Page 9 - Brackenfield Angus Catalogue ebook
P. 9
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
Brackenfield Angus “above or below breed average” for a particular trait.
Whilst EBVs provide the best basis for the comparison of the genetic
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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.
ANGUS 9