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 positive or negative
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 +30 kg for 400-Day Weight is
estimated to have genetic merit 30 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. The breed averages for
the current two year old animals are reported with the selected animals’
EBVs.
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, British Charolais BREEDPLAN
EBVs cannot be validly compared with EBVs for any other breed.
EBVs
are published for a range of traits covering fertility, calving ease, 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.
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 a tendency for 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 200 days, 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
own 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 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.
Fat Depth EBV (mm) is calculated from measurements of subcutaneous
fat depth at the rib (from live animal ultrasound scans and from abattoir
carcases if available) and are adjusted to a standard
300 kg carcase. This EBV indicates the
genetic difference in fat distribution on a standard 300 kg carcase. Sires with a low, or negative, fat EBV 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.
The
British Charolais Cattle Society has developed two selection indices - the BCCS
Terminal Index and the BCCS Self Replacing Index. Based on the BREEDPLAN performance recording
technology, the indices are calculated for commercial cattle producers wishing
to produce slaughter progeny from larger framed cows. Each Index is reported as an EBV, in units of
relative earning capacity (£’s) per
cow mated for the given market, and reflects the potential profit generated by
a sire for the production system.
BCCS Terminal Index - Estimates the
genetic differences between animals in net profitability per cow mated for an
example commercial herd targeting the EU market with no marbling
requirement. All progeny are assumed to
be marketed at approximately 18 months of age with steers being around 680 kg
live weight and heifers around 625 kg after finishing with extra supplements.
As
the name suggests, this index ranks bulls by their genetic potential for the
production of prime steers and heifers for beef production. Consequently, growth and carcase EBV’s are the main drivers used in compiling this
Index while some emphasis is also placed on calving ease direct, which is an
estimate of genetic difference between animals ability to calve without
assistance.
Bulls
with a higher BCCS Terminal Index will have a greater genetic potential to sire
heavier finished progeny. As there are
no maternal traits included in the calculation of the BCCS Terminal Index,
bulls with a high Index will not necessarily be suitable for breeding heifer
replacements.
BCCS Self Replacing Index -
Estimates the genetic differences between animals in net profitability per cow
mated for an example commercial herd producing steers to turn off at approximately
16 months of age. Replacement females
are selected from within the herd. There
is some emphasis on calving ease and maternal traits while finishing steers at
around 680kg (375 kg carcase weight) using a pasture based production system.
This index
is also suited to Stud herds and herds using Charolais sirese
over mixed breed cows where femaole replacements are
sourced from within the herd.
Typical
production parameters, prices and costs underlay these selection Indices.
Benefits and costs evaluated include both those for the sale animal from birth
to slaughter and average running costs for a typical cow herd. Feed is assumed a limited resource for a
large part of the year and any increase in feed requirement is a cost.
The
Indices are derived using BreedObject
technology. More information is
available from the BreedObject web
site.
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 relationships (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, there
is an equal likelihood that an EBV will 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 British Charolais Cattle
Society