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The term “osteoarthritis” (OA) incorporates three interconnected themes: bones, joints, and inflammation. Degradation of cartilage, growth of bone spurs, and development of fluid-filled cysts lead to problems like joint pain, stiffness, and decreased range of motion. These developments explain another descriptive term: degenerative joint disease (DJD).

Horses with OA usually develop lameness that limits their ability to perform. As pain keeps them from moving freely, they progress into muscle weakness and a redistribution of weight onto the less painful limbs.

Aquatic exercise programs have become popular for arthritis patients, both humans and other species. Being partially supported by water reduces the weight and mechanical stress borne by limbs and joints; the slight resistance provided by moving through water increases muscle strength without significant strain; and immersion in water causes slight pressure on the limb tissues, reducing edema and increasing circulation.

Studies have been conducted using horses in various types of aquatic exercise programs and measuring a number of body functions. Horses exercised in an equine swimming pool have shown improved cardiovascular function and more development of fast-twitch muscle fibers, both of which support increased aerobic capacity. Another result of swimming exercise, as shown by fine-wire electromyography studies, is greater muscle intensity of the thoracic limbs during swimming as compared to walking on the ground. A further study showed that horses tended to use fewer and longer strides when water was mid-forearm deep as compared to more and shorter strides in pastern-deep water.

Horses suffering from induced OA in one knee were used in a Colorado State University study to measure the effect of water-supported treadmill exercise on diminishing the progression of the disease. Weight-bearing forces, muscle activation patterns, knee joint range of motion, clinical lameness signs, alteration of balance control, and cellular changes within the joint were all measured.

Results showed that horses exercised on the aquatic treadmill had symmetric loading of the forelegs, while control horses (OA induced in one knee, but exercised on dry land) showed less weight being borne on the OA leg. Activation of selected forelimb muscles was also symmetric in the aquatic-exercised horses but not in the control horses. Range of motion for the aquatic-exercised horses was significantly improved a week after beginning the water exercise program, and this improvement continued throughout the study. By the end of the study period, range of knee motion returned to the pre-OA level for the water-exercised horses but not for the control horses. Amount of scarring within the knee and inflammation within the synovial lining also showed lower levels in aquatic-exercised horses compared to controls, and water-exercised horses showed improved balance control in various stance positions. The researchers concluded that aquatic treadmill exercise is a viable therapeutic option for horse with OA.

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