Page 7 - Nethertown Angus Catalogue ebook

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 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 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.
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
Nethertown Angus 5