Developmental Orthopedic Disease

Developmental Orthopedic Disease, or DOD, refers to a number of different ailments which afflict growing horses. The conditions include:

Don't worry if you don't know what a single one of those diseases are...chances are you actually do know of them -- but you probably know their common names instead. So, let's quickly discuss them:

Angular Limb Deformities

ALD is more often known as crooked-legged foals. Foals born with this disease have legs that deviate outward or inward from straight down. Usually the knee joint is the area where the leg is affected, though it can be in the fetlock or hock joint as well.

The cause of ALD is very complex, but is associated with unequal growth of long bones...one side of the bone grows faster than the other, resulting in the limb being deviated from normal. This abnormal growth occurs next to the joint in the growth plate.

Causes of ALD include lameness (which causes abnormal weight-bearing), physitis, excessive body growth in relation to bone/joint growth, and growth plate injury.

Treatment of ALD depends on how old the foal is, how severe the ALD is, and how soon the ALD is diagnosed. In general, the earlier it is diagnosed, the easier it is to treat. Strict stall rest and diet modification, as well as correct hoof trimming, is a part of the treatment for all cases of ALD. Depending on the severity and limbs affected, other means of treatment may include casts, splints, or surgery.

angular limb deformity, one form of developmental orthopedic disease

Physitis

Physitis is nothing more than swelling around the growth plate of a bone. It usually occurs in the bones of the legs, and usually in bones that are closer to the ground.

There are a few theories about why physitis occurs, including malnutrition, faulty hoof growth, and compression of the growth plate. Compression of the growth plate seems to be the most likely cause, as physitis is most often seen in foals that are large for their age, grow quickly, and are top-heavy. It is most often seen in the summer when the ground is hard and dry. It is also seen a lot when the calcium:phosphorus ratio is unbalanced.

Treatment includes reducing feed intake to reduce weight and/or growth rate. The diet also needs to be evaluated to ensure that the calcium:phosphorus ratio is correct (for treatment purposes it should be around 1.6:1) and the amount of protein is not excessive. Confining exercise to small areas where the footing is soft is also part of treatment, as is ensuring that the feet are trimmed correctly and often.

Subchondral Bone Cysts

Subchondral bone cysts are small holes in the bone. They usually occur when the cartilage has excessive pressure or stress placed on it (such as happens during quick growth).

These cysts most often occur in the stifle. Some horses respond to a conservative treatment of 4-6 months of rest and treatment with bute. If the horse doesn't respond to this treatment, the only other option is surgery. However, since surgery has very favorable results, sometimes it is done before the conservative treatment is attempted.

Osteochondrosis

Osteochondrosis (OC) occurs when cartilage fails to harden into bone. The more severe form of this disease is osteochondrosis dissicans, or OCD. When the cartilage fails to harden into bone, a flap of cartilage remains on the articular cartilage or growth plate. OC is a fairly wide-spread disease, affecting up to 30% of some breeds.

There is a "window of susceptibility" for each joint, during which the cartilage is forming into bone and can be affected. Once this window has passed, it is almost impossible for the problem to be corrected without surgery. However, before this window passes, it is possible for many mild cases of OC to resolve themselves over time. Because of this, it is essential that growing foals have a balanced diet, so that a diet problem doesn't prevent the lesions from resolving themselves.

Flexural Limb Deformities

Flexural Limb Deformities (FLD) are often more well-known as "contracted tendons." In FLD, the heel is pulled up off the ground causing the foal to stand more on the toe instead of a flat surface of the hoof.

FLD can occur because of bad positioning in the uterus, limited exercise, overfeeding, and dietary imbalances.

Excess Energy

So, what do all of these diseases have in common? They all appear to be linked to (and possibly caused by) excess energy intake in growing horses.

Young horses that are fed to achieve quick and excessive growth appear to be the most susceptible. It does not appear to make a large difference what the diet is composed of...if they are fed in excess of energy requirements, foals appear to be at a larger risk for developmental orthopedic disease.

It is thought that high levels of starches and sugars may contribute to hormonal imbalances in foals. These hormonal imbalances then affect the insulin response, and higher levels of insulin are often found in the blood of foals suffering from OCD. It is known that high starch/sugar diets affect the insulin response, but at this time it is unknown (due to much conflicting data) whether or not this promotes occurrences of developmental orthopedic disease.

So, until more research is done, it is best to conclude that diets excess in energy might promote developmental orthopedic disease. As a result, growing horses will benefit from being fed a diet that promotes moderate growth rates instead of fast growth rates.

Mineral Imbalances

Unlike the studies about excess energy's relation to OCD, there is clear evidence that unbalanced mineral intakes cause OCD.

OCD can be caused by feeding a diet with an unbalanced calcium:phosphorus ratio, even if the foals have normal weight gain.

Copper is another important mineral related to OC and physitis. Because copper is an important part of collagen (which is an important part of the bone matrix), inadequate intakes can cause both OC and physitis.

Exercise

exercise can prevent developmental orthopedic disease



Exercise is a very important part of a foal's life. Exercise causes greater bone turnover and remodeling, which is a good thing, and helps make the young horse's bones stronger. Both voluntary and enforced exercise both prevent developmental orthopedic disease compared to foals that are kept in confinement with little or no exercise.

However, on the flip side, intensive exercise can cause developmental orthopedic disease.

Therefore, it is ideal to provide the growing foal with as much voluntary exercise as possible, and only supplement with enforced exercise if voluntary exercise is not possible.


Though the causes of developmental orthopedic disease are complex, and probably all related, it appears that the best way to prevent this set of diseases is to ensure that pregnant mares and growing foals are fed a balanced diet, and that they are not fed in excess of energy requirements. In addition, foals should have as much voluntary exercise as possible.


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