EQUINE DERMATOLOGICAL PRACTICE TIPS

Robert M. Miller, DVM

Equine Sarcoid A number of efficacious treatments

are now available to treat the common, dry, flat, verrucous sarcoids. These gray skin tumors must be differentiated from papil- lomas, and mycotic lesions. They respond to cryosurgery, to heat (the Thermaprobe ® instrument), to topical podophyllin, and to injections of mycobacterial emulsions, an immunogenic agent (Ribigen ®, Ribi Immuno Chem Research). However, for many years I have prescribed topical flu- orouracil cream (Efudx 0.5 % topical cream, Ciba Pharmaceuticals) with consistent success. The treatment is simple and rela- tively inexpensive, although slow. The owner must be warned to wear disposable surgical gloves because this anti-cancer drug is irritating to the skin. A small amount of the cream is applied to the sarcoid, once daily, without rubbing it in, for 30 days. There will be an inflammatory reaction. I examine the lesion 60 days after the initial visit. If any islands of tumor tissue are still visible, I prescribe re-treatment of those areas for an additional 2 weeks. Once healed, there is no evidence of the original lesion, but the site will be hairless. If this is of cosmetic concern in show horses, the hairless area may be excised surgically without the risk of recurrence of explosive granulomatous sarcoid, which so often follows excision of an untreated tumor.

Author's address: 320 Carlisle, Thousand Oaks, CA 91361

These unszgnuy, hart] noomes, usu- ally varying from pea to walnut size, are commonly found under the saddle and girth area. They must be differentiated from neoplasms, parasitic cysts (warbles), foreign bodies, and "sit fasts." If neglected, they become painful, and the surface may ulcerate due to pressure necrosis from the saddle. I believe that the cause of these nodules is heat and friction on insect bites in horses with highly reactive skin. They respond partially to corticosteroids applied topically (especiallyifmixed with DMSO), or injected. It is, however, extremely diffi- cult to inject liquids into these very hard nodules.

I had some success years ago using a dental syringe with a luer-lock hub and a high pressure crutch-type plunger. But for at least 15 years, I obtained dramatic re- sponses by injecting long-acting cortico- steroids with the DermoJect instrument. This instrument was designed to inject human skin without a needle, using an extremely fine jet propelled by a very high air pressure (available from Robbins, Inc., Chatham,N J). The instrument is expensive (several hundred dollars), but easily pen- etrates the lesions of nodular necrobiosis.

I shave and surgically prep the le- sions. If the medication to be used is diluted with lidocaine, it will eliminate the slight stinging sensation caused by the injec- tions, and the diluted preparation will be less likely to clog up the fine pore through which it is propelled. Each nodule should receive multiple injections. I recommend no saddle be used on the horse for 30 days, at which time I re-examine the patient. (Bareback riding is allowed after 3 or 4 days.) Typically,almond-sizednoduleswill have shrunken to the size of a grain office. If larger, they should be injected again, and a final examination done a month later. In

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biosis will probably develop future lesions if precautions are not taken. In my experi- ence such lesions develop at new sites rather than at those previously treated.

Prevention of nodular necrobiosis requires good management. Insect bites under the saddle area can be minimized with insect repellants and the use of day sheets or other blankets which can deflect and protect against insectbites. Care should be taken not to allow saddle or girth pressure over a wheal, by using padded tack. Weals should be treated early to obtain swift remission. Saddles should be well-fitted (many are not) and I have observed that saddle blankets and pads made of real animal hair (sheared wool, woven wool, or hair felt) are much less likely to cause back problems than synthetic materials, probably because they are cooler.

Grease Heel ("Scratches") The idea for this compound came

from an informal conversation with two rural North Carolina practitioners in the hotel bar at an AAEP meeting several years ago.

Take a one pound jar of Morumide ~ or Furacin ® ointment, add a heaping tablespoon of Dexamethasone oral pow- der (Azium) and two tablespoons of povidol iodine ointment (Betadine).

Warm gradually in microwave oven or hot water bath until the ingredients are melted. Stir and allow to cool. Apply to the lesions once daily, preferably under a bandage. I have found the response to be quite dramatic.

Fly Bi tes Fly bites can be prevented by elimi-

nating flies, a task not easily accomplished. I found that I could dramatically reduce

72 EQUINE VETERINARY SCIENCE

the population of manure breeding stable flies on my farm, and on many clients farms, with the use of Fly Predators. These tiny, harmless insects spend their entire life near the surface of manure, parasitiz- ing the larvae of horse of house and stable flies. It is a biological control program which costs no more than an effective chemical control program. The environ- ment is not chemically contaminated. Several companies supply Fly Predators. I get mine from Spalding Laboratories, 760 Printz Road, Arroyo Grande, CA 93420. They send me a monthly package of Fly Predator larvae in the mail during fly season (fly season lasts 9 months in Southern California). When flies are con- trolled, a host of associated skin diseases will be eliminated. These include allergic dermatitis, atopy, corynebacterium and other infections, and self-inflicted trauma from stamping and kicking at flies, such as

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shoe-boils and belly abscesses. Other flypest-caused problems in horses include summer-sores, eye infections, wound in- fections, and weight loss.

Saddle Sores The cause of sores under the saddle

area is usually ill-fitting or inadequate saddles or padding. However, poor riding technique is a contributing factor, as is failure to properly clean the back before saddling, and failing to periodically cool the back and relieve saddle pressure on long tides.

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Material for Talking it Over is not reviewed or refereed. Manu- scripts may be on any topic of interest to veterinarians and should be submitted to Journal of Equine Veterinary Science, P.O. Box 1209, Wildomar, CA 92395

The best way to heal a sore is not to ride the horse. Second best, the horse may be able to be ridden bareback, or with a surc- ingle and pad. However, if the need for the horse precludes these approaches, try cut- ting a hole in a felt saddle pad slightly larger than the sore, and directly over the sore. Fill the hole with a talcum-based antiseptic powder (baby powder or Columbia Anti- septic Powder~). Talc mixed with a small amount of zinc oxide powder also works well. Next, put a second felt pad over the ftrst one. Add a blanket, if desired, and, finally, the saddle. Wash the back after riding.

Sunlight-induced Squamous Cell Carcinoma

Horses which have unpigmented skin which is not protected by adequate hair cover often develop squamous cell carci- noma some time after middle age. The most common sites are the eyelids, the mem-

Volume 11, Number 2, 1991 73

brana nictitans, the cornea, the perineum, and the preputial area in males. Paint and Pinto horses are commonly affected as are Appaloosa, P. O. A. ponies, andbald-faced horses of ordinary colors. Albino horses, of course, are especially susceptible.

Very early diagnosis usually offers a favorable prognosis. Any ulcerated lesion or chronic sore in an unpigmented, thinly haired site should be immediately biopsied. Smaller lesions, including those of the cornea, respond extremely well to cauter- ization with the HyFrecator. Since 1958, I have used a Birtcher HyFrecator for this purpose on dozens of horses and hundreds of Hereford cattle with an extremely high success rate.

Larger lesions respond to injections of Ribigen ® (Ribi ImmunoChem Re- search, Inc., Hamilton, Montana) very nicely. Of course, squamous cell carci- noma also responds to radiotherapy, and

we've had some success with the Therma- probe.

Obviously this kind of skin cancer is preventable, if one can eliminate or mini- mize the effects of direct or reflected sun- light on susceptible areas. Most horse own- ers will comply with the recommendation when we explain the susceptibility of the horse. Some of the methods used are listed below.

1. Confining the horse to a stall or shaded area during daylight hours, except when being ridden.

2. Tattooing the unpigmented skin. Unfortunately, this is not apermanent solu- tion and it must be periodically repeated.

3. The use of mascara and/or eye makeup around the eyes.

4. The use of sunscreening prepara- tions on areas other than the eye, such as the perineum or prepuce.

5. Dying the involved area weekly

with a dark dye such as the dark blue "pink eye" formulations marketed for cattle.

6. Protecting the eyes with tinted goggles. (Racing or trailering goggles may be equipped with appropriate lenses.)

7. The new fly masks being marketed to protect horses eyes from flies also sig- nificantly shade the face. Horses can even be ridden while they are wearing these masks because they can see through the mesh. For horses with unpigmented eye- lids, the sun protecting value of these masks is more important than their insect protect- ing value. Further protection can be ob- tained by sewing a solid strip of fabric to the mask above the eyes, providing avisor- like effect. Preventive measures should be started early in the horse's life. A lethal does of cumulative solar radiation may be acquired by a weanling while it is growing up in a pasture, even though the actual neoplasm may not manifest itself until much later in life.

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74 EQUINE VETERINARY SCIENCE