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Understanding EPDs - Hereford
Everyone has an opinion on
the importance of EPDs to their program. While not an exact science the
use of EPD data is an important tool that can be used in all areas of
your herd management and genetic selection. Hereford BW EPD's are on a
fixed scale from 1970 and Red Angus are on a floating scale. We have
attempted to reflect the general explanation and source of each EPD
category. First printed in the Star Lake 2005 Al Semen Guide, this
glossary has generated a huge amount of favorable comments.
CED (Calving Ease-Direct): A positive number or higher number for
this EPD indicates easier calving ease. The CED EPD predicts the ease
with which the progeny of the individual should be born. This EPD is
derived from the calving ease scores turned in, with birth weight for
the animals in the pedigree being a major part of this formula. Consider
selecting for either CE or BW, not both, because doing both
over-emphasizes BW.
BW (Birth Weight): Derived from the actual birth weight ranking
within the contemporary group where the calf was born. The first BW EPD
issued for a calf is the average of the dam and the sire, with an
adjustment made from that number to reflect the actual birth weight of
an individual as compared to its contemporary group average. An actual
birth weight that is exceptionally higher or lower than the average of
its contemporary group will change that individual’s BW EPD accordingly.
The BW EPD is primarily changed when progeny have been recorded from the
subject animal and the accuracy becomes much higher. The birth weight is
adjusted according to the age of dam. The BW EPD has no correlation to
an actual birth weight (an 85 lb. calf can have a BW EPD of 4.5 or 5.5
or 6.5 or even a 2.5 in different herds). A lower number is desirable
and indicates less expected birth weight.
WW (Weaning Weight): An EPD to measure the growth genetics up to
weaning age (205 days). This growth EPD is derived from the weaning
weights turned in for contemporary groups. This EPD is generally very
indicative of the growth up to weaning age, based on the genetic history
of the animals in the pedigree. Actual weaning weights are adjusted for
the age of dam. Weaning weights have been taken and recorded more than
most any other EPD trait. The accuracy is important to the possible
changes of this and all EPDs. The WW EPD has a significant effect on YW
EPD, as well.
YW (Yearling Weight): An EPD to measure the growth from weaning
age to yearling age. The YW EPD is tied to the WW EPD; the growth of the
individual through yearling is effected by weaning weight. This EPD will
be fairly indicative of the genetics in the pedigree as we in the
industry have taken weaning and yearling weights as actual measurements
longer than many traits measured and with fewer adjustments. The
accuracy is important to the YW EPD as to the amount of possible
fluctuation that may occur.
MM (Maternal Milk): An EPD derived from weaning weight to measure
the milking ability of the individual. MM is that part of WW due to a
dam’s milking ability. A proven bull’s milk EPD is derived nearly 100%
from his daughters in production. When a bull is born, his MM EPD is the
average of his sire and dam. The EPD has low accuracy and will change
according to how his sire or dam may change. When his daughters go into
production, the way they produce in their contemporary groups, either by
being above average or below average, will change the sire’s MM EPD
accordingly. At this point the accuracy will go up, which gives a truer
picture of the bull’s actual ability to genetically pass milk to his
progeny. A proven cow’s milk EPD is derived from her own production and
her daughters in production. A cow’s own production contributes to less
than 50% of her own MM EPD. Her daughters in production contribute over
50% to her own MM EPD. The MM EPD has much more meaning for bulls and
cows old enough to have daughters in production.
M&G (Maternal Milk & Growth): This EPD is 1/2 of WW plus MM =
M&G. This EPD is sometimes referred to as Total Maternal or Combined
Maternal. This is an EPD that reflects the combined WW and MM EPD. It
reflects the growth to weaning age plus the milk production to weaning
time. It is an estimate of daughters’ progeny weaning weight.
CEM (Maternal Calving Ease): This EPD indicates the ability of a
sire’s daughters to have a calf at two years of age. Higher or positive
numbers meaning easier calving for the daughter of the individual. Some
of the factors that determine CEM are birth weight, calving ease and
growth of the daughters.
SC (Scrotal Circumference): The SC EPD is the best predictor of
fertility and is also associated with the age of puberty. The higher
number at a younger age may indicate earlier puberty. SC is measured in
centimeters. The SC EPD is adjusted to 365 days. In this genetic
analysis theory, a multiple trait model was used for SC. WW and YW EPD
were used as the predictor variable to increase the accuracy of SC EPD.
FAT (Rib Fat):
Animals with low or negative FAT EPDs are expected to produce leaner
progeny then those with higher FAT EPDs. This EPD measures fat thickness
at the twelfth rib through ultrasound measurements at a year of age on
live animals. These measurements have been shown to be highly correlated
to actual back fat at harvest. All data is done through ultrasound
scale. The more animals that data is collected from on a sire, the more
accurate the EPD will be.
REA (Ribeye Area): This EPD is derived from ultrasound
measurements of live cattle at a year and adjusted to 365 days of age.
The REA EPD is measured in square inches, reflecting the area of the
ribeye. Cattle with a higher REA EPD are expected to produce progeny
that have higher red meat yield at harvest time. The carcass weight also
reflects the yield at harvest time. The more animals that data is
collected from on a sire, the more accurate the EPD.
IMF (Intramuscular Fat): This EPD is derived from the ultrasound
measurement of the intramuscular fat in the ribeye, sometimes called
marbling. Marbling is a term generally used on fat steers at harvest
time. The data is collected on yearling bulls and adjusted to 365 days,
a time period that on a bull correlates to fat steers at harvest. This
EPD is read with the higher number indicating the progeny will have a
higher quality grade at harvest.
BMI$ (Baldy Maternal Index): This index is for the commercial cow
calf producer to maximize profit when Hereford bulls are used on British
cross cows in a rotational crossbreeding program. This index assumes
that the producer raises his own replacements and is retaining ownership
of the balance of the calf crop through harvest, selling on a CHB grid.
This index is an efficiency index that has a negative effect on too much
milk. High milk will result in lower reproductive efficiency and require
more nutrition for the cows. The CEM and CED are also used in this
index, as live calves and less calving difficulty lead to increased
fertility. This index also puts positive weight on WW and negative
Weight on YW. This adds to the efficiency value of Hereford-sired cattle
for the commercial cow calf producer
BII$ (Brahman Influence Index): This index is similar to the
BMI$, with the primary difference being Hereford bulls are used in a
rotational crossbreeding program on Brahman influenced cows rather than
British cows. This index places more importance on fertility and the age
of puberty, and less importance on growth and calving ease. This index
has been designed to place more importance on traits where Brahman
cattle may be more deficient.
CEZ$ (Calving EZ Index): This index is similar to the BMI$. This
index is to measure efficiency and dollar value in the progeny of a
Hereford bull when used by a commercial cow calf producer to breed
yearling heifers. Compared to other indexes, the emphasis has been put
on Calving Ease Direct and Calving Ease Maternal.
CHB$ (Certified Hereford Beef Index): This is a terminal sire
index. This index represents Hereford bulls used on British cross cows
with all progeny sold as retained ownership on a CHB grid. This index
put emphasis on growth and all areas of carcass values.
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