Page 7 - Kaingaroa Simmentals 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, Simmental
BREEDPLAN EBVs cannot be validly compared with EBVs for any other breed.
EBVs are published for a range of traits covering fertility, calving ease, milking ability,
growth, and carcase merit. 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 % Dir = 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.
Kaingaroa Simmentals • 5