Developmental orthopedic diseases (DODs) refer to a range of non-infectious conditions that affect the musculoskeletal system of growing horses.
These conditions arise from an interruption in the normal development of cartilage, bone, or soft tissue (joint capsule, tendon, or ligament).
While some developmental issues are apparent at birth, others occur later as the horse grows. Conditions such as osteochondrosis and physitis can affect any breed of horses and are a common cause of pain and lameness. 
Some developmental orthopedic diseases influence future performance, depending on what part of the horse’s joint is affected. 
Developmental Orthopedic Diseases
The exact percentage of horses affected by DODs is unknown, however, prevalence is known to be high in certain breeds.
In a study of 392 Warmbloods, Standardbreds, and Thoroughbreds, 66.3% of foals were affected by developmental orthopedic diseases. 
Key factors in the development of equine orthopedic disorders likely involve a combination of the following causes: 
- Genetics: Some breeds may be genetically predisposed to DODs
- Nutrition: Lack of complete or imbalanced nutrients provided in the diet of pregnant or lactating mares and foals
- Rapid growth rate in foals and obesity due to excess dietary energy provided in their feeding program
- Trauma or stress exerted on developing cartilage and bones
- Excessive exercise at a young age or a lack of activity
A thorough physical evaluation by a veterinarian is necessary to identify abnormalities of the developing skeletal system in young horses. 
If your veterinarian suspects your horse has a developmental orthopedic disease, diagnostic radiographic or nuclear imaging and blood tests may be required to make an accurate diagnosis.
6 Common Developmental Orthopedic Diseases in Horses
1) Equine Osteochondrosis
Osteochondrosis describes abnormalities in the differentiation and maturation of cartilage. The condition impairs the normal bone formation process in which cartilage is gradually replaced by bone (endochondral ossification). 
Physical signs of osteochondrosis vary according to the joint(s) affected. Common signs include non-painful joint swelling and stiffness and an upright limb conformation.
Foals under six months of age with osteochondrosis may spend more time lying down and have difficulty moving normally. Increased joint stiffness and lameness may become apparent with the start of training.
Physical examination, x-rays, ultrasonography, arthroscopy, scintigraphy, or magnetic resonance imaging (MRI) are often used to diagnose osteochondrosis.
Diagnostic imaging often indicates abnormal cartilage growth and the presence of bone fragments in the joints when osteochondrosis is present.
Treatment of osteochondrosis depends on the severity of the condition and the specific joints affected. Horses with mild cases of osteochondrosis may recover without intervention.
If rapid growth is occurring in horses with osteochondrosis, restricted exercise and dietary modifications that reduce energy intake can help address the condition. Appropriate mineral supplementation is also required to address deficiencies in the diet. 
In some cases, surgery may be necessary to restore joint health. Surgical intervention may be necessary to remove damaged cartilage, osteochondral fragments, and compromised bone present beneath the affected cartilage. 
2) Equine Physitis (Physeal Dysplasia)
Previously referred to as epiphysitis, physitis is a DOD that describes swelling around the cartilaginous growth plates (areas within the bones from which growth or lengthening occurs) of specific long bones. One or multiple growth plates may be affected. 
Physitis is most prevalent in young horses that are growing rapidly and carrying excess weight. If a foal grows faster than its growth plates can develop bone (ossify), the bones can sustain structural damage. 
Potential causes of physitis include poor or imbalanced nutrition, such as imbalanced calcium to phosphorus ratio or mineral deficiencies in the diet.
Overfeeding and rapid growth are not believed to be the only factors that contribute to physitis. Instead, several factors are likely involved in the development of the condition.
Affected joints typically feel warm and firm when touched and have a boxed-shaped appearance.
Radiographs, ultrasound, and MRI help confirm a diagnosis of physitis. The most common sign of the condition is irregular and widened growth plate. To diagnose infection as a cause of physitis, synovial fluid is extracted from the affected joint and assessed. 
In some cases of physitis, the condition resolves on its own as the skeleton matures and growth plates close. However, some horses require treatment to address the condition.
Treatment strategies for physitis related to rapid growth aim to slow this rate and possibly reduce body weight by lowering energy intake.