Osteochondrosis (OCD)

One of the more serious aspects of the DOD complex is OCD.
Unlike physitis, OCD may result in a debilitating lameness in many instances reducing or eliminating any chance of an athletic career.
Many horses have had their working life shortened with arthritis or chips that is related to OCD damage in joints as a young horse.

OCD is a disorder involving the maturation of cartilage in the growth of the bone. There is a failure of the calcification of cartilage that occurs during normal growth of long bones. This leaves a plug of retained cartilage in normal subchondral bone and results in the separation of cartilage from the underlying bone resulting in the formation of subchondral cysts, chips and cartilaginous flaps. Some OCD may not be clinically obvious until later in life when wear and tear results in signs of arthritis. In other cases a weanling or yearling will have a swollen joint and they may be lame. (pic right - hock joint of a yearling)

The diagnosis is made by taking X-rays and it is most frequently seen in the fetlock, hock and stifle joints. Surgery can be used with varying degrees of success, but some horses respond to confinement and medical treatments. A number of causes of OCD have been proposed, yet the specific cause is far from understood. It is difficult to determine if indeed the incidence of the problem has increased or if the condition is being diagnosed more frequently due to superior radiographic techniques and equipment. With respect to the trace mineral theory, careful balancing of rations containing liberal concentrations of copper and zinc have resulted in only a slight reduction in the occurrence of OCD, emphasizing the multifactorial cause of the problem. However remember to supplement the pregnant mare as well as the foal.

Other factors currently under consideration include low calcium and high phosphorus intake, high calcium intake in mares and abnormal hormonal responses to normal or excessive carbohydrate intake. Some young horses may be insensitive to insulin and have an excessive insulin response to grain. This is thought to have an indirect negative impact on cartilage maturation into bone. Contrary to popular belief, high protein does not cause OCD or other DOD conditions
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Exercise is an important preventative factor and Dutch research has shown that forced exercise reduced the incidence of OCD dramatically when horses were fed a risky diet. You should avoid confining foals, weanlings and yearlings as confinement weakens bones and damage may occur when they go back in the paddock.

If they need to be confined for more than a few days provide a graded return to unrestricted exercise, or exercise the horse by walking or lunging. We do not need to box young horses to avoid poor weather and they should be in the paddock as much as possible. Make sure paddocks are large enough to allow babies enough room to run around, however don't allow youngsters to exercise to the point of exhaustion.

Rapid growth creates an increased risk of OCD and this has recently been documented in research by Kentucky Equine Research. In this study weanlings with hock and stifle OCD were larger than unaffected foals of the same age, whilst some cases of OCD in fetlocks were small foals that grew rapidly to catch up. It is best to try and avoid growth spurts and rapidly growing or fat foals should be weaned early.

It is likely that genetic, nutritional, environmental and endocrine components contribute to the etiology and to obtain a decrease in incidence all must be considered.

Until the cause of OCD is better understood it is appropriate to take a conservative approach to the nutritional management of affected populations of horses. Rations should be designed that meet, but do not significantly exceed, the horse's requirements for all nutrients, with specific emphasis on copper, zinc, manganese, calcium and phosphorus.

Once formulated the ration should be fed in a manner that results in moderate rather than maximum growth rates and maximizes the forage rather than the grain part of the diet. Young horses should not be allowed to get fat and ideally you should be able to see some ribs and certainly feel them easily.

It is recommend you feed no more than 1% of body weight as grain or concentrates to young horses which equates to approximately 1/2 kg per month of age until 6 months of age then level off the grain increase. Many Warmbloods do not need this much grain and a reduction in intake of a prepared feed may create a diet that meets energy and protein needs for growth but is deficient in minerals. In this instance you need to add extra minerals from a supplement or balancer pellet. Many feed companies and veterinarians offer diet formulation advice to breeders.

Article by - Dr Peter Huntington
Kentucky Equine Research, Inc