Page 90 - 2021 Rangatira Bulls

NZ ANGUS BREEDPLAN
Understanding the EBVs, Selection Indices and Accuracy

EBVs Carcase Weight EBV (kg) is based on abattoir carcase records and is an indicator of
An animal’s breeding value is its genetic merit, half of which will be passed on to its the genetic differences in carcase weight at the standard age of 750 days.
progeny. While we will never know the exact breeding value, for performance traits it Eye Muscle Area EBV (sq cm) is calculated from measurements from live animal
is possible to make good estimates. These estimates are called Estimated Breeding ultrasound scans and from abattoir carcase data, adjusted to a standard 400 kg carcase.
Values (EBVs). This EBV estimates genetic differences in eye muscle area at the 12/13th rib site of a
In the calculation of EBVs, the performance of individual animals within a contemporary 400 kg dressed carcase. More positive EBVs indicate better muscling on animals. Sires
group is directly compared to the average of other animals in that group. A with relatively higher EMA EBVs are expected to produce better-muscled and higher
contemporary group consists of animals of the same sex and age class within a herd, percentage yielding progeny at the same carcase weight than will sires with lower EMA
run under the same management conditions and treated equally. Indirect comparisons EBVs.
are made between animals reared in different contemporary groups, through the use of Rib Fat and Rump Fat EBVs (mm) are calculated from measurements of subcutaneous
pedigree links between the groups. fat depth at the 12/13-rib site and the P8 rump site (from live animal ultrasound scans
EBVs are expressed in the units of measurement for each particular trait. They are and from abattoir carcases) and are adjusted to a standard 400 kg carcase. These EBVs
shown as + ive or - ive differences between an individual animal’s genetics difference are indicators of the genetic differences in fat distribution on a standard 400 kg carcase.
and the genetic base to which the animal is compared. For example, a bull with an EBV Sires with low, or negative, fat EBVs are expected to produce leaner progeny at any
of +50 kg for 600-Day Weight is estimated to have genetic merit 50 kg above the breed particular carcase weight than will sires with higher EBVs.
base of 0 kg. Since the breed base is set to an historical benchmark, the average EBVs Retail Beef Yield EBV (%) indicates genetic differences between animals for retail
of animals in each year drop has changed over time as a result of genetic progress yield percentage in a standard 400 kg carcase. Sires with larger EBVs are expected to
within the breed. produce progeny with higher yielding carcases.
The absolute value of any EBV is not critical, but rather the differences in EBVs between Intramuscular Fat EBV (%) is an estimate of the genetic difference in the percentage
animals. Particular animals should be viewed as being “above or below breed average” of intramuscular fat at the 12/13th rib site in a 400 kg carcase. Depending on market
for a particular trait. targets, larger more positive values are generally more favourable.
Whilst EBVs provide the best basis for the comparison of the genetic merit of animals Docility EBV (%) is an estimate of the genetic differences between animals in
reared in different environments and management conditions, they can only be used temperament. Docility EBVs are expressed as differences in the percentage of progeny
to compare animals analysed within the same analysis. Consequently, NZ ANGUS that will be scored with acceptable temperament (ie. either “docile” or “restless”).
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 Selection Indices
traits, they do not provide information for all of the traits that must be considered during There are currently two different selection indexes calculated for New Zealand Angus
selection of functional animals. In all situations, EBVs should be used in conjunction animals. These are Self-Replacing and AngusPure. Each selection index describes a
with visual assessment for other traits of importance (such as structural soundness, different production/market scenario and relates to a typical commercial herd in New
temperament, fertility etc). A recommended practice is to firstly select breeding stock Zealand that is targeting the following specifications.
based on EBVs and to then select from this group to ensure that the final selections are Index values are reported as EBVs, in units of relative earning capacity ($’s) for a given
otherwise acceptable. market. They reflect both the short-term profit generated by a sire through the sale of his
EBVs are published for a range of traits covering fertility, calving ease, milking ability, progeny, and the longer-term profit generated by his daughters in a self-replacing cow
growth, carcase merit and feed efficiency. When using EBVs to assist in selection herd. More information is available on selecting animals using a selection index.
decisions it is important to achieve a balance between the different groups of traits and The Index values are derived using BreedObject technology. More information is
to place emphasis on those traits that are important to the particular herd, markets and available from the BreedObject web site.
environment. One of the advantages of having a comprehensive range of EBVs is that
it is possible to avoid extremes in particular traits and select for animals with balanced Self-Replacing Index ($) - Estimates genetic differences between animals in net
overall performance. profitability per cow joined for a self-replacing commercial herd, targeting the production
of grass finished steers. Steers are assumed marketed at 525 kg live weight (280 kg
Calving Ease EBVs (%) are based on calving difficulty scores, birth weights and carcase weight and 10 mm fat depth) at 16 months of age.
gestation length information. More positive EBVs are favourable and indicate easier
calving. AngusPure Index ($) – Estimates genetic differences between animals in net
profitability per cow joined for a self-replacing commercial Angus herd, targeting the
CE % Direct = Direct Calving Ease - The EBV for direct calving ease indicates production of grass finished steers for the AngusPure programme. Steers are assumed
the influence of the sire on calving ease in purebred females calving at two years marketed at 525 kg live weight (280 kg carcase weight and 10 mm fat depth) at 18
of age. months of age with a significant premium paid for marbling.
CE % Daughters = Daughters’ Calving Ease - The EBV for daughters’ calving Note that $Index values for individual animals are sensitive to the assumptions used in
ease indicates how easily that sire’s daughters will calve at two years of age. the BreedObject analysis to calculate the selection index. More information is available
on the weightings used in the New Zealand Angus Selection Indices.
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 Accuracy
shorter gestation length and therefore easier calving and increased growth after birth. Accuracy (%) is based on the amount of performance information available on the
Birth Weight EBV (kg) is based on the measured birth weight of progeny, adjusted for animal and its close relatives - particularly the number of progeny analysed. Accuracy
dam age. The lower the value, the lighter the calf at birth and the lower the likelihood of is also based on the heritability of the trait and the genetic correlations with other
a difficult birth. This is particularly important when selecting sires for use over heifers. 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
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 information is analysed for that animal or its relatives. Even though an EBV with a low
the best single estimate of an animal’s genetic merit for growth to early ages. 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
400-Day Weight EBV (kg) is calculated from the weight of progeny taken between 301 increase in value, as it is to decrease.
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. Accuracy values range from 0-99%. The following guide is given for interpreting
accuracy:
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 Accuracy range Interpretation
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 less than 50% EBV should be considered as a preliminary estimate.
weaning, adjusted to 5 years of age. This EBV is an estimate of the genetic difference It could change substantially as more performance
in cow weight at 5 years of age and is an indicator of growth at later ages and potential information becomes available.
feed maintenance requirements of the females in the breeding herd. Steer breeders 50-74% Medium accuracy, usually based on the animal’s own
wishing to grow animals out to a larger weight may also use the Mature Cow Weight records and pedigree. Still subject to substantial changes
EBV. with more information, particularly when the performance of
Milk EBV (kg) is an estimate of an animal’s milking ability. For sires, this EBV indicates progeny are analysed.
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. 75-90% Medium - high accuracy and includes some progeny
information. Becoming a more reliable indicator of the
Scrotal Size EBV (cm) is calculated from the circumference of the scrotum taken animal’s value as a parent.
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 more than 90% High accuracy estimate of the animal’s true breeding
correlation with age of puberty in female progeny and therefore selection for increased value. It is unlikely that the EBV will change much with the
scrotal size will result in reduced age at calving of female progeny. addition of more progeny data.
Days to Calving EBV (days) indicates the fertility of the daughters of the sire. It is the As a rule, animals should be compared on EBVs regardless of accuracy. However,
time interval between the day when the female is first exposed to a bull in a paddock where two animals have similar EBVs the one with higher accuracy could be the safer
mating to the day when she subsequently calves. A negative EBV for days to calving choice, assuming other factors are equal.
indicates a shorter interval from bull-in date to calving and therefore higher fertility.
For further information please contact NZ Angus or BREEDPLAN.

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