Fitting EPDs Into Your Selection System
Estimated Progeny Differences (EPDs) are powerful genetic evaluation calculations. But how do you actually use these values or fit them into your selection program on the farm?
One thing to remember is that the EPDs are only an additional tool
for your toolbox. In reality, EPDs take some of the information
that you normally like to keep in your head and translate that into
a number for each animal. For example, your favorite ewe is the
favorite for a number of reasons. Perhaps, she always has twins
that are a good size and her mother also had a lot of twins and
the daughters you have kept from her also have good sized twins.
It is easy to recall this information for your favorite ewe(s) and
maybe even for your worst ewes. But, if you have 100 ewes it may
be difficult to be sure how that information relates for each and
every one of those 100 ewes. EPDs take all of the information on
how the ewe performed and how the ewe's relatives have performed
and give the ewe a ranking compared to other ewes of the same breed.
The amount of information used in the EPD is limited compared to
what many producers keep in their memory for favorite animals. Generally,
EPDs are fairly specific for example, number of lambs born per lambing.
This doesn't take into account the fact that the ewe was in the
wrong group and didn't get flushed like the rest of the group for
one lambing. It also doesn't consider that the ewe is on an accelerated
lambing program and she's been averaging 3 lambs born per year but
only 2 lambs born per lambing.
EPDs are based on statistics. The statistics tend to use a lot of averaging of numbers. As a result, if you use the EPD values, on average you will make more improvement in the trait than if you do not. However, the average is made up of individual animals. Individuals do not always fit averages very well. So, don't get discouraged if the values on one animal don't fit with the performance that you see on the farm. If the accuracy on the animal is low, the EPD value can change dramatically as more information is added.
|Author:||Delma Kennedy - Sheep Specialist, Genetics, Reproduction and Performance/OMAFRA|
|Creation Date:||03 December 2003|
|Last Reviewed:||13 April 2010|