What is an EBV and how is it calculated?
An Estimated Breeding Value (EBV) or Breeding Value (BV) is an estimate of how a particular animal is going to perform as a parent. Because parents only pass their genes onto their offspring and not the effects of the environment, EBVs are an estimate of only the genetic part of the difference in performance between animals. The percentage of this genetic part of the difference in performance is known as the heritability or the strength of the genetic influence in a particular trait.
The Performance resulting from the activities of genes.
The total performance (resulting from gene activity +environmental effects)
Heritability estimates have been determined by scientific research and are being refined continuously.
A basic within-group EBV is calculated by running a group of animals, of roughly the same age and sex, together under exactly the same conditions (environment) for a period of time, during which measurements are taken on each animal. These measurements may include weights at birth, 200, 400 and 600 days of age, fat depths, eye muscle areas and scrotal size.
These measurements are adjusted by the computer to put all animals in the group on the same ‘level playing field’. For example, they have to be adjusted to the same age to give a fair comparison. The average measurement for the group is then worked out, and then the amount by which each individual within the group differs from that average. This figure is then multiplied by the heritability of the trait (as we are only interested in the genetic part of the performance) and this gives the EBV for a particular animal and trait.
Calculation of a simple within -group EBV
The adjusted 400 day weight for animal ‘X’ is 380 kgs., compared with the average for its group of 350 kgs. There is no information on its relatives. The heritability for 400-day weight is 0.3 or 30%. i.e. 30% of the measured performance difference between animals is the result of the activities of the genes which control 400 day weight, and will be passed on to the offspring.
|Animal X’s 400-Day Wt. EBV=.
(adjusted wt. of X – average adjusted wt. of the group) x heritability for 400 Day Wt.
=(380 kgs. Ð 350 kgs.) x 0.3 kgs.
= 30kgs. x 0.3 kgs.
= 9 kgs.
This is the simplest form of an EBV using information on the animal’s own performance. Modern genetic evaluation systems use information on relatives and the effects of related traits to make the EBV more accurate.