The concept of EPDs was first introduced to Senepol producers over 10 years
ago with the first publication of a National Sire Evaluation. An Expected Progeny
Difference (EPD) is an estimate of the genetic merit of an animal as a parent
and is reported in the normal units of measurement such as pounds or
centimeters. Nearly every major beef breed association in the United States
publishes an annual or semi-annual summary of sire EPDs. The SCBA
conducts annual genetic evaluations and publishes an annual sire summary for
birth weight, weaning weight, yearling weight, maternal milk, maternal weaning
weight and scrotal circumference.

An EPD means absolutely nothing by itself, and it does not predict specific
levels of performance. An EPD should only be used to make comparisons
between individuals. For example, let's say a sire has a weaning weight EPD of
+15 lb. This does not indicate that you would increase weaning weight in your
herd by 15 lb. if you were to use this sire, nor does it mean his progeny will
weigh any certain amount at weaning. One individual EPD means nothing until
you have another EPD to compare it with.

Consider another example. Sire A has a birth weight EPD of -3 lb. and Sire B's
birth weight EPD is +1 lb. When used in your herd, you would expect Sire B's
calves to weight 4 lb. (1 lb. minus -3 lb.) more than A's calves, if mated to a
comparable group of cows. This 4-lb difference is also only an average value. If
you had one calf by each sire, these two calves would probably not be exactly 4
lb. different at birth. As you increase the number of calves in your herd by each
of these two sires though, the average birth weight difference between the two
sire groups should come closer to 4 lb. In addition to birth weight, similar
examples could be given for weaning weight, yearling weight and scrotal
circumference. These four EPDs are termed "direct" EPDs and pertain to a
parent's own progeny.

Another category of EPDs, termed "maternal", includes Maternal Milk EPD.
Maternal Milk EPDs pertain to a sire's daughters calves or in other words a
sire's maternal grand progeny. A Maternal Milk EPD predicts the difference in
average weaning weight of sires' daughters' progeny due strictly to milking
ability. Maternal Milk EPDs are expressed in pounds of calf weaned due to milk
production, not actual pound of milk produced by the dam. For example sire A
has a Maternal Milk EPD of 2 lb. and sire B has a Maternal Milk EPD of 14 lb.
Daughters of sire B should produce progeny with 12-lb (14 lb. minus 2 lb.)
heavier weaning weights than daughters of sire A. This 12-lb difference would
be due to total milk production over the entire lactation period of approximately
205 days.

A calf's weaning weight is genetically influenced by his own genes for growth
(half of these genes come from each parent) along with his dam's milk
production. Weaning Weight EPDs are an indication of the calf's genes for
growth, while Maternal Milk EPDs are an indication of the dam's milk production.
Because of the direct and maternal genetics that influence a calf's weaning
weight, a final type of EPD is published in the Senepol Sire Summary. This is
termed Maternal Weaning Weight EPD.

Maternal Weaning Weight EPD reflects both a sire's influence for direct genetics
for a calf's growth and the maternal genetics for his daughters milk production.
Maternal Weaning Weight EPD is simply a mathematical combination of
Weaning Weight EPD and Maternal Milk EPD. Maternal Weaning Weight EPD =
(1/2 X Weaning Weight EPD) + (Maternal Milk EPD). A sire transmits one-half
his genes for weaning weight to his daughters, the daughters in turn transmit
one-half of there genes for weaning weight to their offspring, thus a sire's grand
progeny actually receive 1/2 of a sire's Weaning Weight EPD. A sire's entire
Maternal Milk EPD is an indication of his daughter's milk production.
As an example, say sire A has a Maternal Weaning Weight EPD of 30 lb. and
sire B's Maternal Weaning Weight EPD is 5 lb. You would expect weaning
weights of daughters calves to be 25 lb. (30 lb. minus 5 lb.) heavier for sire A.
Again this is a result of direct genetics for a calf's weaning growth and the
genetics for the dam's milk production. Maternal Weaning Weight EPD is
sometimes referred to as "combined maternal", "growth plus milk" or "total
maternal" EPD.

Expected Progeny Differences should never be compared across breeds. All
national evaluations are always conducted within breed, therefore the values
from these evaluations are relative to cattle within that breed only. A Senepol, a
Hereford and a Simmental sire may all have equal yearling weight EPDs of 20
lb., but you can not expect all three sires to be genetically equal for yearling
weight. You simply can not and should not make any genetic comparisons
between breeds based on EPDs.

This does not mean you must have one pure-breed of cattle to utilize EPDs.
When making sire selections, commercial cattle producers actually have as
much to gain from utilizing EPD information as purebred producers. Sires must
be within the same breed to compare EPDs, but these values are applicable
when sires are mated to cows of a different breed or even crossbred cows.
One great advantage of Senepol Sire Summary is that EPDs of all proven active
sires are published. There is not a perfect bull for all to utilize. One bull may
work best in one situation, while completely different bull will work better in
another situation. Consequently in the Senepol Sire Summary, there is an entire
range between high and low EPDs for each trait. Therefore, there are probably
many sires available that are suitable for nearly every production system.