Page 10 - Waimara 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,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.
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 (negative) GL EBVs indicate shorter
gestation length and therefore easier calving and increased growth after birth.

8 Waimãra Angus