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 are
called Estimated Breeding Values (EBVs).
They are expressed as the difference between an individual animal's
genetics and the genetic base to which the animal is compared.
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 the date 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. 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 low, or negative, 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.
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.
A
Brahman selection index is calculated for the grass-finished Jap Ox market with
a target age of 32 months. It
relates to typical self-replacing Brahman herds in tropical Australia targeting
Jap Ox specifications.
Indexes
are reported as an EBV, in units of relative earning capacity ($’s) for a given
market. They reflect both the
short-term profit generated by a sire through the sale of his progeny, and the
longer term profit generated by his daughters in a sustainable cow herd.
The Index is derived using the BreedObject technology. For more information about this
technology go to the BreedObject web
site
Jap
Ox Index ($) - Estimates the genetic differences between animals in
net profitability per cow joined for an example commercial herd targeting
pasture finished 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 it's relatives.
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