Morphological genetic indices or characterization

What is a morphological genetic index ?

Genetic indices, for each of the characteristics studied, enable us to sum up the reproductive qualities of a horse with a figure. They are useful for the following :

To compare a horse to others
To rationalize mating
To select horses for reproduction : approving stallions, allocation of endowments, supporting breeding

Morphological genetic indices have been established for more and more different breeds : Selle Français , Cob Normand , Comtois draught horse and Haflinger. They are based on markers/ judgements made during showing competitions.

Understanding genectic indices

How they are established

Each genectic index is related to a given breed. They are calculated on average every three years, and take into account all the information pertaining to a specific horse and to its kindred (forebearers, descendants, collaterals)

Expressing genetic indices

The indices are calculated in relation to a reference group of horses so as to define level zero. For morphological indices, it refers to the selected population for the breed considered, over a given period, or for a given age.
There are two types of morphological genetic index :

Those coming from judgement marks
Those coming from markers.

The former are established in the same way as sport performance genetic indices. The more positive the mark, the better the horse will be considered as « improver » for the studied characteristic.
The latter work a little differently. A positive indice is not necessarily « improver ». It is based on the optimum for the trait studied , the reproducer is then either rated as « improver » or « deteriorater » for the breed considered.

Determination coefficient of genetic indices.

The determination coefficient (noted DC) is always associated to the index. It shows the accuracy with which the genetic index was assessed. The value is between 0 and 1. The more information is available, the closer the DC is to 1.
Thr determination coefficient can increase through a reproducer’s lifetime, as more information becomes available.
Depending on the breed, there is a unique DC per horse (Ardennais draught horse, Norman Cob) or there is a DC per criteria, and per horse (Comtois draught horse, haflinger).

Evolution of morphological genetic indices

Whenever there is an update, the genetic index of a horse evolves :

On the one hand, thanks to availability of new information. Depending on the said information, a horse’s genetic index may evolve positively or negativeley.
On the other hand, due to the comparison between the subject and the mobile basis. In effect, with time, the conformation of a population of horses increases thanks to selective breeding. Thus the genetic worth of a reproducer tends to decrease with age.

The genetic index of a horse therefore evolves over time. Only the latest genetic index is published, as it more reliable and accurate than previous ones (it has the highest DC).

Using morphological genetic indices

By definition, a genetic index is the best tool available for rationalizing mating, with the purpose of producing horses which best meet the optimum criteria for the breed. It is the best estimation of the quality as a progenitor of the horse, according to available information. The indices are available for approved stallions.
But be careful : the accuracy is never 100 % (DC=1). Thus, there is a certain probability that the genetic worth of the horse could be above or below the estimated genetic index.

Example of indexation of a Haflinger stallion.