Epiphysitis

Epiphysitis (properly called physitis) is a bone disease of young, rapidly growing horses that is characterized by enlarged growth plates on long bones.  The epiphyseal plates of the bones are literally inflamed as new tissue cannot harden properly in conjunction with the horse’s rapid growth and nutritional imbalance of the feed*.  In severe cases, the end bones of the knees, hocks and fetlocks can actually appear flared, or hourglass shaped.  The youngsters have difficulty moving, getting up and down and appear very stiff and sore.

I became familiar with the disease when I worked with young thoroughbred race horses back in the 1980’s.  At that time, barn managers sought the highest protein rations to feed weanlings and were not as aware of the importance of fat content and mineral balance as they are today.  Many also left babies with their dam longer and allowed free-choice creep feeding without additional supplementation. 

Today, we know that the disease is primarily caused by improper phosphorus to calcium ratio.  Feeds are better balanced and fat content provides appropriate calories to growing youngsters.  However, not weaning foals early still contributes greatly to the number of weanlings afflicted with the disease.  Most babies should be weaned by 4 month in order to better regulate their nutrition.  What occurs when babies are left with the mare beyond that time is that the foal consumes some of his mother’s grain, her supplements, maybe his own grain and supplements as well as pasture or forage, all the while still nursing.  This scenario often results in a diet higher in phosphorus and low in calcium. Weaning early allows regulation of the foal’s nutritional intake and maintaining a proper calcium/phosphorus ratio.

The inflammatory effects of physitis can be reversed in most babies but the more severe the inflammation the longer it takes to correct.  Veterinary intervention is necessary to monitor inflammation and to assist with correcting nutritional imbalances.  The long term affects of the disease can include a predisposition to arthritis in those joints as an adult. 

The disease may be influenced by genetics but following weaning and feed guidelines seems to allow normal development in most foals.

Many Veterinarians recommend mineral supplementation.  All Veterinarians suggest regular exercise in helping to prevent the disease.  Foals do best with lots of room to run and play.  Stall confinement is simply not good the majority of foals.  On the racetrack, supplementation with methylsulfonylmethane (MSM) became popular and I still use it with all the babies we raise, with great success. 

Foaling season is here and it’s never to early to develop a health plan for your weanlings that includes plenty of exercise, balanced nutrition and early weaning.  Physitis can be prevented, so see your Veterinarian for additional information!

*Ossification is the process by which cartilage cells multiply and absorb calcium to thereby develop into bone.