High severity

Bog spavin (Tarsocrural effusion)

Bog spavin is a soft, fluid swell of the tarsocrural (hock) joint — tarsocrural effusion — not bone spavin (osteoarthritis of the lower hock), not a capped hock, not thoroughpin, not windpuffs, not osselets in the fetlock, and not ringbone in the pastern. A photograph cannot diagnose bog spavin. A still cannot tell bog spavin from bone spavin, a capped hock, thoroughpin, windpuffs, or an infection in the hock. Diagnosis is a vet exam. The conformation scan is a first look at the hock swell, not a verdict that your horse has bog spavin, and there is no bog-spavin scanner.

Symptoms to watch for

A soft, fluid swell on the front or inside of the hock (the tarsocrural joint), not a hard bony bump lower on the hock

Heat, filling, or pain over the hock (an active, inflamed joint), or a cool, soft swell that has been there a while

A shorter stride, especially after work or on circles

Reluctance to flex that hock, land, or work on that limb

Hock swelling that can look like bone spavin, a capped hock, thoroughpin, windpuffs, or an infection in the hock

Some horses stay even at walk; the first sign is a soft hock swell after work — a reason to book a vet, not a photo verdict

Common causes

Tarsocrural (tibiotarsal) joint effusion — extra synovial fluid in the hock joint
OCD, trauma, or strain of the hock — the history is a clue, not a diagnosis
Not bone spavin (osteoarthritis of the distal intertarsal / tarsometatarsal joints), not a capped hock, not thoroughpin, and not windpuffs
Not osselets (fetlock traumatic arthritis), not ringbone (pastern osteoarthritis), and not a septic hock — a still cannot tell bog spavin from those, and those need a vet

Prevention

Warm up before hard work and build hock-heavy work gradually
Match the work to the footing — avoid sudden heavy or fast work on hard ground
Watch the hock for a new soft swell, heat, or filling and rest rather than working through it
Do not treat a photo, a hock swell, or a scan result as a diagnosis
Conformation photos can help you and the vet look at the hock swell — they do not confirm or rule out bog spavin, and they cannot tell bog spavin from bone spavin, a capped hock, thoroughpin, windpuffs, or an infection in the hock

What to do

1
Book a vet visit if you find a soft swell on the hock, heat, or filling. Diagnosis is a vet exam — not a photograph.
2
Stop work. Rest the horse and do not ride through a hot, painful hock swell hoping it will settle.
3
Photograph the hock swell in good light and keep it on the horse's record so you and the vet can see change over time — a first look to share, not a diagnosis.
4
Use a conformation scan only as a first look at the hock swell to share, not as a bog-spavin test. There is no bog-spavin scanner.
5
If bog spavin (tarsocrural effusion) is confirmed, follow the plan your vet prescribes — that may include rest, controlled exercise, or further imaging. Do not start a treatment protocol from a photo.
6
Keep the vet on the same page. Share what you see; do not treat a photo as a verdict.

When to call the vet

Pick up the phone if…

Schedule a vet visit if you find a soft swell on the hock, if the swell is hot or painful, if the horse is short on that limb, or if filling appears after work. Call sooner if the horse will not bear weight, the limb is suddenly very swollen, or the horse is dull or off feed. A photograph cannot diagnose bog spavin. A still cannot tell bog spavin from bone spavin, a capped hock, thoroughpin, windpuffs, or an infection in the hock. Diagnosis is a vet exam. The conformation scan is a first look at the hock swell, not a verdict, and there is no bog-spavin scanner.

Get a first look at the hock swell

Scan conformation in HorseCare. 5 free scans this month, then Pro.

Scan conformation

5 free scans this month, then Pro. Scans run in the HorseCare app.

Educational content only. Not a substitute for veterinary advice.