Aerobic performance

The PDK4 gene 
This horse’s result
GG
Ideal result for endurance
GG
i

Result summary

This horse has a gene variant that enhances aerobic metabolism over long distances.

Why this is important for Anglo-Arabians

For a horse to be registered as an Anglo-Arabian, it must have only thoroughbred and Arabian parentage.

An Anglo-Arabian can be 50% Arabian and 50% thoroughbred, 75% thoroughbred and 25% Arabian, or 75% Arabian and 25% thoroughbred. The PDK4 gene result can be different with each horse and is dependent on the genetic makeup of each parent/breed.

Anglo-Arabian horses with the PDK4 GG result have more type 1 muscle fibers than other horses. This is advantageous for endurance as the horse has greater aerobic power over longer distances, a lower heart rate, and resistance to muscle fatigue.

The PDK4 gene is responsible for Anglo-Arabian aerobic metabolism. Aerobic metabolism, the process of breaking down fuel stores in the body while exercising over long distances, is essential for endurance athletes. 

Oxygen is always present in a horse’s blood in restricted supplies, and these reserves can only produce limited amounts of energy (ATP) that lasts only a few seconds.  

Horses exercising at a moderate speed (trot, canter, or gallop) over longer distances need to move inhaled oxygen into their muscles and liver to convert carbohydrates and fats into energy for sustained muscle contraction. This is also essential for keeping heart rate low.

In contrast, some thoroughbreds inherit the PDK4 ‘A’ variant which provides them with short-term speed advantages. When these horses exercise, they mainly utilize anaerobic metabolism that is not dependent on oxygen to break down fuel stores but provides a rapid and limited supply of energy.

In endurance competitions, where stamina is valued as more important than short-term speed, the PDK4 ‘GG’ result is preferable to having an ‘A’ variant. A horse that inherits two PDK4 ‘G’ variants (GG) is genetically equipped to compete successfully over long-distances and in endurance competitions.

Horses with the PDK4 ‘A’ variant are genetically equipped to compete successfully over short, straight distances.

Future breeding implications

This horse has inherited one ‘G’ variant on the PDK4 gene from the sire and another ‘G’ variant from the dam. This gives the result PDK4 GG — one ‘G’ from each parent. Therefore, this horse will always pass one of these PDK4 ‘G’ variants to their foal.

However, a foal could inherit a ‘G’ variant (good for endurance) or an ‘A’ variant (not so good for endurance) from the other parent. Therefore, it is important to know the genetic results for both parents to understand all possible breeding implications.  

For example: 

GG (this horse) bred with another PDK4 GG horse (mate) =

  • 100% chance of the foal being a PDK4 GG horse.

Whereas:

GG (this horse) bred with a PDK4 AG horse (mate) =

  • 50% chance of a PDK4 GG foal.
  • 50% chance of a PDK4 AG foal.

How this gene influences endurance

A genetic variant in the PDK gene the ‘G’ variant, blocks the formation of three enzymes that make up the pyruvate dehydrogenase complex. This causes the oxidation of fat that then generates ATP to be used as energy in the skeletal muscles of the horse, giving the horse high aerobic capability. The use of fat to generate energy is important as it gives the horse more slow-burning energy, allowing the use of its muscles over an extended period, provided the speed and intensity of the training is not too high. 

In contrast, if the intensity of the exercise or training is too high, the horse will burn glycogen instead of fatty acids, resulting in muscle fatigue and poorer performance. Thus, pace and intensity are both important for optimal endurance performance.