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, Limousin 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 % Dir = 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
Artificial Insemination and hand mating records. Lower (negative) Gestation Length 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.
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
Eye Muscle Area EBVs are expected to produce better muscled and higher
percentage yielding progeny at the same carcase weight than will sires with
lower Eye Muscle Area 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 (marbling) at the 12/13th rib
site in a 300 kg carcase. Depending on market
targets, larger more positive values are generally more favourable.
Docility EBV
(%) is calculated from docility scores taken
at weaning or shortly afterwards. This
EBV is an estimate of the genetic difference in the percentage of progeny that
will be scored as docile or restless (scores 1 or 2).
Index values are reported as EBVs, in units of relative earning capacity ($) 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.
The Index values are derived
using BreedObject technology. More
information is available from the BreedObject web site.
Limousin selection indices are calculated for three production systems, namely, Domestic Maternal, Export Maternal, Northern Export and Yearling Prime. More information on the indexes is available in the Help Centre on the BREEDPLAN website.
Domestic Maternal Index - Estimates the genetic differences between animals in net profitability per cow joined for a typical self-replacing commercial herd targeting the domestic supermarket trade. Selected heifers are retained for breeding and so maternal traits are of importance. Steers and surplus heifers are finished on grass or a short fed grain program. Steers target 450 kg live weight (250 kg carcase weight & 8 mm P8 fat) and heifers 425 kg (235 kg carcase weight & 9 mm fat depth), at 15 months of age. In response to industry feedback, positive emphasis has been placed on the ability to meet MSA specifications.
Export Maternal Index - Estimates the genetic differences between animals in net profitability per cow joined for a typical self-replacing commercial herd targeting the heavy export trade. Selected heifers are retained for breeding and so maternal traits are of importance. Steers and surplus heifers are finished on grass or a short fed grain program. Steers target 560 kg live weight (330 kg carcase weight & 12 mm P8 fat) and heifers 525 kg (290 kg carcase weight & 14 mm fat depth), at 22 months of age. In response to industry feedback, positive emphasis has been placed on the ability to meet MSA specifications.
Northern Export Index - Estimates the genetic differences between animals in net profitability per cow joined for a typical commercial herd where Limousin bulls are joined with Bos indicus cows in Northern Australia targeting the export trade. This index assumes all progeny will be finished on grass. At market, steers target 580 kg live weight (330 kg HSCW and 12 mm P8 fat depth) and heifers 545 kg (300 kg HSCW and 14 mm P8 fat depth) at 27 months of age. In response to industry feedback, positive emphasis has been placed on finishing ability. This index can also be used by producers in Temperate Australia that are targeting larger carcase weights.
Yearling Prime Index - Estimates the genetic differences
between animals in net profitability per cow joined for a typical commercial
herd where Limousin bulls are joined with either British breed or dairy cows
and targeting the domestic carcase trade.
This index targets 365 kg live weight (200 kg HSCW and 5 mm P8 fat
depth) progeny. In response to industry
feedback, positive emphasis has been placed on the ability to meet MSA
specifications.
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 Limousin Society or Limousin
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.