Quick Reference to ASA EPDs and $ Indexes
Expected Progeny Differences (EPDs):
EPDs are the most accurate and effective tool available
for comparing genetic levels. In using EPDs, the difference between two sires’ EPDs represents the unit
difference expected in the performance of their p rogeny. For example, if sires A and B have EPDs of +10
and
–
5, a 15-unit difference would be expected in their progeny (moving from -5 to +10 y ields 15 units).
Key to using EPDs is knowing what units they are expressed in. For example, if the above case referred to
weaning weight EPDs, A would be expected to sire 15-
pounds
more
weaning weight
than B. If calving
ease were the trait, A would be expected to sire 15-
percent
mo re
unassisted births
in first-calf heifers; in
o
ther words, if B sired 30 assists in a group of 100 heifers, we’d expect A to require 15 assists. A
percentile-
ranking chart is required to determine where a bull’s EPDs rank h im relat ive to other bulls in the
breed. For percentile rankings or more detailed information about EPDs and $ indexes visit
. Listed below are the units ASA EPDs are expressed in:
All-Purpose Index (API):
Dollars per cow
exposed under an all-purpose-sire scenario. (See
below for more details.)
Average Daily Gai n (ADG):
Pounds of post-
weaning daily weight gain.
Back Fat (BF)
: Inches
of backfat.
Birth Weight (BW):
Pounds of birth weight.
Cal vi ng Ease (CE):
Percent of unassisted births
when used on heifers.
Carcass Weight (CW):
Pounds of carcass
weight.
Docility (DOC):
Percent of offspring achiev ing
a docile (1) score.
Maternal Cal ving Ease (MCE):
Percent of
unassisted births in first-calving daughters.
Milk (MLK):
Pounds of weaning weight due to
milk.
Marbling (MRB):
Marb ling score.
Maternal Weaning Weight (MWW):
Pounds
of weaning weight due to milk and growth.
Ri beye Area (REA):
Square inches of ribeye.
Warner-Bratzler Shear Force (WBSF):
Pounds of force required to shear a steak.
Stayability (STAY):
Percent of daughters
remain ing in the cowherd at 6 years of age.
Terminal Index (TI):
Dollars per cow exposed
under a terminal-sire scenario. (See below for
more details.)
Weaning Weight (WW):
Pounds of weaning
weight.
Yearling Weight (YW):
Pounds of yearling
weight.
Yiel d Grade (YG):
Yield grade score.
$ Indexes:
Though EPDs allow for the comparison of genetic levels for many economically important
traits, they only provide a piece of the economic puzzle. That’s where $ indexes come in. Through well
-
conceived, rigorous mathematical computation, $ indexes blend EPDs and economics to estimate an
animal’s overall impact on your bottom line. The same technology that led to the dramatic progress in
swine, poultry and dairy genetics over the last several decades was used to develop the following $ indexes:
All-Purpose Index (API):
Evaluates sires for use on the entire cow herd (b red to both Angus first-calf
heifers and mature cows) with the portion of their daughters required to maintain herd size retained and the
remain ing heifers and steers put on feed and sold grade and yield.
Terminal Index (TI):
Evaluates sire for use on mature Angus cows with all offspring put on feed and sold
grade and yield.
Using API and TI
:
First, determine wh ich index to use; if you’re keep ing replacements use API, if not, TI.
Then, just as with EPDs, zero in on the unit difference between bulls. (As described above, indexunits are
in dollars per cow exposed.) The difference can be used to determine how much a bull is worth compared
to another. Or, put another way, how much you can pay for one bull compared to another. For examp le,
when buying an all-purpose-type sire, you can quickly figure a bull scoring +100 for API is worth an ext ra
$6,000 over a +50 bull if both are exposed to 30 cows over 4 years ($50 d iff. x 30 hd. x 4 yr. = $6,000). A
percentile-
ranking chart is required to determine where a bull’s indexvalue ranks him relative to other bulls
in the population. For percentile rankings or more detailed informat ion about EPDs and $ indexes visit
.
Important disclaimer
: DO NOT compare index values of purebreds of different breeds, hybrids of
different breed composition or purebreds with hybrids
—
our systemwas not developed to make valid
comparison among these groups. Therefore, you must first determine the breed and breed composition
appropriate for your herd and use indexvalues to compare animals within that population.
