CHAPTER 18 Nutritional Factors in Developmental Orthopedic Disease
Developmental orthopedic disease (DOD) is a term used to encompass many orthopedic problems in the growing horse. It includes physitis, osteochondrosis, subchondral bone cysts, cervical vertebral malformation, flexural limb deformities, and angular limb deformities. Clinical signs include lameness, joint effusion, change in posture or limb positioning, and crooked limbs, depending on the disorder. Many of these disorders affect bone and joint formation and sometimes result in abnormal or defective cartilage development, particularly at the metaphyseal or epiphyseal growth plates. Even when this is not the case, such as in horses with acquired flexural deformities, the pain associated with other DODs, such as physitis, may result in less weight-bearing in the limb and shortening of the suspensory ligament or flexor tendons as ground force decreases in response to pain. Although many DODs have no relationship to each other and share no commonality other than affecting growing horses, in instances such as this, a relationship seems to exist. Additionally, it is not uncommon for a horse to have several DODs at the same time.
POTENTIAL NUTRITIONAL CAUSES OF DEVELOPMENTAL ORTHOPEDIC DISEASE
Copper
Insufficient copper in the diet of broodmares has also been implicated as a cause of DOD. The series of papers from New Zealand mentioned previously suggested that supplementation of mares grazing low-copper pasture (containing 4.4 to 8.6 ppm copper) had a greater effect on reducing the severity of physitis scores in their foals at 150 days of age and the prevalence of articular cartilage lesions than did supplementation of the foals themselves, suggesting an in utero role for copper in skeletal development. However, supplementation of copper in mares did not eliminate DOD in their foals. In another study conducted in Germany, no relationship was found between copper intake by pregnant mares and development of osteochondrosis in 629 foals from 83 farms.