Dealing with early lameness

Pre-purchase examinations of yearlings in Europe and America now include routine X-ray screening for osteochondritis dissecans, known as OCD.
Issue date : 03 July 2009

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Pre-purchase examinations of yearlings in Europe and America now include routine X-ray screening for osteochondritis dissecans, known as OCD. There could be several reasons for this joint disease. For instance, it’s well known that, in fast-growing breeds like Warmbloods and English Thoroughbreds, it is critical to keep the diet balanced after they’re weaned, and restrict the level of easily digested carbohydrates like maize meal to prevent OCD.

Recently, however, it has been suggested that this joint disease is more common in certain bloodlines, and many cases have been shown to trace back to a particular stallion. It may, therefore, be genetic.Although OCD occurs most commonly in young, rapidly growing  weanlings between the ages of eight and 18 months, it’s often only diagnosed for the first time when the horses are put under saddle at two to three years of age or when they start their racing careers.

It is most often found in the hock, stifle, shoulder or fetlocks and is due to abnormal growth of the bone (osteochondrosis) that leads to separation of cartilage inside the joints. These loose fragments of cartilage, sometimes with small pieces of bone attached, move around in the synovial (joint) fluid, causing inflammation and damaging the joint surfaces.

Detecting the signs
The signs usually seen by the owner include swelling of the joints with mild to severe lameness. Most commonly, it is found in only one joint on the same limb, but often the problem is bilateral, or on both legs. For instance both hock joints will be affected, but not a hock and fetlock on the same leg. This is one of the reasons why a genetic origin was suspected.

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X-rays remain the most effective means of diagnosis, although they may be negative in early cases . If the X-rays aren’t clear or if they were negative and the symptoms point to OCD, it’s possible to examine the joint surface with an arthroscope – a special instrument that can be inserted into the joint to photograph and video the joint surfaces.

Costly veterinary treatment
Probably the most difficult form of OCD to diagnose is when it occurs in the shoulder joint. The lameness tends to come and go. Since the usual lameness tests are done on the lower leg, below the elbow, local anaesthetic blocks won’t decrease it.
The shoulder joint is also surrounded by muscle, so no swelling will be seen. In well-muscled yearlings, an X ray of the shoulder can often be done only with sophisticated machines.

If OCD is suspected in the shoulder joint, the veterinarian may also have to take a sample of joint fluid for examination and follow up with arthroscopy. Both these more sophisticated procedures mean that the horse will have to be taken to an equine specialist. Treatment is possible. If there are positive signs of OCD, the veterinarian can remove the loose pieces of cartilage and flush out the joint. Although this is an expensive procedure, it’s usually successful, and the disease doesn’t recur.
This type of veterinary treatment is usually done in sporting horses rather than race horses as it may prevent the horse racing for some time when it needs to be in training.

Diet is known to play a role, particularly giving high levels of concentrate feed, such as maize, to weanlings. Mineral imbalances – specifically calcium, phosphate and zinc, especially if paired with low levels of copper – have also been implicated in OCD.
It’s important that growing horses should be fed a diet specific to their needs and several feed manufacturers stock such feeds.Research has found a definite genetic link in OCD, as there was no other explanation where a group of weanlings under the same conditions and eating the same feed didn’t all get it. In Europe, pedigree studies have pointed to a specific stallion being an ancestor of many OCD-positive weanlings. This means the condition could be largely eliminated by sensible breeding strategies.E-mail Dr Mac c/o [email protected]      |fw