Page 5 - Blenheim 2021 Catalogue ebook

EBVS EXPLAINED

UNDERSTANDING THE EBVS,
SELECTION INDEXES AND ACCURACY EBVS
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, TACE 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.

BLENHEIM BULL SALE
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