Maximizing Diagnostics for Equine Skin Conditions

This article originally appeared in the Spring 2026 issue of EquiManagement. Sign up here for a FREE subscription to EquiManagement’s quarterly digital or print magazine and any special issues.

During her presentation at the 2025 American Association of Equine Practitioners Convention, Julia Miller, DVM, DACVD, from the ­Animal ­Dermatology Clinic in Louisville, ­Kentucky, gently and humorously reprimanded equine veterinarians for their diagnostic shortfalls when faced with equine dermatologic conditions. “We don’t guess; we’re scientists,” she stated.  

Miller then offered clinical takeaways and words of wisdom for improving stallside diagnostic skills to prioritize differentials and guide appropriate treatment. 

History Is Critical

“History is critical when evaluating dermatologic patients … it is a diagnostic!” she said. “Is the horse pruritic in the warm or cold months? If it’s during the warm months, then differentials include Culicoides or other flying insects or atopy. But if it’s during the colder months, then pediculosis is more likely.”  

Were there lesions before the pruritus (if yes, then think pemphigus), and what were the changes in the horse’s feed or environment?

Physical Exam Tips

Next, perform a physical exam looking for clues such as papules, pruritus, ectoparasites, crusts, erosions, ulcerations, and alopecia. Only rarely will the horse present with pustules. 

“If at first you don’t succeed, you missed something. Do more diagnostics,” Miller implored, pointing out that a good microscope is a veterinarian’s best friend. But only if you take good care of it with routine cleanings and annual professional servicing. 

“We don’t actually need that many diagnostic tools,” she said. “Scotch tape, slides, cannisters or red top tubes for crusts, a toothbrush, swabs, a scalpel blade, and mineral oil, lens cleaner, and Kimwipes.”

Skin Scrapings

Emphasizing the importance of skin scrapings, Miller presented Kris Kringle, a 4-year-old Clydesdale that was stamping his hind limbs excessively and biting. No other horses on the farm were affected. 

“All Clydesdales have Chorioptes bovis in their feathers. It’s not about cure, just maintenance,” Miller said. 

She reminded practitioners that C. bovis is a superficial parasite, so after ­clipping the feathers, scrape the skin but not down to bleeding. This parasite can be difficult to find, and cases can be asymptomatic. Not all horses present with crusty lesions, and even Miller has had to biopsy to find them.

When looking at skin scrapings under the microscope, Miller advised against staining the scrapes and recommended closing the iris diaphragm to reduce light passing through, making it easier to see parasites. “They’re huge, so scan the slide at 4x,” she said.  

Acetate Tape Impressions

Performing impression cytology looking for Staphylococcus spp. can be unrewarding. But acetate tape impressions are excellent for ectoparasites such as lice and Chorioptes, as well as bacterial pyoderma and Malassezia.

“Find a new crust, get the crust off, pinch the skin, then press the microscope slide on the skin. Alternatively, you can swab with a cotton tip applicator and roll onto a slide,” said Miller. 

She then recommended staining with Diff-Quik (skip the blue fix if staining tape). Start scanning at 4x, then increase the power as needed. 

As an example, Miller presented Dreidel, a 12-year-old Quarter Horse with lesions on his ears and pruritus. The impression cytology revealed ­Staphylococci—bacteria commonly seen secondary to atopy, which was consistent with this particular horse’s history. Allergy testing was also performed. 

Fine-Needle Aspirates

Turning to fine-needle aspirates (FNAs), Miller emphasized that this diagnostic is not just for tumors.

“If you have a dermatologic condition that is creating papules and nodules, then consider an FNA,” she said. “Use either the suction technique or woodpecker, and you can use a 25-gauge needle. It gets you plenty of material. Then either stain with Diff-Quik or send out to the lab.”  

As an example, Miller described a gelding with acute onset generalized nodules on a swollen sheath. The FNA revealed all lymphocytes, and she diagnosed lymphoma, following up with biopsy. As a second example, she presented a case with persistent nodules on the chest that improved in the winter months. FNA revealed eosinophilic granulomas.

“You can also biopsy these, but FNA is much cheaper and does not require sedation,” said Miller. 

Trichography

Trichography, or hair evaluation, can be performed to diagnose ectoparasites (lice), hair shaft abnormalities, and dermatophytosis, the latter of which is very rare. 

“Gently pluck and put the hairs in a red top tube immediately, because hair will blow away or get dusty,” Miller advised.  

Bacterial Culture and Sensitivity Testing

For bacterial culture and sensitivity, be sure you always perform cytology first (like an impression smear or swab to evaluate in-house) to prove it’s a bacterial infection. Aerobic cultures are needed more than 99% of the time, and cultures are indicated if the horse has not responded to one course of antibiotic. Multi-drug-resistant Staphylococcus aureus is common and a public health concern.

“Take cytology and culture swab at the same time so you don’t need to go back to the farm,” said Miller. “And don’t swab the distal limb willy-nilly—you’ll culture poop and grow a lot of fun stuff that doesn’t ­matter. Instead, make sure to swab under an affected crust.” 

Skin Biopsies

Finally, skin biopsies should be performed to diagnose vasculitis, autoimmune conditions, deep infections, and neoplasia. 

“These must be sent to an equine dermatopathologist. It is a very specialized test! And please send a thorough history and good pictures. A description of ‘chronic dermatitis’ is not a good history,” Miller emphasized.

 She then suggested the following do’s and don’ts for performing biopsies:

• Do not surgically clip and scrub. Send the crusts.
• Perform a local block (e.g., lidocaine and bicarbonate).
• Biopsy three to five distinct sites.
• A 6 millimeter biopsy punch is a standard size.
• Biopsy the lesion! Do not take the junction of normal/abnormal unless the lesion is an ulcer (this does not apply to tumor biopsies).
• Do not crush samples with forceps.
• Accept that biopsy complications such as dehiscence do occur. 

Final Thoughts

When facing skin issues, particularly chronic ones, “Do not do the same thing over and over,” said Miller. “Do something different.”

Related Reading

• A Systematic Approach to Managing the Pruritic Horse
• Equine Allergy Testing
• Improving the Welfare of IBH-Affected Horses

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