By Hilary M. Clayton, BVMS, PhD, Dipl. ACVSMR, MRCVS

Horses are products of their genetics and the environment we provide for their growth and development. One of the most important choices we make when managing horses during the first few years of their life is whether they are stabled or turned out, and for how long. Different types of exercise are necessary to stimulate adaptation of the different locomotor musculoskeletal tissues (bone, articular cartilage, muscle, ligament, and tendon), and these tissues are most responsive at different ages. Therefore, young horses need a sufficient amount of appropriate types of exercise at the right times in their lives to fulfill their athletic potential and reduce their risk of injury.

Researchers have shown that 24-hour-a-day turnout during the early months of a foal’s life is the gold standard for developing a strong, resilient locomotor system. Management approaches in which foals are kept in stalls even for part of the day are less effective in stimulating optimal locomotor tissue strength. This is especially true for the superficial digital flexor tendon (which runs from the back of the knee [or hock] all the way down to the back of the pastern in each limb and acts as a “sling” to support the fetlock to help it bear the animal’s weight) and the suspensory ligament (which runs down the back of each cannon bone). Both structures are frequently injured in equine athletes. These soft tissues reach their maximal strength by the time the horse is 2 years of age, ­after which they are no longer able to adapt to the stimulus of conditioning.

Another benefit of turn