MEDICAL ARCHIVES

08.02.2006

Joint Disease in Horses

Managing Joint 'Wear and Tear' and Arthritis by John Kohnke BVSc RDA

The lower limb joints of racing, equestrian and working horses are subjected to heavy loading during exercise, which is increased at speed and especially when cornering or turning at the canter or gallop. Loading of up to twice the animal's body weight is borne by the limb joints at the gallop in a straight line, and up to 5000kg (or about 500psi of joint surface area) downward force is placed on a front limb as it bears weight when cornering at the gallop in a race.

Joints are subjected to overload and 'wear and tear' type injuries to the weight bearing surface of the cartilage layer covering the ends of the bones within the joint cavity. As a horse progresses in training, the joint cartilage thickens in response to the increased load bearing.

The joints most affected by excessive loading include the fetlock joint in 2-3 year old horses as it flexes down and hits the track or ground surface during the gallop and the knee joints in 3-4 year old galloping or working horses that are subjected to high loading and concussion as the front limb bears weight at each stride. About 80% of lamenesses occur in the front limbs of galloping horses, and 80% of these occur in the bones, joints and tendons below the knees.

When horses work at speed, their knees, hocks and fetlocks in particular, as well as other joints, are subjected to high concussion, load compression, twisting and sprain injuries.

The Joint Environment

The joint cartilage surface is lubricated by high viscosity joint fluid to reduce friction on the cartilage surfaces as the joint maintains its resilience and resistance to wear, as well as replenishing and repairing itself after each gallop or hard workout.

The joint cartilage that covers the ends of opposing bones of a joint within the joint cavity, consists of spongy layers of tissue formed by chrondocytes . The cartilage contains structural compounds called glycoaminoglycans (GAG's), other bonding substances and water.

Joint cartilage has no blood or nerve supply and the cells depend on the joint fluid for nutrition. When load is placed on a joint, the cartilage is depressed and "squashed", forcing water out into the joint fluid to provide a shock absorbing function to protect against concussion. When the limb leaves the ground, the compressed joint cartilage rebounds, drawing water and nutrients back from the joint fluid to reinstate its resilience and hydraulic properties, as well as providing nourishment to the living cartilage cells.

Deterioration of the cartilage layer due to overloading and excessive concussion, reduced nutrient content and lubrication function of the joint fluid in joints under high loading stress, results in destruction of the thin cartilage layer. In severe cases, bone to bone contact within the joint occurs, with inflammation and joint swelling, causing symptoms of pain and lameness. This is often referred to as arthritis or joint swelling. In severe cases, bony reaction develops within the joint, leading to degenerative joint disease and long term lameness.

Traditional Joint Therapy

Over the past 2 decades, anti-inflammatory drugs, such as phenylbutazone ('Bute') and corticosteroids (synthetic cortisone compounds) have been used to reduce pain and discomfort from joint "wear and tear". However, studies indicate that continued use of 'Bute' to relieve joint swelling and lameness can actually increase the rate of deterioration of joint cartilage. Corticosteriods injected into the joints to mask pain and reduce inflammation also result in calcification and physical deterioration of the cartilage layers. However, in some cases, use of these compounds, combined with rest, is helpful in reinstating the joint environment ravaged by inflammation.

A New Development - Joint Food

Rest from training for a period relative to the severity of cartilage damage will usually enable the cartilage to repair itself in minor 'wear and tear' conditions. However, this process is slow and may be delayed by an inadequate supply of raw materials for cartilage repair in the diet. Rest or downtime from training is also expensive and can delay opportunity for a horse to compete for long periods.

Over the past 5 years, the use of nutritional compounds, including glucosamine, chondroitin sulfate, shark cartilage, Vitamin C, and the trace-minerals copper, zinc, manganese and selenium in a supplement form have been introduced as a new form of treatment. They provide sources of the structural components of joint cartilage required to maintain joint flexibility, resilience and function.

Glucosamine, an amino acid-sugar complex, is one of the major nutritional ingredients of the bonding and structural glycoaminoglycan compounds in joint cartilage, in combination with chrondroitin, another structural component of cartilage cells. It also provides a natural anti-inflammatory action, and in human studies, glucosamine is credited with a pain relief effect in arthritis sufferers.

Vitamin C is essential for the formation of collagen, which is also a structural component of joint tissue. Vitamin C is the major antioxidant found in joint fluid that protects the cartilage against destructive anti-inflammatory compounds. The trace-mineral copper is required for the development and maturation of the cartilage cells to withstand loading.

Studies of joint abnormalities in growing horses have linked low copper, zinc and manganese in the diet to poor joint and cartilage formation. These trace-minerals are also the minerals that are used in natural anti-inflammatory compounds that protect tissues and cartilage against "free-radical" damage that occurs during inflammatory reactions in overloaded and deteriorating joint structures.

Repair and Maintenance of Cartilage Health

Nutritional supplements that contain these ingredients, such as Nutricart® for horses, provide the raw materials necessary for repair and rebuilding of joint cartilage, and are widely recognised as being beneficial in maintaining joint flexibility and function in racing and working horses.

After diagnosis of joint cartilage 'wear and tear', or when recovering from joint injury or following joint surgery to remove diseased or damaged cartilage and bone reaction, supplements containing glucosamine, shark cartilage as a source of chrondroitin, and the other structural and protective nutrients have been shown to be helpful in repairing and restoring the joint environment.

Usually a higher supplement rate is initially given twice daily for 2-3 weeks to assist the replenishment and repair processes. The dose rate is then reduced to a daily maintenance level to maintain healthy and resilient joint cartilage. Horses can remain in training and have the opportunity to continue to race or compete in the majority of cases.