What are EPD's? (Estimated Progeny
Differences)
By Mike Safley
An EPD is an estimate of the genetic merit of an animal for a
single trait. The EPD is the expected difference between the performance
of an animal's progeny for a specific trait and the average progeny
performance, for that trait, of all the animals in the breed at
the time the genetic evaluation program is established. Changes
in mean EPDs over time quantify the long-term genetic improvement
that has been achieved.
How are EPDs calculated?
Alpaca breeders need to record the performance values for their
animals. This information would be posted to a central database
via a web-based tool. Most of the necessary information would be
compiled from a fleece report or histogram, (Information graph)
and then downloaded into a central database. The data would come
from alpacas reared under many different management systems.
A computer software program then identifies the genetic linkages
between the alpacas across years. The dataset for the alpacas will
include all the data from previous years, for all the relatives,
across generations. The EPD calculations include data from related
traits, because an animal's performance in any trait gives information
on how it will perform in a similar trait (for example, fleece weight
and staple length). These calculations produce EPD values on every
trait for every alpaca herdsire, dam and cria in the system. And
these EPDs are recalculated, annually, after the performance records
from each new production cycle are entered into the database.
EPDs are not constants; they are estimates of genetic merit that
change over time as new information accumulates on an animal and
its relatives. Thus each year results in a new set of EPDs for all
animals, with progressive increases in the accuracy of the estimates
and in the breeders’ ability to discriminate among prospective breeding
animals.
How are EPDs reported?
An EPD is reported in the normal units for the trait, such as +0.75
pounds (for fleece weights) or -0.4 microns (for fiber diameter).
It's important to note that an EPD value is not a ratio or an index.
EPDs are expressed as deviations (+ or -) from the average population
value, which is considered to be zero. This average of the herd’s
performance, which is used to establish the baseline (zero) for
comparison purposes, might be recalculated periodically, probably
every five years. EPDs always have a positive (+) or negative (-)
sign in front of them. (See
Table 12.2)
The positive and negative symbols don't always mean better or worse--it
depends on the particular trait. For example, a fleece weight of
+0.75 pounds is good but a Fiber Diameter EPD of -0.3 microns can
also be good, i.e. finer fiber. These EPDs are used to compare herdsires,
for instance, a stud with a fleece weight EPD of +3.0 is good, but
a different stud with a fleece weight EPD of +4.0 is better. EPDs
may take a little getting used to, but once you get the hang of
them, they give the most objective and reliable estimation of genetic
value possible.
All of the individual records that are collected by the entity
processing the data, usually a university, are kept confidential.
The EPDs for individual animals are reported to the owners. The
collective results are made available to the participating breeders
in the form of genetic evaluation reports
CAN HERDSIRES BE COMPARED UNDER DIFFERENT MANAGEMENT
CONDITIONS?
The calculation of EPDs uses data from many different flocks, and
this procedure is mathematically valid across herds, so long as
none of the herds is genetically isolated from the others. But the
feed regimen at all farms must be good enough to permit good performance.
Reproduced with permission from:
Alpaca
Breeding Farm: Northwest Alpacas: raising suri and
huacaya alpacas for sale, alpaca investment, and alpaca business
plans for alpaca breeders and owners worldwide. Find more useful
information at the Alpaca
Library.
Copyright © 2003-2005 Northwest Alpacas
Maple
Tree Alpaca Farm | Alpaca
Library Information
|
