Page 6 - Ariki 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, NZ
ANGUS 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

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