Physitis or epiphysitis is a developmental orthopaedic disease. Physitis is most commonly a disease of heavy, fast growing foals and is often seen in both thoroughbred and sport horse herds. It is more common in foals being supplemented with large amounts of hard feed.
While the term “epiphysitis” is regularly used, the more correct term is physitis. Any medical term ending with “–itis” means that it is inflamed. The physis is the medical term for the growth plate in bones and it is this area that becomes inflamed, hence “phys-itis”.
Physitis is a developmental orthopaedic disease. There are many other diseases included under the umbrella of developmental orthopaedic diseases, such as osteochondritis dessicans (OCD), wobbler syndrome and angular limb deformities. These problems may all occur in the same animal but one does not necessarily lead to the other.
Physitis is most usually a disease of heavy, fast growing foals and is often seen in both thoroughbred and sport horse herds. It is more common in foals being supplemented with large amounts of hard feed. In the authors experience it is also more common in foals that have been raised by cob type foster mares.
The problem is caused by overloading or compression of the spongier growth plate part of the bone. This causes inflammation primarily but can lead to alterations in the growth of the bone, which will cause lasting damage.
In general physitis is quickly recognised by experienced stock people and does not lead to lameness and investigations such as x-rays are not required.
What does it look like?
Physitis appears as a hard, warm swelling over the fetlock or knee, at the level of the growth plate of the long bone of the cannon or the forearm. There is usually a pain response when the growth plate/physis area is pressed upon. Sometimes x-rays may be taken to rule out traumatic causes of swelling such as knocks to the joint. There is no associated swelling of the joint structure itself in cases of physitis.
The most common site for the problem is the fetlock area, usually just above and to the inside of the joint. See photo one above
The knee is also a common site, see photo two below. The hock may also be involved but this is more unusual.
How to avoid physitis
Avoiding physitis is generally a case of providing a balanced diet that provides all the essential nutrients for growth without causing the foal to become overweight. Sounds simple!
So why are there so many people rolling their eyes to heaven while reading this?! In reality physitis can occur with even the most careful dietary management and stockmanship. There would seem to be a genetic predisposition, some horses simply put on more weight quicker than others on exactly the same diet, some may be more sensitive to pressure on the growth plate. Many mares will produce a very rich milk in vast quantities, this is most likely the case with the foster mares. The quality of milk is difficult to manage. It is certainly easier to improve milk quality than to decrease its value. Limiting the nutrition of mares will have some effect but the reproductive status of the mare must also be considered, is she in foal again? the next pregnancy should not compromised.
Subtle dietary deficiencies in essential vitamins and minerals are also likely to have an effect. Calcium, phosphorus, copper and zinc are understood to be the most important factors. Regular analysis of hay and grass as well as the concentrate is advised.
Treatment/management of physitis
The treatment of physitis relies on two key components: box rest and diet restriction. In most cases drugs are not required, but if the foal is lame your vet may recommend anti-inflammatory medications.
Box rest limits exercise, so limits the active compression when the foal is moving about. The amount of box rest required varies from case to case but can be from two weeks to two months. The restriction of diet is so that the foal reduces its bodyweight. Obviously the foal is still growing, and you need to support the growth with vitamins and minerals, do not starve the foal. Calories must be restricted but minerals such as calcium and phosphorus must be provided for continuing normal musculoskeletal growth.
With early recognition of physitis and appropriate intervention the prognosis for foals with physitis is good with most mildly affected foals going on to expected sales and racing outcomes.
Supplementing foals on restricted diet Cal-Gro provides the essential nutrients calcium and phosphorus in the ideal ratio of 2:1, for optimum bone growth in young horses. Cal-Gro also contains MSM, magnesium, copper and zinc, which are necessary for bone growth and cartilage development. Lysine is the limiting amino acid in bone growth and present in mare’s milk, Cal-Gro also contains lysine to maximise bone growth even on low protein diets or restricted pasture access. Silicon which adds strength to bones, joints, ligaments and tendons is also provided by Cal-Gro.