentaise	3.6	29.8	12.8	17.8

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