It is widely believed that exercise and limb-loading in foals help joint cartilage functionally adapt to the rigors of athletic activity. In 2005, Dutch researchers set out to find out if they could verify the concept of functional adaptation of cartilage by measuring the biomechanical (the mechanics of biological activity) properties of cartilage in stillborn horses, and comparing those values to those observed in horses at 5 months of age, 18 months of age, and maturity. Their work was published in the March issue of the Equine Veterinary Journal.

Two sites on the top of the fetlock joint in the forelimb were chosen for testing because they are dramatically different in their biochemical makeup and how they are loaded in the living horse. One site is impact-loaded intermittently, while the other is constantly loaded, but at a lower level.

By looking at the results of the biomechanical tests, researchers confirmed that a newborn foal's cartilage is a "blank slate," or biomechanically homogeneous (exhibiting the same properties over the entire joint surface). Harold Brommer, DVM, of Utrecht University in the Netherlands, explained, "At visual inspection, articular (joint surface) cartilage of the foal looks like normal cartilage of adult horses. However, the results of our study showed that the layer is much thicker and the biochemical make-up is quite different compared to the adult horse. This implies that the cartilage in the foal at birth has not the functional characteristics of the adult horse."

"During early life, the functional characteristics have to be developed under the influence of loading, i.e. exercise, in order to get the functional quality that is needed to sustain loading without suffering injuries throughout life," he added.

Brommer says that there is a tremendous change in the functional properties of articular cartilage before the foal is 18 months old, but that only very minor adaptations are possible after that age (as gathered from examining the mature horses' joints). "Therefore, the first period after birth is of most crucial importance with regard to prevention of joint disease in the horse at older ages," he says.

According to Brommer's team, the development of the functional parameters of articular cartilage during early life is related with a concurrent development in the orientation of collagen fibrils (tiny fibers) in the cartilage. Brommer explains, "In the adult horse, the fibrils have an arcade configuration: parallel to the joint surface in the superficial zone (closer to the cartilage surface) and perpendicular to the surface in the deep zones, which attach to the underlying subchondral bone. So during the period of functional adaptation, the specific orientation of the fibril changes from one configuration to the other. The significance is undoubtedly related to the functional consequences of each fibril configuration."

Understanding cartilage adaptation better should help researchers recommend management techniques and turnout times to horse owners who are raising foals. Brommer says currently, "What we know is that box-rest is not good for the adaptation of the cartilage, but that exercise is very important. The main question is, 'How much exercise?' "

The Utrecht team, in collaboration with other research institutes and laboratories, has been evaluating cartilage specimens from young horses that have had different exercise regimens during their first 18 months of life. Some of the horses were kept on pasture while others had additional exercise superimposed on being pasture-kept. The researchers will report on this topic as soon as the results of this study are available.

Brommer adds, "The main risk of giving a young horse additional exercise is that the exercise may be too much, leading to overloading of the cartilage, which may result in damage on a young age, including joint disease and impaired performance. It is obvious that a thorough investigation in the search for a well balanced exercise program is of utmost importance to achieve the most optimal conditioning of the articular cartilage."

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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