Fibrotic Myopathy in Donkeys: Abnormal Gait, Muscle Scarring & Care

Fibrotic myopathy is a condition where part of a donkey's hind-limb muscle heals with dense scar tissue instead of normal flexible muscle fibers. In equids, this most often affects the hamstring group in the back of the thigh, especially the semitendinosus and semimembranosus muscles. As that scar tissue tightens, the muscle cannot stretch and shorten normally, so the leg moves in a very characteristic, mechanical way.

Many pet parents first notice an unusual gait rather than obvious pain. The hind leg may swing forward, then snap backward right before the hoof touches down, creating a stiff or slapping step. This pattern is often easiest to see at the walk. Some donkeys also develop a visible dip, firm band, or muscle loss over the back of the thigh.

Although most published veterinary information comes from horses, the same anatomy and injury pattern apply to donkeys. The condition can range from mild and mostly cosmetic to severe enough to limit work, exercise, or comfort. The good news is that some donkeys remain comfortable long term, especially when the problem is stable and your vet helps match care to your donkey's daily needs.

The most common cause is trauma to the hamstring muscles. A donkey may slip, overextend the hind limb, get the leg caught, kick out forcefully, or strain the muscle during fast turns or rough footing. When the muscle tears, the body repairs the area with scar tissue. If that scar becomes dense and contracted, normal motion is lost and the classic gait appears.

Repeated strain can also contribute. In equids, fibrotic myopathy has been linked to athletic overuse, abrupt turns, sliding stops, and other movements that overload the caudal thigh muscles. Donkeys used for packing, pulling, breeding, or uneven-terrain work may be at risk if conditioning, footing, or hoof balance are poor.

Less common causes include intramuscular injections placed into the hamstring region, especially if the medication is irritating to tissue, and congenital or developmental abnormalities reported in some equids. In practice, your vet will also consider look-alike problems such as upward fixation of the patella, stifle disease, neurologic disease, hoof pain, or other muscle disorders before deciding scar tissue is the main issue.

Diagnosis usually starts with a hands-on lameness exam. Your vet will watch your donkey walk and turn, then feel the muscles of the upper hind limb for a tight band, dimpling, pain, or muscle loss. In many chronic cases, the gait pattern plus palpation findings are strongly suggestive of fibrotic myopathy.

Ultrasound is often the most practical next step because it can show torn muscle fibers, scar tissue, and the extent of the lesion. Radiographs may be added if your vet wants to look for mineralization or rule out bone and joint problems. In selected referral cases, more advanced imaging or even biopsy may be discussed, especially if surgery is being considered or the diagnosis is unclear.

Because donkeys can mask discomfort and may move differently than horses, it is important not to assume every stiff hind-leg gait is fibrotic myopathy. Your vet may also check the hoof, hock, stifle, pelvis, and neurologic function. That broader approach helps avoid missing another treatable cause of lameness.

Not every case can be prevented, because accidents happen. Still, you can lower risk by focusing on safe footing, gradual conditioning, and good hoof balance. Donkeys asked to work on uneven ground, turn sharply, carry loads, or play hard after time off are more likely to strain the upper hind-limb muscles when they are unfit or moving on slippery surfaces.

Warm-up and cool-down matter, especially for athletic or working donkeys. Sudden bursts of effort with tight, cold muscles increase the chance of tearing. Regular trimming also helps support normal limb mechanics, which may reduce abnormal strain higher up the leg.

Injection technique matters too. Hamstring muscles are a poor choice for intramuscular injections when other safer sites are available, and irritating medications should never be placed intramuscularly unless your vet specifically directs it. If your donkey has a fresh hind-limb injury, early veterinary guidance may help limit inflammation, support healing, and reduce the chance that a muscle tear matures into dense scar tissue.