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, Murray Grey BREEDPLAN EBVs cannot be validly compared with
EBVs from any other BREEDPLAN analysis.
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.
Gestation
Length EBV (days)
provides an estimate of genetic differences between animals in gestation
length. Lower or more negative Gestation
Length EBVs are considered to be more favourable.
Birth Weight
EBV (kg) provides an estimate of genetic
differences between animals in calf birth weight. Small or moderate Birth Weight EBVs are more
favourable. 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) provides an
estimate of genetic differences between animals in live weight at 200 days of
age due to their genetics for growth.
Larger, more positive 200 Day Growth EBVs are generally more
favourable. This EBV is the best single
estimate of an animal's genetic merit for growth to early ages.
400-Day Weight
EBV (kg) provides an
estimate of genetic differences between animals in live weight at 400 days of
age. This EBV is important for breeders
turning off animals as yearlings.
Larger, more positive 400 Day Weight EBVs are generally more favourable.
600-Day Weight
EBV (kg) provides an
estimate of genetic differences between animals in live weight at 600 days of
age. This EBV is important for breeders
targeting the production of animals suited for heavy weight grass or grain fed
markets. Larger, more positive 600 Day
Weight EBVs are generally more favourable.
Mature Cow
Weight EBV (kg) provides an estimate of genetic
differences between cows in live weight at 5 years of age. This EBV is an indicator of growth at later
ages and potential feed maintenance requirements of the females in the breeding
herd.
Milk EBV (kg) provides an estimate of maternal genetic contribution
of a dam to the 200 day weight of her calf. In the case of sires, this EBV estimates the
maternal genetic effect that his daughters will contribute to the 200 day weight of their progeny. Larger, more positive, Milk EBVs indicate a
greater maternal genetic contribution to 200 day
weight.
Scrotal Size
EBV (cm) provides an estimate of genetic
differences between animals in scrotal circumference at 400 days of age. Larger, more positive, Scrotal Size EBVs
indicate are generally more favourable.
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) provides an estimate of genetic
differences in fertility of the daughters of the sire. It is the time interval between the date when
the female is first exposed to a bull in a paddock mating to the day when she
subsequently calves. Relatively lower
EBVs for days to calving indicate shorter interval from bull-in date to calving
and therefore higher fertility.
Carcase Weight
EBV (kg) provides an estimate of genetic
differences between animals in carcase weight at the standard age of 650
days. Larger, more positive Carcase
Weights EBVS are generally more favourable.
The Carcase Weight EBV is an indication of the animal’s carcase weight
and not an indication of the animal’s yield percentage.
Eye Muscle
Area EBV (sq cm)
provides an estimate of genetic differences between animals in eye muscle areas
at 12/13th rib site of a 300 kg dressed steer carcase. More positive EBVs indicate better muscling
on animals. Animals with relatively
higher EMA EBVs are expected to produce better muscled and higher percentage
yielding progeny at the same carcase weight than will animals with lower EMA
EBVs.
Rib Fat and
Rump Fat EBVs (mm)
provide estimates of genetic differences between animals in subcutaneous fat
depth at the 12/13th rib site and the P8 rump site. Animals with relatively lower fat EBVs are
expected to produce leaner progeny at any particular carcase
weight than will animals with higher EBVs.
Retail Beef
Yield EBV (%) provides an estimate of genetic
differences between animals for retail yield percentage in a standard 300 kg
steer carcase. Animals 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 steer carcase.
Depending on market targets, larger more positive values are generally
more favourable.
Murray Grey selection indices
are calculated for five market specifications, namely, Vealer Terminal,
Supermarket, Heavy Grass Fed, Northern Terminal and
Breeder Replacement.
Index values are reported as
EBVs, in units of relative earning capacity ($’s) for a given market. They reflect both the short-term profit
generated by a sire through the sale of his progeny, and the longer-term profit
generated by his daughters in a self-replacing cow herd. A selection index combines the EBVs with
economic information (costs and returns) for specific market and production
systems to rank animals based on relative profit values. Note that different types of animals can give
similar profit values, so consideration should be given to both the index and
the component EBVs when selecting animals for a particular production
system. More information is available on
using a selection index.
The Index values are derived
using BreedObject technology. More
information is available from the BreedObject web site.
Vealer Terminal Index ($) - Estimates the genetic differences
between animals in net profitability per cow joined for a typical crossbred
commercial herd using Murray Grey bulls to target vealer production. Vealers
are finished on grass and target 430 kg live weight (225 kg HSCW and 9 mm P8
fat depth) at 12 months of age. Daughters are NOT retained for breeding and
thus no consideration is given to maternal traits.
Supermarket Index
($) - Estimates the genetic differences between animals in net profitability
per cow joined for a typical Murray Grey commercial herd targeting production
of steers for the domestic supermarket trade. Selected heifers are retained for
breeding and thus maternal traits are of importance. Steers are either finished
on grass, or grain fed for 70 days, and target 470 kg live weight (260 kg HSCW
and 12 mm P8 fat) at 15 months of age. In response to industry feedback a
premium has been placed on marbling.
Heavy Grass Fed Steer Index ($) - Estimates the genetic differences between animals in
net profitability per cow joined for a typical Murray Grey commercial herd
targeting pasture finished steers for heavier grass fed
markets. Selected heifers are retained for breeding and thus maternal traits
are of importance. Steers target 620 kg live weight (330
kg HSCW and 14 mm P8 fat depth) at 24 months of age. In response to
industry feedback a premium has been placed on marbling.
Northern Terminal Index
($) - Estimates the genetic differences between animals in net profitability
per cow joined for a typical commercial herd using Murray Grey bulls over cows
containing some Bos indicus content. Steers
target 550 kg live weight (300 kg HSCW and 10 mm P8 fat depth) at 27 months of
age. In response to industry feedback a premium has been placed on
marbling.
Breeder Replacement Index ($) - Estimates the genetic differences between animals in
net profitability per cow joined for a typical Murray Grey commercial herd
targeting the production of weaners or yearlings. Selected heifers are retained
for breeding and thus maternal traits are of importance. Steers target 440 kg
live weight (230 kg HSCW and 9 mm P8 fat depth) at 12 months of age.
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 Murray Grey
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.
Estimated Breeding Values
can only be directly compared to other EBVs calculated in the same analysis.
Whilst every effort is made
to ensure the accuracy of the information, the Agricultural Business Research
Institute, the Society, their officers, and employees assume no responsibility
for its content, use or interpretation.
BREEDPLAN results are calculated
using software developed by the Animal Genetics and Breeding Unit, a joint
venture of New South Wales Department of Primary Industries and the University
of New England, which receives funding for this purpose from Meat and Livestock
Australia Limited.
For further information please
contact the Murray Grey Society or Murray Grey BREEDPLAN