Download Understanding and Using Expected Progeny Differences

Using Carcass EPD for Profit
by Robert E. Williams, Ph. D.
AICA Director of Breed Improvement and Foreign Marketing
Identifying genetic differences between
animals in the Charolais breed for
economically important traits so that
producers can make informed selection
decisions that will enhance the
production of superior animals in the
next generation. This is how I would
define the purpose of the Charolais
genetic evaluation programs. With the
recent release of carcass Expected
Progeny Differences (EPD) more
questions arise about using EPD for trait
selection.
An EPD is a prediction of how future
progeny of a sire are expected to
perform in a particular trait relative to other animals in the analysis. The key word is
"difference". The EPD itself does not imply "good" or "bad" performance. But rather, the
EPD gives a prediction of the average difference to expect in the performance of a sire's
progeny to other sires in the same analysis.
Expected Progeny Differences are accompanied with an Accuracy (ACC) value. Accuracy is
a measure of reliability regarding the EPD evaluation for a performance trait. Accuracy is
reported as a decimal number between zero and one. Large ACC values indicate greater
accuracy and more certainty that the EPD will show little change as additional progeny
information is obtained. Consult the AICA Sire Summary for more information about
accuracy values.
Within any group of animals we observe a range in performance values, for example, a group
of fat steers may range from .20 inches to .60 inches fat thickness at the 12th rib. Only a
portion of this phenotypic variation that we observe in a group is due to genetics, the
remaining portion of variation is due to the environment. The portion of the phenotypic
differences due to the genetics of the animal is called heritability (h2). Because the heritability
of economically important traits in beef production is not 1, a large portion of the variation we
observe is due to environmental effects. Therefore, using the same cow herd and herd bulls
each year often gives us different performance results in our herd. For example, during a
year of a drought weaning weights may be down (500 pound average weaning weight for
example). But the next year weaning weights may be up (650-pound average weaning
weight) due to more rainfall and better grass. For this reason EPD do not predict actual
performance but rather differences to expect between sires.
Expected progeny differences are typically expressed in the same unit of measurement as
performance records (pounds, inches, etc) as a plus or minus value such as 0.20 or -0.03
square inches for ribeye area for example. Birth weight, weaning weight, yearling weight,
milk, and hot carcass weight are all traits that are expressed in pounds. Ribeye area is
expressed in square inches, fat thickness in inches and marbling in terms of the USDA
marbling score (see USDA Quality Grading System and Marbling Score Table). By taking
the difference between the EPD of two sires the comparison of progeny differences that can
be expected when mated to an infinite number of genetically identical cows in the same
environment can then be made.
Results of a research project are given below to help understand how EPD can be used in
breeding programs. This study was completed at the University of Nebraska by Vieselmeyer
et al.. The objective was to evaluate the impact of EPD for marbling on progeny production
and carcass traits. Six Angus bulls with high marbling (HIGH) and six with low marbling EPD
(LOW) were selected from the American Angus Association Sire Summary and mated to
MARC II cows and heifers at the Dalbey-Halleck Farm (Virginia, NE). Approximately 250
progeny of the six bulls were produced for this project with the progeny being slaughtered at
two different endpoints (.25 and .50 inches fat thickness) indicated below as either GROUP 1
or GROUP 2. Slaughter group 2 was fed approximately 2 months longer than slaughter
group 1. The EPD and progeny results listed below are averages of the sire groups and
progeny.
Progeny Carcass Results
Group 1 at Slaughter
HIGH
LOW
0.33
602
52 %
2.4
11.29
0.35
617
17%
2.4
11.50
Group 2 at Slaughter
Fat Thickness (inches)
Carcass Weight (pounds)
% Choice
USDA Yield Grade
Ribeye Area (sq. inches)
HIGH
LOW
0.51
736
96%
3.0
12.70
0.51
752
78 %
2.9
13.10
While days on feed had a significant impact on the percentage of cattle grading choice, the
difference between the High and Low marbling sires was clearly reflected within each
slaughter group. The same trend was evident in the other traits as well. Selection based on
EPD resulted in similar differences in the carcass results of progeny. Another project at the
University of Georgia using several of the same bulls had similar results. In this study the
bulls were mated to straight Angus cows and fed to older ages. While the percentage of
choice increased, the differences in EPD for carcass traits were reflected in differences in
carcass performance traits. Both projects have indicated that selection based on values
expressed as EPD resulted in predictable differences in slaughter progeny. It was also
shown that selection for increased marbling is possible without increasing fat thickness at the
12th rib.
These and other projects have indicated how growth and carcass EPD could be used to
match genetics to a particular marketing grid and management scenarios depending on the
premiums and discounts in the market place. Selection for additional growth and ribeye area
and less fat would be beneficial in scenarios were little premium was available for increased
marbling.
It also exhibits how a producer could apply management skills such as extending the feeding
period with growthier cattle to achieve a higher percentage of choice cattle while maintaining
a desirable yield grade by combining management ability and genetic selection. A complete
understanding of the genetics of the cattle and how to manage cattle with different genetic
backgrounds is essential to maximizing the efficiency of the various groups of cattle that a
feeder or producer may encounter.
When EPD are available for multiple traits the producer is given the opportunity to select for
numerous traits that will have an economic impact on herd profitability, even when those
traits may be antagonistic to each other. For example, producers now have the ability to
select for increased marbling without changing fat thickness or they may select for lower birth
weights and increased growth. With carcass EPD available for Charolais cattle, producers
now have the ability to apply selection pressure to more traits that dictate profitability in
commercial cowherds. Producers must combine genetic selection for multiple traits to
different management and marketing scenarios to increase profitability.