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.
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 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) 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.
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) 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. 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 (%)
indicates genetic differences between animals for retail yield percentage in a
standard 300 kg carcase. Animals with
larger EBVs are expected to produce progeny with higher yielding carcases.
Flight Time (Trial) EBV (secs)
indicates genetic differences between animals in temperament. Trial 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 (Trial) EBV (kgs)
indicates genetic differences between animals in meat tenderness. Trial 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.
A Brahman selection index is calculated for
the grass-finished Jap Ox market. It
relates to typical self-replacing Brahman herds in tropical
Index values are reported as EBVs, in units
of relative earning capacity ($’s) for a given market. They reflect both the short-term profit
generated by a sire through the sale of his progeny, and the longer-term profit
generated by his daughters in a self-replacing cow herd. A selection index combines the EBVs with
economic information (costs and returns) for specific market and production
systems to rank animals based on relative profit values. Note that different types of animals can give
similar profit values, so consideration should be given to both the index and
the component EBVs when selecting animals for a particular production
system. More information is available on
selecting animals using a selection index.
The Index values are derived using
BreedObject technology. More information
is available from the BreedObject web site.
Jap Ox Index ($) - Estimates the genetic differences between
animals in net profitability per cow joined for an example commercial herd
targeting steers for Export markets. Steers
are assumed to be pasture grown & finished, weighing 600 kg live weight or
325 kg carcase weight at 32 months from a self-replacing herd run in a tropical
environment. Daughters are retained in
the industry for breeding.
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 Jap Ox Index.
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