Genetic and performance horse indices

Performance index

A horse’s performance index, is the summary of the results achieved by the horse in racing or equestrian sports competitions, over a given period. A corrective factor is then applied, this takes into account variations due to the environment : year, sex, age, and, in some cases rider or trainer...

Performance index= performances measured – Environmental effects

The performance index ranks a horse in relation to its contemporaries.

Example of a corrective factor : age in a show-jumper

In the population of 4 year old horses, some will be of equal quality to the population of 8 year-old horses. It appears therefore natural to give them an equivalent performance index. Whether aged 4 or aged 8, a horse with an index of 120, is ranked in the top 11 % of show-jumping horses. Even if the technical performances are not equivalent (a 4 year-old will have competed over easier courses than an 8 year-old), it is as difficult to obtain a high index, whatever the horse’s age.

Performance indices are used to :

Compare horses to each other
Assess the quality of a horse when buying it.

Only horses having competed in affiliated competitions have a performance index. Indices are calculated annually, and published in December of the year for Olympic disciplines, and at the beginning of the year in endurance racing.

Diagram showing how the index is calculated

It should also be noted :

Every year around 12 % of horses with an index (all horses having competed in affiliated shows) will reach at least a 120 index (« good horses »)
Every year around 1 to 2 % of horses with an index (all horses having competed in affiliated shows) will reach at least an index of 140 (« very good horses »)

The difference between two different indices can be explained by the regularity of results, the number of competitions taken part in, as well as the level of competition taken part in, and the horses competed against.

Accuracy coefficient

Since 1997, a coefficient of precision ( noted as CP ) has been attributed to each performance index. The CP depends on the number of participations in affiliated competitions, but also on the number of participants in each class. The CP is noted in brackets after the index.
The value of the CP is situated between 0 and 1, depending on the amount and quality of data available for each horse. The closer to 1 it is, the more precise the index it accompanies is (the higher the number of participations and participants).

Points of Reference for the CP in equestrian sports.

< 0,60 : index is not well known
Between 0,60 and 0,80 :Index is quite well known
≥ 0,80 : Index is known with certainty

If the CP is too low, the index is « non significant ». The information available for the horse is too scarce to calculate a reliable index.

Genetic index

The genetic index is established so as to assess the genetic qualities of a horse, i.e the capacity to pass on these qualities to the progeny. It enables to predict the worth of the stallion or mare’s production.

A genetic index is therefore useful :

To compare horses to each other
To think through the coupling of stallions and mares
To select the reproducers : stallion approval, encouraging breeders.

All horses from approved origins possess a genetic index. However not all indices are published, as they are sometimes deemed unreliable by the breed association. This is often because the coefficient of determination is not significant enough.
To calculate the genetic index, one could wait for performances of the horse’s progeny. But it is useful to have an idea of the genetic worth before choosing to have a mare covered, or to approve a stallion as a reproducer for the breed.
To obtain an estimation of the genetic worth of a horse, his own performances and the performances of all his related kin are used. All this information is balanced out and depends on the heritability and the degree of relation betweeen the horse assessed and the horse measured. When the progeny’s results are taken into account in determining the genetic worth, one must take care to use a representative range of the descendance, and not take into account only those descendants competing internationally for example.

Evolution of genetic indices

Every year, a horse’s genetic index will evolve according to new data available. Depending on the information, the index may evolve positively (e.g : a new excellent performance index) or negatively (e.g : progeny not performing well).
Thus a horse’s index will evolve over time. It is only the last index calculated which is published, as it is always more reliable and accurate than the previous ones (the CD is highest). Genetic indices are transferred to the progeny by halves :

BLUP foal= (BLUP sire + BLUP dam)/2
CD foal = (CD sire + CD dam )/4

The coefficient of determination

The coefficient of determination, (called CD) is always associated to a genetic index. It gives an indication as to the accuracy with which the gentic index was assessed. Its value is situated between 0 and 1. The more information is included, the closer the CD gets to 1. The CD can increase throughout the reproducer’s life as more data becomes available.

CD values are thus a result of the different types of data recorded