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. 
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.
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). 
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. 
It is most frequently diagnosed in young animals.  Research shows that horses with this condition do not form cartilage normally.
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. 
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.
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.
OCD is now believed to be multi-factorial; several factors usually act together to cause the pathology. These factors include: 
- 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)
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. 
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. 
In 1988, a study showed that foals raised on diets that are severely deficient in copper develop joint abnormalities and stilted gaits. 
Copper is important for enzymes that build cartilage, but the precise amount required to prevent OCD is under debate.
However, it is important to ensure that your growing horse’s diet provides adequate copper and zinc, not only to support joint health but for many other processes in the body as well.
Lack of movement as well as trauma from excessive exercise have been linked to cartilage abnormalities.
In growing animals, consistent low-impact exercise improves cartilage thickness and composition.  Horses that are confined to box stalls have significantly less production of proteoglycan (a protein in soft tissues) than those that are exercised. 
However, excess exercise could cause trauma to the joint and result in cartilage damage. In particular, lesions that progress to fragments could be due to trauma and are most commonly seen in Standardbreds. 
In the first 5 months of age, free access to pasture is best. This will provide the foal with plenty of opportunity for low-impact exercise and supports optimal bone development. 
Some breeds of horses are more likely to develop OCD than others, suggesting there could be a genetic link. The prevalence of OCD ranges from 1.4% to 64% across all breeds studied to date.
The heritability of the condition – a measure of how well genetics explains different traits – is estimated at 0.02 to 0.46. This means that anywhere from 2% to 46% of the condition can be explained by genetics. 
There is no single gene that has been linked to OCD and there is currently no simple genetic tests available to determine your horse’s risk of this condition.
Instead, it is likely that multiple genes contribute to the horse’s risk of OCD. 
Symptoms of OCD
Not every horse with OCD will develop visible symptoms, but the condition does cause clinical signs in 5 to 25% of affected horses.
Most experience mild to moderate symptoms, such as swelling in the joint.  This increases pressure in the joint which can lead to pain.
The next most common symptom is lameness, which varies with the location and severity of OCD.
Many horses are sound at a walk but may show lameness at a faster gait. Lameness is often more prevalent once horses with OCD begin training or racing. 
Most OCD lesions develop before a horse is 7 months old, but the condition may not be diagnosed until later in life once training begins and the joint becomes stressed. 
OCD lesions are commonly diagnosed during pre-purchase exams. This is because many horses don’t show clinical signs but the lesions are noticed on x-rays during the exam.
In addition to looking at the horse’s symptoms, there are four methods used to diagnose OCD:
- Radiography: Using x-ray images to look for lesions in the joint
- Athroscophy: Using a small camera to look inside the joint
- Ultrasound: Using ultrasound imaging to look for lesions in the cartilage
- Biomarkers: A blood test for indicators of poor joint health
Radiography is the most common method for diagnosing OCD. X-rays can identify lesions as well as loose bony or cartilaginous fragments in the joint. 
OCD is often bilateral – meaning it affects both sides of the body – and each affected joint typically has one or two lesions.
If lesions are found in one joint, radiographs should also be done on the opposite side even if there is little or no swelling in that joint.  In horses with fetlock OCD, lesions can even be quadrilateral – affecting all four joints. 
In some cases, lesions will not show up on x-rays and are only diagnosed through arthroscopic examination. 
In this procedure, a veterinary surgeon makes a small incision near the joint. She then inserts a narrow tube attached to a small video camera to have a better look inside the joint.
Ultrasound, which allows for imaging of the cartilage, is another option that appears to have some advantages over radiography, especially when imaging the stifle.
Using radiography in conjunction with ultrasound can also be beneficial in some instances. 
Another way to diagnose OCD is through the use of laboratory testing. These tests look for biomarkers, including molecules found in synovial fluid or blood, that serve as early indicators of abnormalities related to OCD. 
This method is not used as commonly as radiography and arthroscopic examination.
Three categories of OCD diagnosis are generally recognized: 
- Those showing clinical and radiographic signs
- Those showing clinical signs but without radiographic signs (shows lesions with arthroscopy)
- Those showing radiographic signs but no clinical signs
Your veterinarian will evaluate your horse’s signs and symptoms to determine the most appropriate treatment plan.
Treating and Managing OCD
The appropriate treatment for horses with OCD will depend on the severity of the condition and which joints are affected. The following are the most common treatment options:
If lesions do not create cause for concern, rest and recurring radiography to check for worsening of lesions are usually sufficient. The good news is that many lesions do tend to heal on their own.
Horses that are of training age should be put on a restricted exercise schedule and limited to low-intensity work. Once the lesions have healed, the horse can resume normal activity.
Surgical debridement involves surgically examining the affected joints and removing damaged cartilage and bone chips.  This treatment is only required in more serious cases of OCD.
Horses diagnosed with lesions after 18 months of age – especially with lesions in the fetlock and stifle – are good candidates for surgical intervention. Hock lesions that don’t heal on their own also experience good outcomes surgery. 
In the past, OCD lesions were debrided through a procedure known as arthrotomy in which a large incision is made in order to surgically explore the joint.
Today, most surgical debridement is done arthroscopically which has a lower risk of infection and faster recovery time. 
Nutritional management should never be overlooked when dealing with OCD. Many researchers consider nutrition to be one of the top ways to prevent this condition from ocurring.
Excessive energy intake can lead to rapid growth, predisposing young horses to the condition. 
Growing horses should be fed a balanced forage-based diet to limit the risk of this condition. Feeding excess amounts of easily digestible carbohydrates (such as high-NSC grains) can lead to hormonal imbalances which may interfere with the development of healthy cartilage.
One study showed that foals with OCD lesions were more likely to have normal radiographs 12 months later if they were not fed concentrates during the intervening period. 
Deficiencies in the vitamin and mineral content of the diet also contribute to increased risk and severity of OCD. It is recommended to get a hay analysis and work with a nutritionist to provide balanced levels of minerals in the diet.
Medications are typically the last resort for treating horses with OCD. Sometimes, pharmaceutical drugs are unavoidable, especially if synovitis (inflammation of the joint) develops.
In cases such as this, intra-articular injections of hyaluronic acid are commonly used. 
Although helpful for relieving pain associated with some joint conditions, non-steroidal anti-inflammatories (NSAIDs) do not appear to be very effective in treating pain related to OCD.
Preventing OCD in Horses
OCD cannot be prevented in every circumstance, but there are measures horse owners can take to support joint development in young horses.
Avoid rapid growth by limiting excess calories in your foal’s diet. For many growing horses, high-quality forage will provide the protein they need for healthy growth without supplying excess calories.
If you are feeding a low-quality forage, added calories can be supplied from highly digestible fibre such as molasses-free beet pulp. Our nutritionists can help you identify feeds that will not increase blood sugar and insulin levels.
Another option is to use oil as a source of calories instead of grains. Oils that are high in omega-3 fatty acids – in particular the anti-inflammatory DHA – can be beneficial for reducing inflammation and supporting joint comfort.
Environment is another important and sometimes overlooked factor in the development of OCD. Confining young horses in stalls or small paddocks can encourage OCD development.
Studies show that keeping young horses at pasture and allowing for plenty of movement can both prevent and help to heal OCD lesions.  Turnout also supports bone and joint health, metabolic health and overall well-being.
Prognosis for Horses with OCD
Osteochondritis dissecans is a worrying condition for any horse owner that is caring for a growing foal. But the good news is that the majority of lesions heal spontaneously, especially with diet and management changes.
Spontaneous healing tends to yield better results than surgical debridement. Allowing horses time to recover and implementing good management techniques is always preferred as the first method of treatment. 
Horses that are treated surgically still generally have a good prognosis for athletic performance. However, horses with OCD lesions in some locations, such as the shoulder, may have a poorer prognosis.
If lesions do not heal spontaneously and are not surgically removed, the prognosis for future soundness is lower. 
OCD is a common and often temporary disease affecting the joints of young horses. Severity varies from horse to horse and depends on which joint is affected.
Fortunately, there are many things you can do as a horse owner to both prevent and treat the condition.
Consult with your veterinarian if you suspect your young horse may be developing OCD or other joint problems.
You can also submit your horse’s diet for a free evaluation by our equine nutritionists. Our nutritionists can help you design a feeding plan to support healthy growth that will lower the risk of OCD.
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