Osteochondritis Dissecans (OCD) is a common developmental orthopedic disease involving the joints and cartilage of horses.

OCD typically develops during the first year of life and can lead to ongoing joint health issues. It is the leading cause of lameness and decreased performance in young athletic horses. [3]

In horses with this condition, the cartilage in joints doesn’t develop normally. This results in lesions in the cartilage and bone, potentially leading to the development of bone flaps or cartilage fragments that are free-floating within the joint.

Unfortunately, up to one-quarter of foals will have some form of OCD. It can affect any breed but is most commonly found in Standardbred, Thoroughbred, and Warmblood horses. [1][2]

Rapid growth and high-calorie diets are common causes of OCD. Imbalanced diets that do not provide adequate minerals may also increase the risk of this condition.

Fortunately, proper nutrition and management in the first two years of life can prevent or reduce the risk of your horse being affected by this condition.

What is OCD?

The term osteochondritis dissecans was first introduced by German surgeon Franz Konig in the 1800’s.

OCD is a developmental disorder that involves partial or total separation of a fragment of bone and cartilage from a joint (or articular surface). [24]

OCD can occur in any joint, but most frequently affects the hock, shoulder, stifle, and fetlock joints. Less commonly, OCD occurs in the elbow, hip, or even in the cervical vertebrae. [2]

It is most frequently diagnosed in young animals. [24] Research shows that horses with this condition do not form cartilage normally.

Cartilage

Cartilage is a frictionless surface that enables the smooth movement of joints. As the foal grows, a portion of new cartilage growth is remodelled into bone.

This process is known as endochondral ossification and it occurs at growth plates in the joints, at the end of long bones and during the healing of fractures.

In growing animals, the bones lengthen and epiphyseal cartilage is formed within the joints. However, in horses with OCD this process is disrupted, leading to lesions in the cartilage.

Effects of OCD

Affected joints develop irregular cartilage thickness and are weaker than normal joints. Over time, lesions can even detach from the bone and enter the joint capsule. This can lead to a more severe form of the disease and possible lameness. [2]

After OCD lesions appear on a joint, they will either heal spontaneously or evolve to a more advanced stage. If OCD lesions do not heal spontaneously, they can progress to calcification and bone remodelling. [6]

This can continue into adulthood and result in arthritis. [2]

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What Causes OCD in Horses?

Researchers have been studying OCD in horses for over 50 years. Originally, copper deficiency in the diet was believed to be the sole cause of equine OCD.

Studies show that adequate copper intake can help to repair OCD lesions, but dietary deficiency in this mineral is not the only factor that leads to OCD. [2]

OCD is now believed to be multi-factorial; several factors usually act together to cause the pathology. These factors include: [5]

  • Rapid growth rates
  • Blood flow problems
  • Lack of movement
  • Mineral deficiencies in the diet
  • Diets that are too high in energy
  • Trauma (including routine exercise)
  • Genetics

Excess Energy Intake

High-calorie diets are associated with an increased risk of rapid growth, cartilage problems and OCD.

Diets that contain excess digestible energy from sugar and starch raise levels of growth hormones.

Overfeeding is associated with higher levels of insulin and the growth factor IGF-1, which can affect the cells that make cartilage. There may also be changes in thyroid hormone levels, which can affect bone growth. [2]

In a study, foals were fed a diet to intentionally oversupply calories at 129% of their requirement for 16 weeks. They developed dyschondroplasia, which is a general term for abnormal cartilage. [16]

Nutrient Deficiency

Zinc and copper are important minerals that support healthy growth and cartilage formation. [15]

In 1988, a study showed that foals raised on diets that are severely deficient in copper develop joint abnormalities and stilted gaits.