Squamous Cell Carcinoma in Donkeys

Squamous cell carcinoma, often shortened to SCC, is a malignant cancer that starts in squamous cells. These cells line the outer skin and many moist body surfaces, including the eyelids, third eyelid, genital tissues, and parts of the mouth. In donkeys, SCC has been recorded in cutaneous, ocular, and genital forms, and current donkey references advise investigating and treating it much like SCC in horses and ponies.

In practical terms, SCC often begins as a small irritated-looking patch, plaque, wart-like growth, or ulcer that does not heal. Over time it may become raised, crusted, bleed easily, or develop a cauliflower-like appearance. Some tumors stay fairly localized at first, but they can invade nearby tissue and become harder to remove if care is delayed.

Many donkey cases are first noticed around the eye or eyelid, on lightly pigmented skin, or on genital tissues. These locations matter because even a small tumor can interfere with vision, comfort, urination, breeding, or normal skin function. That is why a persistent sore or mass in these areas deserves a prompt exam by your vet.

SCC develops when squamous cells become cancerous. In donkeys, the exact trigger for any one case is not always clear, but the best-supported risk factors come from equine medicine and donkey references. Ultraviolet radiation is considered an important risk factor, especially for ocular and periocular SCC, and tumors are reported more often in lightly pigmented or nonpigmented tissues.

That means donkeys with pink or lightly pigmented eyelids, muzzle skin, genital skin, or other sun-exposed areas may be at higher risk over time. Chronic sun exposure is especially relevant for animals living outdoors year-round, in southern climates, or at higher altitude where UV intensity can be greater.

For genital SCC, chronic irritation may also play a role. In horses, SCC of the penis and prepuce has been associated with smegma-related irritation and may arise from or resemble papillomatous lesions. Donkey texts recommend managing suspected SCC as in horses and ponies, so your vet may consider these same risk patterns when evaluating a lesion.

Age can matter too. SCC is seen more often in older equids, although it is not limited to seniors. Because donkeys often hide problems under a dense coat and may be examined less often than horses, some tumors are found later than ideal.

Diagnosis starts with a careful physical exam and a close look at the lesion's location, size, depth, and surface. Your vet will usually want to know how long the area has been present, whether it has changed quickly, and if there has been bleeding, discharge, eye irritation, or trouble urinating. Because SCC can mimic proud flesh, habronemiasis, papillomas, sarcoids, or chronic wounds, appearance alone is not enough for a confident diagnosis.

A biopsy with histopathology is the usual way to confirm SCC. Small masses may sometimes be removed completely and submitted, while larger or more delicate lesions often need an incisional or punch biopsy first. Cytology can occasionally help, but tissue biopsy gives the clearest answer and helps guide treatment planning.

Your vet may also recommend staging tests to look for local spread. Depending on the site, this can include palpation or sampling of nearby lymph nodes, ultrasound, radiographs, or advanced imaging if invasion into deeper tissues is a concern. Around the eye, imaging may be needed if the tumor could extend into the orbit. For genital tumors, your vet may assess inguinal or sublumbar lymph nodes and evaluate how deeply the mass extends before discussing surgery or other options.

Because early tumors are usually easier to manage, it is worth investigating suspicious lesions sooner rather than waiting to see if they resolve on their own.

Not every case can be prevented, but risk reduction is still worthwhile. Because ultraviolet exposure is an important risk factor for equine SCC, practical sun protection matters most for donkeys with pink or lightly pigmented eyelids, muzzle skin, genital skin, or other sparsely pigmented areas. Shade, turnout planning, and UV-protective fly masks can help reduce exposure, especially during strong sun.

For donkeys with eye-area risk, ask your vet whether a UV-blocking fly mask is appropriate. Evidence in equids supports UV exposure as a risk factor, even though the exact preventive effect of masks has not been fully quantified. In real-world management, reducing sunlight to vulnerable tissues is still a sensible step.

Routine hands-on checks are also important. Donkeys can hide skin disease under a dense coat, and small lesions may be missed until they are advanced. Check the eyelids, third eyelid area, muzzle, sheath, penis, vulva, and inguinal region regularly for sores, plaques, crusts, or masses that do not heal.

Good hygiene and prompt veterinary attention for chronic irritation may also help, particularly around genital tissues. If your donkey has a persistent wound, recurrent inflammation, or a wart-like lesion that changes over time, have your vet examine it early rather than waiting. Early recognition is one of the most practical forms of prevention against more serious disease.