Page 378 - The Veterinary Care of the Horse

surface but remains attached, the condition is known as osteochondritis dissecans.

Cyst-like lesions may develop in the bone just beneath the cartilage and some can
VetBooks.ir communicate with the joint surface through a defect in the articular cartilage. These are

subchondral bone cysts (see page 297).

Causes

Exactly how the disease develops is still poorly understood. It occurs as a result of a

combination of some of the following factors.

GROWTH RATE AND BODY SIZE

Studies suggest that in particular breeds such as Warmbloods, larger foals that grow rapidly

are more likely to develop OCD.

NUTRITION

• Overfeeding of high-energy diets to foals is associated with an increased occurrence of

OCD. It is thought that the high level of insulin produced to reduce the blood sugar level
has an adverse affect on the development of cartilage, possibly by suppressing the output

of thyroid hormones that influence normal cartilage development.
• Feeding excessively high levels of phosphorus or calcium is associated with an increased

incidence of OCD.
• Copper deficiency can result in a high incidence of OCD lesions in growing foals.

Attention should be paid to the copper levels in the diet of the pregnant mare as well as

that of the foal.
• Excessively high levels of zinc in the diet can interfere with copper uptake and lead to

OCD.

TRAUMA AND BIOMECHANICAL STRESS

Because OCD lesions occur in particular locations, it is likely that biomechanical factors play

a part in their development. They tend to develop in sites with high biomechanical loading
where the cartilage layer is relatively thick. Factors such as poor conformation, high body-

weight and inappropriate levels of exercise would have a direct influence on the forces
experienced in these areas.

However, this is not the whole story as the common sites for OCD in the equine hock are
not the areas with the thickest cartilage. Factors such as shearing forces and trauma may

damage the blood supply and contribute to the development of lesions.