Injury risk

The results


This horse has a slightly higher risk of occurring a stress fracture during training or racing.

In most cases, a horse’s body can repair tiny microfractures by reinforcing and remodeling the bone matrix so it can better cope with stress. If a horse is not given enough time to heal, fractures can reoccur or worsen.

Horses with this genotype have bulky, round muscles, that lack flexibility and are susceptible to tiny muscle tears and soreness, especially if worked without prior stretching or while fatigued.


58% of injuries in young racehorses are stress fractures.

Injury in racehorses is usually the result of either external or internal forces.

External forces being single violent incidents, such as falls, kicks or collisions, while internal forces are usually caused by speed or fatigue during racing or training.

Identifying genetic markers that present a higher risk of injury in thoroughbreds can allow breeders to make informed decisions to reduce the probability of breeding at risk foals and improve future generations of thoroughbreds.

A known genetic influence on fracture risk and muscular injury in horses is the MTSN mutation.

While management, nutrition, training decisions and genetics all play their part, understanding fracture risk can help guide training and management decisions.

Injury risk considerations

Stress fractures are often misdiagnosed, and complications can develop when horses with unrecognized microfractures are trained hard or raced. Injury is one of the principal causes of retirement from racing and lost racing days.

Muscle: All equine movements, from the swish of a tail to the rapid action of a gallop, are brought about by a complicated system of skeletal muscles. Although the composition of muscle fiber type is controlled by genetic makeup, training can alter the proportions, at least to a limited extent. Skeletal muscles always have the potential to adapt during training and can positively influence stamina, strength, and speed.

Bone: Thoroughbreds are at an increased risk of stress fractures within the first 12 months of racing and when resuming training after a break. These injuries, which are characterized by pain and lameness and an unwillingness to work at speed are a common response to exercise stress.

The genetic details

The MSTN mutation signifying a higher risk for bone fracture and muscle injury is inherited from both dam and sire.

The mutation doesn’t directly cause injury. Rather, it increases overall weight to wither height ratio, heightening the chance of a fracture or muscle tear during training.

Providing the parent horse has the mutation, one mutated gene can be passed by each parent to their foal. As your horse has two copies of the mutation, one from each parent, it has inherited an above average risk for a training injury.