An animal's breeding value is
its genetic merit, half of which will be passed on to its progeny. While we will never know the exact breeding
value, for performance traits it is possible to make good estimates. These estimates are called Estimated Breeding
Values (EBVs).
In the calculation of EBVs, the
performance of individual animals within a contemporary group is directly
compared to the average of other animals in that group. A contemporary group consists of animals of
the same sex and age class within a herd, run under the same management
conditions and treated equally. Indirect
comparisons are made between animals reared in different contemporary groups,
through the use of pedigree links between the groups.
EBVs are expressed in the units
of measurement for each particular trait.
They are shown as + ive or - ive differences between an individual
animal's genetics difference and the genetic base to which the animal is
compared. For example, a bull with an
EBV of +50 kg for 600-Day Weight is estimated to have genetic merit 50 kg above
the breed base of 0 kg. Since the breed
base is set to an historical benchmark, the average EBVs of animals in each
year drop has changed over time as a result of genetic progress within the
breed.
The absolute value of any EBV
is not critical, but rather the differences in EBVs between animals. Particular animals should be viewed as being
"above or below breed average" for a particular trait.
Whilst EBVs provide the best
basis for the comparison of the genetic merit of animals reared in different
environments and management conditions, they can only be used to compare
animals analysed within the same analysis.
Consequently, Hereford BREEDPLAN EBVs cannot be validly compared with
EBVs for any other breed.
Although EBVs provide an
estimate of an animal’s genetic merit for a range of production traits, they do
not provide information for all of the traits that must be considered during
selection of functional animals.
In all situations, EBVs should be used in conjunction with visual
assessment for other traits of importance (such as structural soundness,
temperament, fertility etc). A
recommended practice is to firstly select breeding stock based on EBVs and to
then select from this group to ensure that the final selections are otherwise
acceptable.
EBVs are published for a range
of traits covering fertility, calving ease, milking ability, growth, carcase
merit and feed efficiency. When using
EBVs to assist in selection decisions it is important to achieve a balance
between the different groups of traits and to place emphasis on those traits
that are important to the particular herd, markets and environment. One of the advantages of having a
comprehensive range of EBVs is that it is possible to avoid extremes in particular
traits and select for animals with balanced overall performance.
Calving Ease
EBVs (%) are based on
calving difficulty scores, birth weights and gestation length information. More positive EBVs are favourable and
indicate easier calving.
CE % Direct = Direct Calving Ease - The EBV for direct
calving ease indicates the influence of the sire on calving ease in purebred
females calving at two years of age.
CE % Daughters = Daughters' Calving Ease - The EBV for
daughters' calving ease indicates how easily that sire's daughters will calve
at two years of age. It consists of the
maternal component and half the direct component (ie CE maternal + ½ CE
direct).
Gestation
Length EBV (days) is an
estimate of the time from conception to the birth of the calf and is based on
AI and hand mating records. Lower
(negative) GL EBVs indicate shorter gestation length and therefore easier
calving and increased growth after birth.
Birth Weight
EBV (kg) is based on the measured birth
weight of progeny, adjusted for dam age.
The lower the value the lighter the calf at birth and the lower the
likelihood of a difficult birth. This is
particularly important when selecting sires for use over heifers.
200-Day Growth
EBV (kg) is calculated
from the weight of progeny taken between 80 and 300 days of age. Values are adjusted to 200 days and for age
of dam. This EBV is the best single
estimate of an animal's genetic merit for growth to early ages.
400-Day Weight
EBV (kg) is calculated
from the weight of progeny taken between 301 and 500 days of age, adjusted to
400 days and for age of dam. This EBV is
the best single estimate of an animal's genetic merit for yearling weight.
600-Day Weight
EBV (kg) is calculated
from the weight of progeny taken between 501 and 900 days of age, adjusted to
600 days and for age of dam. This EBV is
the best single estimate of an animal's genetic merit for growth beyond
yearling age.
Mature Cow
Weight EBV (kg) is based on the cow weight when the
calf is weighed for weaning, adjusted to 5 years of age. This EBV is an estimate of the genetic
difference in cow weight at 5 years of age and is an indicator of growth at
later ages and potential feed maintenance requirements of the females in the
breeding herd. Steer breeders wishing to
grow animals out to a larger weight may also use the Mature Cow Weight EBV.
Milk EBV (kg) is an estimate of an animal's milking ability. For sires, this EBV indicates the effect of
the daughter's milking ability, inherited from the sire, on the 200-day weights
of her calves. For dams, it indicates
her milking ability.
Scrotal Size
EBV (cm) is calculated from the
circumference of the scrotum taken between 300 and 700 days of age and adjusted
to 400 days of age. This EBV is an
estimate of an animal's genetic merit for scrotal size. There is also a small negative correlation
with age of puberty in female progeny and therefore selection for increased
scrotal size will result in reduced age at calving of female progeny.
Days to
Calving EBV (days) indicates the fertility of the
daughters of the sire. It is the time
interval between when the female is first exposed to a bull in a paddock mating
to the day when she subsequently calves.
A negative EBV for days to calving indicates a shorter interval from
bull-in date to calving and therefore higher fertility.
Carcase Weight
EBV (kg) is based on abattoir carcase
records and is an indicator of the genetic differences in carcase weight at the
standard age of 650 days.
Eye Muscle
Area EBV (sq cm) is calculated
from measurements from live animal ultrasound scans and from abattoir carcase
data, adjusted to a standard 300 kg carcase.
This EBV estimates genetic differences in eye muscle area at the 12/13th
rib site of a 300 kg dressed carcase.
More positive EBVs indicate better muscling on animals. Sires with relatively higher EMA EBVs are
expected to produce better-muscled and higher percentage yielding progeny at
the same carcase weight than will sires with lower EMA EBVs.
Rib Fat and Rump
Fat EBVs (mm) are
calculated from measurements of subcutaneous fat depth at the 12/13-rib site
and the P8 rump site (from live animal ultrasound scans and from abattoir
carcases) and are adjusted to a standard 300 kg carcase. These EBVs are indicators of the genetic
differences in fat distribution on a standard 300 kg carcase. Sires with low, or negative, fat EBVs are
expected to produce leaner progeny at any particular carcase weight than will
sires with higher EBVs.
Retail Beef
Yield EBV (%) indicates genetic differences
between animals for retail yield percentage in a standard 300 kg carcase. Sires with larger EBVs are expected to
produce progeny with higher yielding carcases.
Intramuscular
Fat EBV (%) is an estimate of the genetic
difference in the percentage of intramuscular fat at the 12/13th rib site in a
300 kg carcase. Depending on market targets, larger more positive values
are generally more favourable.
Docility EBV (%) is calculated from docility scores
taken at weaning or shortly afterwards.
This EBV is an estimate of the genetic difference in the percentage of
progeny that will be scored as docile or restless (scores 1 or 2).
Net
Feed Intake (Feedlot Finishing) EBV
(kg) is an estimate of genetic differences between animals in feed intake at a
standard weight and rate of weight gain when animals are in a feedlot finishing
phase. NFI-F EBVs as expressed as
kilograms (kg) of feed intake per day.
Lower, or more negative, NFI-F EBVs are more favourable. For example, a bull with an NFI-F EBV of –0.6
kg/day would be expected to produce progeny that eat less feed per day than the
progeny from a bull that has an NFI-F EBV of +0.8 kg/day (when the progeny are
of similar weight, are growing at a similar rate, and are in a feedlot
finishing phase).
Hereford selection indices are
calculated for four production/market specifications, namely, Southern Self
Replacing, Northern Self Replacing, Southern Baldy Maternal and Northern Baldy
Terminal.
Each selection index describes
a different production/market scenario and relates to a typical commercial herd
using Hereford bulls. Producers are
advised to use the selection index that most closely aligns to their production
system. All four selection indexes are focussed on maintaining and improving
eating quality. Significant premiums are
applied for increasing marble score up to a marble score of 3. Pressure is also applied to early life growth
to maintain low ossification scores and good MSA compliance. In addition, each
selection index targets the following specifications.
Index values are reported as
EBVs, in units of relative earning capacity ($’s) for a given market. They reflect both the short-term profit
generated by a sire through the sale of his progeny, and the longer-term profit
generated by his daughters in a self-replacing cow herd. Note that different types of animals can give
similar profit values, so consideration should be given to both the index and
the component EBVs when selecting animals for a particular production
system. More information is available on
selecting animals using a selection index.
The Index values are derived
using BreedObject technology. More
information is available from the BreedObject web site.
Southern
Self-Replacing Index - Estimates the genetic differences between animals
in net profitability per cow joined in a commercial self-replacing straight
bred Hereford herd targeting the domestic market. Daughters are retained for breeding and so
maternal traits are of importance.
Steers are slaughtered at 20 to 22 months of age to produce 300 kg
carcases with 10 mm P8 fat depth. A
moderate cost is applied for cow feed costs during the annual feed shortage
period.
Northern
Self-Replacing Index - Estimates the genetic differences between animals
in net profitability per cow joined in a commercial self-replacing herd
targeting the domestic market. This
index is suitable for use by both straight bred Hereford herds and in
crossbreeding programs where Hereford bulls are being used over a Bos indicus
based cow herd (e.g. flatback).
Daughters are retained for breeding and so maternal traits are of
importance. Steers are slaughtered at 20
to 22 months of age to produce 340 kg carcases with 12 mm P8 fat depth. A high cost is applied for cow feed costs
during the annual feed shortage period.
Southern Baldy
Maternal Index - Estimates the genetic differences between animals
in net profitability per cow joined in a commercial crossbred herd using
Hereford bulls over Bos taurus females (e.g. Angus). A portion of the heifers are retained for
breeding and so maternal traits are of importance. The steers and surplus heifers are destined
for slaughter at 20 to 22 months of age.
Steers produce 300 kg carcases with 10 mm of P8 fat depth, while heifers
produce 270 kg carcases with 12 mm of P8 fat depth. A moderate cost is applied for cow feed costs
during the annual feed shortage period.
Northern Baldy
Terminal Index - Estimates the genetic differences between animals
in net profitability per cow joined in a commercial crossbred herd (e.g.
flatback) using Hereford bulls over Bos indicus/Tropical females (e.g. Santa
Gertrudis) where all progeny (male and female) are destined for slaughter. Steers and heifers are slaughtered at 20 to
22 months of age. Steers produce 340 kg
carcases with 14 mm of P8 fat depth while heifers produce 300 kg carcases with
17 mm of P8 fat depth.
Note that $Index values for
individual animals are sensitive to the assumptions used in the BreedObject
analysis to calculate the selection index.
More information is available on the weightings used in the Hereford Selection Indices.
Accuracy (%) is based on the amount of performance information
available on the animal and its close relatives - particularly the number of
progeny analysed. Accuracy is also based
on the heritability of the trait and the genetic correlations with other
recorded traits. Hence accuracy
indicates the "confidence level" of the EBV. The higher the accuracy value the lower the
likelihood of change in the animal's EBV as more information is analysed for
that animal or its relatives. Even
though an EBV with a low accuracy may change in the future, it is still the
best estimate of an animal's genetic merit for that trait. As more information becomes available, an EBV
is just as likely to increase in value, as it is to decrease.
Accuracy values range from
0-99%. The following guide is given for interpreting accuracy:
|
Accuracy
range |
Interpretation |
|
less
than 50% |
EBV
should be considered as a preliminary estimate. It could change substantially as more
performance information becomes available. |
|
50-74% |
Medium
accuracy, usually based on the animal's own records and pedigree. Still subject to substantial changes with more
information, particularly when the performance of progeny are analysed. |
|
75-90% |
Medium
- high accuracy and includes some progeny information. Becoming a more reliable indicator of the
animal's value as a parent. |
|
more
than 90% |
High
accuracy estimate of the animal's true breeding value. It is unlikely that the EBV will change
much with the addition of more progeny data. |
As a rule, animals should be
compared on EBVs regardless of accuracy.
However, where two animals have similar EBVs the one with higher
accuracy could be the safer choice, assuming other factors are equal. More information on accuracy is available from the BREEDPLAN Help Centre.
For further information please
contact the Herefords Australia Limited or
Hereford BREEDPLAN
Acknowledgments
and Disclaimer
BREEDPLAN
results are calculated using the beef genetic evaluation analytical software
developed by the Animal
Genetics and Breeding Unit and Meat & Livestock
Australia Limited.
Information
analysed in BREEDPLAN evaluations, including but not limited to pedigree,
performance and DNA information, is based on data supplied by clients and/or
third parties. The Agricultural
Business Research Institute (ABRI) does not oversee or audit the collection
of the data. Whilst every effort is made
to ensure the accuracy of the information, the ABRI, their officers and
employees assume no responsibility for its content, use or interpretation.
Estimated
Breeding Values can only be directly compared to other EBVs calculated in the
same analysis.