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 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.
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 the day 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.
Murray Grey selection indices are calculated
for three market specifications, namely, Long-Fed, Supermarket and Heavy Grass
Fed. These Indices relate to
typical self-replacing Murray Grey herds in temperate Australia targeting these
specifications.
Index values are reported as EBVs, in units
of relative earning capacity ($’s) for a given market. They reflect both the short-term profit
generated by a sire through the sale of his progeny, and the longer-term profit
generated by his daughters in a self-replacing cow herd. A selection index combines the EBVs
with economic information (costs and returns) for specific market and
production systems to rank animals based on relative profit values. Note that different types of animals
can give similar profit values, so consideration should be given to both the
index and the component EBVs when selecting animals for a particular production
system. More information is
available on selecting animals using a selection index.
The Index values are derived using
BreedObject technology. More
information is available from the BreedObject web site.
Long-Fed Index ($) - Estimates the genetic differences between
animals in net profitability per cow joined for an example commercial herd
targeting the production of steers for long-fed export markets such as the
Japanese B3 market. Steers are
pasture grown and then slaughtered at 22 months of age after 200 days on feed
(average 700 kg live weight).
Daughters are retained for breeding. There is a significant premium if steers reach a marble
score of 2 or greater.
Supermarket Index ($) - Estimates the genetic differences between
animals in net profitability per cow joined for an example commercial herd targeting
production of steers for the domestic supermarket trade. Steers are finished on either grass or
grain (eg 50 – 70 days) and then slaughtered at 17 months of age (average 455
kg live weight). Daughters are
retained for breeding. In response
to industry feedback regarding eating quality and tenderness, a small premium
has been placed on marbling.
Heavy Grass Fed Index ($) - Estimates the genetic differences between
animals in net profitability per cow joined for an example commercial herd
targeting pasture finished steers for heavier grass fed markets such as
Korea. Steers are assumed marketed
at 580 kg live weight (320 kg HSCW and 12 mm P8 fat) at 22 months of age. Daughters are retained for
breeding. In response to industry
feedback regarding eating quality and tenderness, a small premium has been
placed on marbling.
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.
For further information please contact the Murray
Grey Society or Murray Grey BREEDPLAN