Physitis in Young Horses: Swollen Growth Plates and What to Do
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By Dr Duncan Houston
Enlargement around a foal’s knees or fetlocks is often blamed on growing too quickly. Growth-related problems do occur, but swelling and lameness still need a diagnosis.
Physitis, sometimes called epiphysitis, affects the growth plates of immature bones. Early assessment helps separate manageable developmental disease from infection, injury or a developing limb deformity.
Quick Answer
Physitis can cause heat, swelling and pain around growth plates in young horses. Management usually involves reviewing growth rate, the complete diet, footing, activity and hoof balance with your vet. A severely lame, feverish or dull foal needs urgent care because infection or trauma can look similar.
What is a growth plate?
A growth plate is the region of cartilage through which an immature long bone lengthens. When that area becomes abnormal or overloaded, the region may appear flared or boxy. The swelling can sit near a joint without being swelling within the joint itself.
The Merck Veterinary Manual’s physitis reference describes heat, pain and swelling and identifies factors including excessive loading, conformation and nutritional imbalance. Radiographs help interpret what is happening beneath the visible enlargement.
Growth plates close at different ages in different bones. There is no single birthday after which every growth-related problem automatically resolves.
Is the feed to blame?
Excess energy intake and rapid weight gain can contribute to developmental orthopaedic problems, but that does not mean a growing foal should be deprived of essential protein and minerals. The whole ration matters, including pasture, hay, mare’s milk where relevant, concentrates and supplements.
The MSD nutritional disease review specifically notes that excess dietary protein does not itself cause developmental orthopaedic disease. Avoid reducing protein indiscriminately or adding calcium, phosphorus or vitamin D without calculating the existing supply.
How urgent is the problem?
| Finding | Action |
|---|---|
| New, fairly symmetrical enlargement with little obvious discomfort | Arrange veterinary assessment and review diet and activity promptly. |
| Lameness, heat, pain or increasing limb deviation | Contact your vet the same day. |
| Marked lameness, inability to bear weight, fever or reduced nursing | Request urgent examination. |
What else needs ruling out?
Septic growth-plate disease, infected joints, fractures, osteochondrosis and soft-tissue injuries are important alternatives. Infection is particularly concerning in young foals and may be present without dramatic fever.
Your vet examines limb alignment, joints, growth plates and the foal’s general health. Radiographs, ultrasound, blood tests or joint sampling may be appropriate. Routine blood mineral values alone cannot establish that a ration is correctly balanced.
When is this an emergency?
A foal that cannot comfortably bear weight, is depressed, stops nursing or develops a hot painful joint needs urgent veterinary care. Do not assume it is merely growing pains. Delayed treatment of infection can threaten future soundness and the foal’s life.
What should you do next?
- Contact your vet and describe the foal’s age, onset, affected limbs and general behaviour.
- Limit strenuous or uncontrolled activity while awaiting instructions. Keep mare and foal safely together when appropriate.
- List every feed and supplement with weighed amounts and product labels.
- Arrange a balanced ration review with your vet or equine nutritionist.
- Follow the prescribed activity and farriery plan, recording swelling, comfort and limb alignment.
Restricted activity may be needed during painful inflammation, but the safe area and duration depend on examination findings. Do not force exercise to straighten a painful limb. Pain medication is prescribed individually; foals are not simply small adult horses for dosing purposes.
Rechecks matter because a comfortable-looking foal can still develop uneven growth or limb deviation. Ask which change should trigger an earlier appointment and when imaging needs repeating.
Common mistakes
- Calling every swollen joint in a foal epiphysitis.
- Starving growth rather than correcting the ration.
- Adding several mineral products without calculating the total.
- Using adult-horse medication left over from another case.
- Waiting for a crooked limb to correct itself without assessment.
Reducing future risk
Aim for steady growth and appropriate body condition. Keep feeding consistent, review rations as the youngster grows and organise regular hoof assessment. Provide safe footing and age-appropriate movement. Genetics, conformation and disease also matter, so excellent management cannot prevent every case.
Frequently asked questions
Is physitis the same as epiphysitis?
Epiphysitis is a commonly used older name; physitis more precisely identifies the growth plate.
Will my foal grow out of it?
Some cases improve with appropriate management, but persistent pain or deformity needs follow-up.
Should I stop all protein?
No. Growing horses need adequate protein. Have the entire ration assessed.
Does every foal need strict box rest?
No universal plan fits every case. The diagnosis, pain and stability determine restrictions.
Prompt assessment and a balanced growth plan are more useful than simply cutting feed or adding supplements.
For help understanding your horse’s care and preparing questions for your veterinarian, visit ASK A VET™. Urgent signs need an equine veterinarian in person.
