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, Brahman 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 (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 visually acceptable.
EBVs are published for a range
of traits covering fertility, milking ability, growth, and carcase merit.
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.
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
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 12/13-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.
Percent Normal Sperm EBV (%) provides an estimate of genetic differences in percent
normal sperm, calculated from measurements taken as part of the bull breeding
soundness evaluation (BBSE) at around two years of age. It is expected that the sires with higher (ie
more positive) PNS EBVs will produce sons with higher PNS compared to sires
with lower (ie more negative) PNS EBVs.
Flight Time
EBV (secs) provides an estimate of genetic
differences between animals in temperament.
Flight Time EBVs are expressed as differences in the number of seconds
taken for an animal to travel approximately 2.0 metres after leaving the crush. Higher (ie longer) EBVs are more favourable,
indicating relatively longer time taken to exit the crush and hence relatively
better temperament.
Shear Force
EBV (kgs) provides an estimate of genetic
differences between animals in meat tenderness.
Shear Force EBVs are expressed as kilograms of shear force that are
required to pull a mechanical blade through a piece of cooked meat. Lower, more negative, EBVs are more
favourable, indicating that relatively less shear force is required, and hence
that the meat is more tender.
More information is available
on BREEDPLAN traits and data on the BREEDPLAN
website.
Brahman selection indices relate
to typical self-replacing Brahman commercial herds in tropical Australia.
Index values are reported as
EBVs, in units of relative earning capacity ($’s) for a given market. They reflect both the short-term profit
generated by a sire through the sale of his progeny, and the longer-term profit
generated by his daughters in a self-replacing cow herd. A selection index combines the EBVs with
economic information (costs and returns) for specific market and production
systems to rank animals based on relative profit values. Note that different types of animals can give
similar profit values, so consideration should be given to both the index and
the component EBVs when selecting animals for a particular production
system. More information is available on
using a selection index.
The Index values are derived
using BreedObject technology. More
information is available from the BreedObject web site.
Production
Index ($) - Estimates
the genetic differences between animals in net profitability per cow joined for
a typical self-replacing commercial herd targeting pasture finished
steers. Selected heifers are retained
for breeding and so maternal traits are of importance. Steers target 580 kg live weight (315 kg
carcase weight and 10 mm P8 fat depth) at 27 months of age, and heifers 470 kg
live weight (250 kg carcase weight and 12 mm P8 fat depth) at 25 months of age.
Live Export
Index ($) - Estimates
the genetic differences between animals in net profitability per cow joined for
a typical self-replacing commercial herd (tropical environment) targeting steers
for the live export markets. Steers are
assumed to be marketed to the live export agencies at 300 kg live weight and
then slaughtered after 120 days feedlot finishing at 470 kg live weight (255 kg
carcase weight).
Note that $Index Values for
individual animals are sensitive to the assumptions used in the BreedObject
analysis used to calculate the selection index.
More information is available on the weightings used in the Brahman 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% |
Low
accuracy. EBVs are preliminary and
could change substantially as more performance information becomes available. |
|
50-74% |
Medium
accuracy, usually based on the animal's own records and pedigree. |
|
75-90% |
Medium-high
accuracy. Some progeny information included. EBVs may change with addition of more
progeny data. |
|
more
than 90% |
High accuracy
estimate of the animal's true breeding value. |
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.
For further information please
contact the Brahman Association or Brahman
BREEDPLAN
BREEDPLAN and GROUP BREEDPLAN
results are calculated using software developed by the Animal Genetics and
Breeding Unit, a joint venture of NSW Department of Primary Industries and the
University of New England, which receives funding for this purpose from Meat
and Livestock Australia Limited.