Rocky Bay Equine Newsletter, July 2019

This foal was born with crooked front legs, we were able to modify his bone growth to balance and improve his conformation.

Growing a Horse is a Process of Adaptation

Growing a skeleton is hard work and it doesn’t happen overnight. While horses are capable of outrunning a human within a few hours of birth they are not skeletally mature until they reach 6 years of age. (Give or take 6 months or so.) A process called endochondral ossification is responsible for converting the cartilage precursors of long bones in the fetus into the solid bony scaffolding of the adult horse. The most rapid growth occurs in the first months of the foal’s life. By 60 days the average riding horse will reach 75% of its ultimate height at the withers and by 18 months it will reach 90% of its mature height. Based on compiled data, mostly from Thoroughbreds, it was determined that most lower limb growth is complete by their first year of age. They also found that conformation changes can be significant as the foal matures. This adaptability is key to applying management techniques to optimize an individual’s development.

It is not uncommon for a foal to be born with some inconsistencies in alignment that we call "angular limb deformities". One of the most common of these is carpus valgus or "knock knees". Over time, several methods have been developed to address this problem and in the process we've learned how remarkably malleable and adaptable a newborn foal skeleton is. While severe cases of mal-alignment may still require surgical intervention, we have found that in many circumstances we can change the rate of growth across the epiphysis by applying an irritant to the side that we want to grow faster. The key to these discoveries has been understanding how bones grow and mature.

Endochondral ossification begins before birth. By the time the foal hits the ground each long bone in the skeleton is growing in length from specific areas called growth plates or epiphyses, one at each end of the bone. In foals, you can easily see the growth plate of the distal radius as a protuberance just above the knee (carpus). This growth plate is what they are referring to when they say it’s best not put youngsters into heavy work until the “knees are closed”. From birth to around 2 years the marrow cavities develop in the center shafts of long bones and the growth plates at each end gradually convert cartilage into bone as they lengthen and mature. The plates (epiphyses) are considered closed when all the cartilage has become bone with only the epiphyseal “scar” remaining as evidence of once active growth.
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.

PLAN AHEAD to keep your animals safe and sane over the 4th of July

Give us a call now if you anticipate needing some help keeping your animals happy during the upcoming fireworks. Every year we hear or see horror stories of the adverse effects of our celebration on terrified animals large and small.
Rocky Bay Equine Veterinary Services  
  (253) 858-4529   (360) 876-1544
Vaughn / Gig Harbor, WA 98394    find us on FACEBOOK