A part of the collection of conditions which make up Developmental Orthopaedic Disease, OCD is a common disorder of cartilage growth and maturation in animals and humans. It occurs in all domestic species and has been noted in rapidly growing wild animals like Giraffe. The prevalence amongst Thoroughbred horses on Australian stud farms was of the order of 26% in one study which is compatible with rates in other countries.
The disease results from failure of normal growth, maturation, and ossification of the cartilage matrix around which bones are formed. It occurs at several predilection sites around the skeleton, principally at the ends of long bones, the bones of the knee and hock, and cervical vertebrae.
Focal lesions and defects in the articular cartilage in joints develop alongside healthy cartilage. The underlying boney columns supporting the cartilage may collapse or degenerate leaving pits similar to ulcerated depressions in the cartilage covering of the bone. In some cases, fragments of cartilage may separate and float free in the joint, these are visible as so called ‘’joint mice’’ on X-Rays and distinguish true OCD from osteochondrosis.
Lesions may be present at birth, but most develop during the first five months of life and rarely thereafter. Many lesions will resolve spontaneously by 12 months of age, but some will require surgical intervention.
The cause of Osteochondrosis is multifactorial with genetic predisposition likely but contributing factors including in particular rapid growth, as well as nutritional deficiencies and imbalances, overfeeding energy, insulin resistance in the dam and the foal, trauma, and lack of adequate exercise. Strategies directed towards reducing the incidence include reducing the NSC content of diets for foals and pregnant mares, controlling growth rates and avoiding growth spurts in young foals by limiting energy (starch and NSC) intake. Copper deficiency has been implicated.