Physitis in Foals: Causes, Signs and What To Do

By Dr Duncan Houston

Swelling around a young horse’s knees, fetlocks, hocks, or pasterns can be easy to dismiss as “just growing pains.” Sometimes it is a mild developmental issue. Sometimes it is the first sign that the foal is growing too quickly, carrying too much weight, loading the limbs unevenly, or developing a more serious orthopedic problem.

Physitis means inflammation of a growth plate. In foals and young horses, the growth plates are active areas of cartilage where bone lengthening occurs. When those areas become inflamed, they may look swollen, warm, boxy, or painful. The key is working out whether this is a manageable growth-related issue or something more serious, such as infection, fracture, osteochondrosis, or angular limb deformity. Merck Veterinary Manual describes physitis as heat, pain, and swelling around the growth plates of certain long bones in young horses, with causes including nutritional imbalance, conformation, excessive exercise, obesity, and toxicosis. (Merck Veterinary Manual)

Quick Answer

Physitis is inflammation of a growth plate in a foal or young horse. It usually causes firm swelling, warmth, tenderness, and sometimes lameness around areas such as the knee, fetlock, hock, or long pastern region. It is commonly linked with rapid growth, excess body weight, hard ground, excessive exercise, conformational loading, and nutritional imbalance, but infection and other orthopedic diseases must be ruled out if the foal is painful, lame, unwell, or the swelling is severe or one-sided. (Merck Veterinary Manual)

What Is Physitis?

A physis is a growth plate. In young horses, growth plates are the areas where cartilage gradually changes into bone as the skeleton develops.

Physitis happens when this area becomes inflamed or overloaded. The swelling is usually seen near the ends of long bones, especially around:

• The lower radius, just above the knee

• The lower cannon bone, near the fetlock

• The lower tibia, near the hock

• The long pastern region

Merck notes that physitis most commonly affects the distal radius, tibia, third metacarpal or metatarsal bone, and proximal first phalanx. These are exactly the areas owners often describe as “puffy knees,” “big fetlocks,” or “boxy joints.” (Merck Veterinary Manual)

The important point is that physitis is not just a cosmetic swelling. It means the growing skeleton is under stress.

What Does Physitis Look Like?

Physitis can look different depending on severity, age, and which growth plates are involved.

Common signs include:

• Firm swelling around a growth plate

• Warmth over the swollen area

• Tenderness when touched

• A boxy or enlarged appearance near the joint

• Mild to moderate lameness

• Stiffness when moving

• Reluctance to keep up with the mare or other foals

• Spending more time lying down

• Upright limb posture or developing limb deviation in some foals

In mild cases, the foal may still be bright, active, and nursing or eating normally. In more concerning cases, the foal may be clearly lame, painful, dull, feverish, or reluctant to move.

A practical rule: symmetrical, mild swelling in a bright, otherwise normal foal is usually less alarming than sudden, painful, one-sided swelling with lameness or fever. The second situation needs urgent veterinary assessment.

What Age Do Foals Get Physitis?

Physitis is most often seen in growing foals and young horses, especially during periods of rapid growth. It is commonly recognised in fast-growing foals around 4 to 8 months of age, but it can also occur in younger foals and in yearlings, particularly those that are heavy, well-muscled, or starting training. Merck describes physitis as common in fast-growing, heavy-topped foals and notes it can also be seen in young horses around 18 to 24 months that have begun training. (Merck Veterinary Manual)

So, while the classic owner concern is the 3 to 6 month old foal with swollen growth plates, it is better to think of physitis as a growth and loading problem in young horses, not just a narrow age-based condition.

What Causes Physitis?

Physitis is rarely caused by one single thing. It is usually a combination of growth rate, body weight, nutrition, limb loading, exercise, and footing.

Rapid Growth

Fast growth increases stress on immature cartilage and bone. The bigger and heavier the foal becomes before the growth plate is ready to tolerate that load, the more likely inflammation becomes.

This is why physitis is often seen in large, heavy, well-muscled, fast-growing foals.

Excess Energy Intake

A foal receiving too many calories may grow faster than the skeleton can comfortably support. This can happen with:

• High-grain diets

• Overfeeding concentrates

• Rich pasture

• Access to the mare’s feed

• Heavy milk production from the mare

• Over-conditioned foals

The problem is not simply “grain is bad” or “milk is bad.” The problem is too much energy relative to the foal’s growth stage, body condition, mineral balance, and workload.

Mineral Imbalance

Growing horses need the right balance of minerals, especially calcium, phosphorus, copper, and zinc. Merck’s nutrition section notes that an imbalanced calcium-to-phosphorus ratio is a potential cause of some forms of developmental orthopedic disease, and copper deficiency may contribute to osteochondrosis or physitis, although research findings are mixed. (Merck Veterinary Manual)

That nuance matters. Throwing random supplements at a foal is not the answer. The diet needs to be assessed properly.

Conformation and Uneven Loading

Foals with angular limb deformities, upright conformation, offset knees, or abnormal hoof balance may overload certain growth plates. This can make swelling more obvious on one side or one limb.

This is also why farrier work is part of physitis management. The foot and limb are not separate conversations. The growth plate has to live with the loading created below it.

Hard Ground and Excessive Exercise

Dry, hard ground can increase concussion through the limbs. Merck notes physitis is often seen during summer when the ground is dry and hard, especially in fast-growing foals. (Merck Veterinary Manual)

Foals do need movement for healthy development, but hard galloping, rough paddock play, forced exercise, or excessive turnout on unforgiving ground can worsen inflammation.

Obesity or Heavy Body Condition

A fat foal is not a healthy foal. Extra weight increases mechanical loading on immature growth plates. This is one of the big mistakes owners make because a big, shiny, chunky foal can look “thriving” while the skeleton is quietly complaining.

Is Physitis the Same as Developmental Orthopedic Disease?

Physitis is considered part of the broader group of developmental orthopedic diseases, often shortened to DOD. DOD is not one disease. It is a cluster of growth-related orthopedic problems in young horses.

Other developmental orthopedic problems include:

• Osteochondrosis

• Angular limb deformities

• Flexural limb deformities

• Subchondral bone cysts

• Growth plate abnormalities

• Some forms of juvenile joint disease

Merck notes that physitis can occur along with osteochondrosis, which is why vets may recommend radiographs rather than assuming the swelling is simple growth plate inflammation. (Merck Veterinary Manual)

Is Physitis Painful?

It can be. Mild physitis may cause swelling with little obvious discomfort. More significant cases can be warm, tender, stiff, and lame.

Pain matters because pain changes limb use. A foal that is sore may stand abnormally, shift weight, move less, or develop secondary problems such as flexural changes. Merck notes that pain from physitis or other orthopedic disease can contribute to acquired flexural deformities, where young horses begin to walk more on their toes or develop a more upright foot. (Merck Veterinary Manual)

So no, physitis should not be ignored just because the foal is still moving around.

Severity and Risk Framework

Mild Physitis

Mild physitis may look like firm, mild swelling around both fetlocks or knees. The foal is bright, eating or nursing normally, not feverish, and either sound or only slightly stiff.

What to do: arrange a veterinary check, review the diet, assess body condition, monitor swelling, and reduce excessive loading. Mild cases often respond well when caught early.

Moderate Physitis

Moderate physitis may involve obvious swelling, warmth, mild to moderate lameness, stiffness, or reluctance to move. The foal may still be bright, but the swelling is more than a minor cosmetic change.

What to do: veterinary assessment is needed. Radiographs may be recommended, and management usually includes diet correction, controlled exercise, soft footing, farrier care, and monitoring.

Severe Physitis

Severe physitis may cause marked swelling, obvious pain, significant lameness, rapid worsening, or developing limb deviation.

What to do: treat this as urgent. The concern is not just discomfort today. The concern is damage to a growth plate that may affect limb development and future soundness.

Critical: Possible Infection or Joint Disease

This is the category owners must not miss.

Red flags include:

• Sudden severe lameness

• Fever

• Depression or dullness

• Not nursing or eating

• One very swollen or painful limb

• A hot, swollen joint

• Wound near a joint or growth plate

• Multiple swollen joints

• Very young foal with lameness

• History of poor colostrum intake, sepsis, navel infection, diarrhea, or illness

Foals can develop septic arthritis, septic physitis, and osteomyelitis, which are infections involving joints, growth plates, or bone. Merck describes septic arthritis in foals as sometimes involving osteomyelitis of the adjacent growth plate, and treatment may require systemic and local antimicrobials plus flushing of infected joints. (Merck Veterinary Manual)

This is not a “watch it for a week” situation. A lame, feverish, dull, or systemically unwell foal needs urgent veterinary care.

What Else Can Look Like Physitis?

Not every swollen area near a young horse’s joint is simple physitis. Important rule-outs include:

Septic Arthritis or Septic Physitis

This is one of the most important differentials. Infection in a joint, growth plate, or bone can permanently damage the limb and can be life-threatening, especially in young foals. PubMed-reviewed veterinary literature describes septic arthritis, physitis, and osteomyelitis in foals as serious conditions where aggressive local therapy, lavage, debridement, and antimicrobial therapy may be needed. (PubMed)

Osteochondrosis

Osteochondrosis is another developmental orthopedic disease involving abnormal cartilage and bone development. It may cause joint swelling, stiffness, lameness, or radiographic changes. Merck notes that osteochondrosis can be associated with rapid growth, high carbohydrate diets, mineral imbalance, and biomechanical factors. (Merck Veterinary Manual)

Angular Limb Deformity

Foals with crooked limbs may place uneven stress on the growth plates. Physitis may develop alongside or secondary to that uneven loading.

Flexural Limb Deformity

A foal walking more upright, on the toes, or developing a club-like foot may have pain-driven flexural changes. Physitis can be part of that pain picture. (Merck Veterinary Manual)

Trauma or Fracture

A kick, fall, paddock injury, or mare stepping on the foal can cause swelling and lameness. Sudden one-sided pain should not be assumed to be developmental.

Joint Effusion

Fluid inside a joint can look like swelling near a growth plate, but the significance is different. Joint swelling may point toward osteochondrosis, trauma, or infection.

How Do Vets Diagnose Physitis?

Diagnosis starts with a proper physical and lameness examination.

Your vet may assess:

• Age and growth stage

• Which growth plates are swollen

• Whether swelling is symmetrical or one-sided

• Pain on palpation

• Lameness severity

• Limb conformation

• Hoof balance

• Body condition

• Diet and feeding history

• Pasture quality

• Turnout and exercise

• Ground conditions

• Fever or signs of systemic illness

Radiographs are commonly used to assess growth plates and rule out other problems. Merck notes that radiography aids clinical assessment in physitis and can show the boxy appearance around affected growth plates. (Merck Veterinary Manual)

If infection is a concern, your vet may recommend bloodwork, joint fluid sampling, ultrasound, culture, or hospital referral. This is especially important in foals with fever, marked pain, sudden lameness, or a history suggesting poor passive transfer or neonatal illness.

How Is Physitis Treated?

Treatment depends on severity, age, cause, and whether infection or another orthopedic disease has been ruled out.

Correct the Diet

This is usually the central part of treatment.

The aim is not to starve the foal. The aim is to slow excessive growth and correct nutritional imbalance while still supplying the nutrients needed for healthy bone development.

Your vet or equine nutritionist may recommend:

• Reducing calorie intake

• Removing or reducing grain and high-starch feeds

• Stopping the foal from stealing the mare’s hard feed

• Changing from rich forage to more moderate grass hay where appropriate

• Using a ration balancer instead of a high-energy concentrate

• Correcting calcium, phosphorus, copper, zinc, and overall mineral balance

• Monitoring body condition and growth rate

AAEP describes feeding young horses as a balancing act because the foal’s nutritional start can influence long-term health and soundness. (AAEP)

In some cases, early weaning may be discussed if the mare is producing a lot of milk and the foal is growing too rapidly. That should be a veterinary decision, not a reflex move.

Control Exercise

Inflamed growth plates need less concussion and less uncontrolled loading.

Management may include:

• Stall rest or a small yard

• Soft, safe footing

• Avoiding hard, dry, compacted ground

• Avoiding forced exercise

• Avoiding rough play with larger or more active horses

• Gradual return to normal turnout as swelling and lameness improve

Merck recommends restricting exercise to a yard or large, well-ventilated loose box with a soft surface as part of physitis treatment. (Merck Veterinary Manual)

Improve Foot Balance

Hoof trimming matters. A long toe, uneven medial-lateral balance, or poor limb loading can increase stress on growth plates.

Your vet and farrier should work together, especially if there is limb deviation, upright conformation, or uneven swelling. Merck includes careful, frequent hoof trimming as part of physitis treatment. (Merck Veterinary Manual)

Pain Relief When Needed

Some foals need veterinary-prescribed anti-inflammatory medication. Do not give human pain medication, leftover horse medication, or random doses without veterinary direction. Foals are not small adult horses, and dosing mistakes can cause real harm.

Monitor Progress

Mild cases may improve over several weeks once nutrition and loading are corrected. More significant cases need repeat checks, especially if swelling, lameness, or limb shape is not improving.

A useful monitoring plan includes:

• Weekly photos from the front, side, and behind

• Body weight or weight tape tracking

• Body condition scoring

• Feed diary

• Growth changes

• Lameness notes

• Farrier updates

• Vet recheck timing

This is where owners can genuinely help. Good records make patterns much easier to see.

When Is Physitis an Emergency?

Physitis itself is not always an emergency, but swelling around a foal’s joints or growth plates can be an emergency if infection, fracture, severe pain, or systemic illness is possible.

Call a vet urgently if:

• The foal is suddenly lame

• The foal has a fever

• The foal is dull, depressed, or not nursing

• One limb is much worse than the others

• The swelling is rapidly increasing

• The area is very hot or painful

• There is a wound near a joint or growth plate

• The foal is younger than a few months and acutely lame

• Multiple joints or limbs are swollen

• The foal has diarrhea, navel infection, or signs of sepsis

• The foal cannot keep up with the mare

• The limb is becoming crooked or more upright

The University of Minnesota notes that joint infections can be life-threatening and should be treated early and aggressively, with foals often running a fever before obvious lameness or joint swelling appears. (University of Minnesota Extension)

That is the bit that catches people out. A foal can look “a bit off” before the limb looks dramatic.

What Should You Do Next?

If you notice swelling around a foal’s growth plates:

1. Stop guessing from the paddock fence. Look closely at both limbs and compare left to right.

2. Check the foal’s attitude. Bright and nursing is less concerning than dull, febrile, or not eating.

3. Assess lameness. Any obvious lameness deserves veterinary assessment.

4. Check temperature. Fever changes the urgency.

5. Review the diet. Look at grain, pasture, mare feed access, body condition, and supplements.

6. Reduce hard exercise. Use soft, controlled turnout or confinement as advised.

7. Call your vet. Especially if swelling is painful, one-sided, severe, worsening, or associated with illness.

8. Do not add random supplements. Balance the ration properly instead.

9. Get radiographs if recommended. They help rule out more serious orthopedic disease.

10. Plan rechecks. Physitis is managed over time, not fixed in one afternoon.

Common Mistakes Owners Make

Assuming It Is Just Growing Pains

Some mild cases are manageable, but growth plate swelling still deserves attention. Waiting until the foal is obviously lame can make management harder.

Overfeeding a “Good Doer” Foal

A chunky foal may look impressive, but excess body condition increases loading on immature limbs.

Blaming Protein Alone

Protein often gets blamed, but the bigger issue is usually total energy intake, growth rate, mineral balance, body condition, and limb loading. Protein still matters, but it is not the whole story.

Adding Supplements Without Analysing the Diet

More minerals are not automatically better. Calcium, phosphorus, copper, zinc, and other nutrients need balance. Random supplementation can make a ration more unbalanced.

Keeping the Foal on Hard Ground

Hard, dry ground increases concussion. If the foal is sore and inflamed, footing matters.

Ignoring One-Sided Painful Swelling

One-sided, painful swelling should raise suspicion for trauma, infection, or focal orthopedic disease. That is not the same as mild symmetrical developmental swelling.

Forgetting the Farrier

Foot balance affects limb loading. A physitis plan without hoof assessment is only half a plan.

Can Physitis Be Prevented?

Not every case can be prevented, especially where genetics, conformation, or rapid natural growth are involved. But risk can often be reduced.

Prevention focuses on steady growth, not maximum growth.

Useful steps include:

• Feed for controlled, even growth

• Avoid overfeeding grain and concentrates

• Prevent the foal stealing the mare’s hard feed

• Use forage appropriately

• Balance minerals properly

• Monitor body condition

• Avoid obesity

• Provide regular farrier care

• Manage turnout on safe footing

• Avoid excessive hard-ground exercise

• Watch heavy, fast-growing foals closely

• Record changes in limb shape early

Merck specifically advises monitoring older foals and yearlings that are fat or heavily muscled, especially when ground is hard and dry, and restricting feed and exercise when those risk conditions are present. (Merck Veterinary Manual)

FAQ

Can physitis go away on its own?

Mild physitis may improve with better nutrition, reduced loading, soft footing, and time. But it should still be assessed because swelling around a growth plate can also occur with more serious developmental disease or infection.

Should I stop feeding my foal grain?

Do not make extreme diet changes without advice. Many foals with physitis need reduced energy intake, but they still need appropriate protein, minerals, and vitamins for healthy growth. The goal is balance, not starvation.

Is physitis caused by too much protein?

Not usually by protein alone. Physitis is more often linked with rapid growth, excess calories, body weight, mineral imbalance, conformation, hard ground, and exercise. Protein may be part of the ration review, but it is rarely the whole story.

Do foals with physitis need x-rays?

Often, yes. Radiographs help confirm the growth plate changes and rule out other problems such as osteochondrosis, fracture, infection, or limb deformity. They are especially important if the foal is lame, painful, one-sided, or worsening.

Is physitis dangerous?

Mild cases can resolve well if managed early. Severe, persistent, painful, infected, or one-sided cases can affect growth and future soundness. The danger is not the word “physitis” itself. The danger is missing the cases that are more than simple growth plate inflammation.

Final Thoughts

Physitis is common in growing horses, but common does not mean harmless. It is a sign that the growth plate is under stress.

The most important steps are to recognise swelling early, assess the foal’s comfort and overall health, review the diet properly, manage exercise and footing, correct hoof balance, and involve your vet before the problem becomes more serious.

A foal does not need to be pushed to grow as fast as possible. The aim is steady, balanced, sound growth. Big and shiny is nice. Big, shiny, and lame is not the dream.

If your foal has swollen growth plates, stiffness, lameness, or you are unsure whether the diet is helping or hurting, ASK A VET™ can help you work through the signs, urgency, and next steps with practical veterinary guidance.