The epiphyseal plates of each long bone mature at fairly predictable rates from the ground up. For example, the pastern bones are mature in 12 to 15 months, the cannon bones around 18 months, the scapula and femur at 3 to 4 years. Parts of the pelvis may take 5 years for the growth plates to fuse. The vertebrae of the neck and back are last to reach structural maturity at nearly 6 years of age. While it’s true that some breeds appear more or less structurally mature at different ages, ie American Quarter Horse vs. Arabian, all horse breeds reach skeletal maturity around the same age of 6 years.
Bone building is a process that includes a great deal of modeling and remodeling. It is an extremely adaptive kind of growth that actively responds to direct stimulation as noted above in treatment of angular limb deformities. Bone growth is also highly responsive to factors such as nutrition and exercise. These responses may be positive or negative in regard to the ultimate structural soundness of the fully mature animal. For instance, developmental orthopedic disease (“OCD” ostochondrosis, defects in bone & cartilage) is linked to diet and is more prevalent in rapidly growing animals. An appropriate dietary balance of protein, carbohydrate (sugar), vitamins and minerals is vital for growing strong, healthy bone. Managing growth rate is important to minimize the risk of DOD. Bone growth is also adapted to load or stress levels in the form of exercise. In the immature animal this is a delicate and time sensitive balance of applying just the right amount of stress to encourage optimal bone development for their job, ie. to withstand the rigors of high speed racing or elite performance, without damaging the developing bone and musculature. Knowing the stages of growth and maturation is important for all owners and trainers to understand and apply to the training of all horses in their care. While it is especially important for animals who will be asked for maximal performances, it’s also important to appreciate that the cervical spine and back are the last areas to become skeletally mature. Asking a young horse to collect beyond his base fitness level, jumping lots of high obstacles, jerking on the head and neck or allowing the animal to pull back when tied are all potentially damaging to the developing horse. Good training is both an art and a science, the best trainers help mold the developing bone, body and brain of young animals into sound, healthy and sane adults. Works for horses and humans alike.