Because so much can go wrong with a horse's skin you may find it difficult to make sense of the physical evidence. However, most of that crusting and oozing, swelling and baldness, actually follows a clear and revealing logic, making it possible for you to track the clues back to the cause. With a grounding in basic dermatological detection, you can solve the crimes perpetrated against your horse's skin by villains within and without.
At the first sign of something amiss with your horse's skin lead him into the sunlight and scrutinize the ailment's characteristics, beginning with its location. "Skin diseases tend to occur in patterns," says William Miller, VMD, professor of veterinary dermatology at Cornell University. "We use the regions of the body and [our] knowledge of the diseases to formulate which [diseases] to consider."
The most commonplace skin problems are on-the-spot responses to mechanical, chemical or bacterial assaults to the outer envelope. If you notice, for instance, that the problem has sprouted up exactly where tack, blanket straps, a detergent-washed saddle pad or some other physical object contacts the horse, you aren't making too much of a leap of judgment in assuming a connection.
Similarly, welts, itchy irritations or scabs on the neck, lower legs and underbelly signal a different sort of contact, this time with biting insects or irritating plants. And skin problems linked to systemic disorders or internal upsets usually afflict predictable body areas--pink, unpigmented skin and the tissues that edge body orifices, for instance.
Now focus in on the hair quality. Whenever the hair is abnormal in appearance, a key distinction to make is whether the skin disorder itself provoked the change or if secondary rubbing is responsible for the damage. Many skin conditions cause mild to maddening itchiness or irritation, which horses try to remedy by biting at themselves or scraping their hide against whatever solid object offers itself as a scratching post.
Observe the horse to see if he passes his private time working to assuage an itch, and check his environment for dander-and-hair evidence that he's rubbing on posts, trees, walls and such. If the hair looks kinky and frayed, or if there's baldness with broken hairs within and surrounding the area, rubbing is probably the cause.
If, on the other hand, a barren spot is neatly defined, with no broken hairs, a skin disorder is the likely cause of the hair loss. When a patch of hair is standing on end ("staring"), the source is probably a substance stiffening on the surface, such as dried secretions or mud, or an enlargement within the skin, such as swelling around the hair follicles. If the horse's entire hair coat is staring, he is suffering from an acute illness or chronic debility.
Identify secretions on the skin. Serum, the same stuff that collects inside unbroken blisters, is distinguishable from sweat by its stickiness and its pale "straw" color. When serum is present, at least the outermost layer of skin has been disturbed. Pus, the product of debris-cleaning white blood cells and whatever garbage they might have scavenged, is a thick, yellowish or greenish glop. Pus is a primary indicator of infection, but it is also part of the cleanup for other tissue insults, such as splinters and burns.
Sebum is a normal, necessary waxy lubricant produced by skin glands and mixed with disintegrating skin cells, but overproduction of this secretion occurs as part of some abnormalities, giving the hair a greasy look and feel. The presence of blood indicates that the skin has suffered a full-thickness insult, whether from the primary condition or secondary rubbing. Dry patches on an otherwise sweaty hide can indicate that local inflammation has impaired sweat-gland function.
Note the characteristics of surface debris and local coloration. Serum dries into colorless crusts or tiny yellow crystals. Dried sebum looks like soggy corn flakes. Blood blackens as it dries. Skin scales and dandruff indicate that keratinization, the multistage process of skin building, has gone wild. Redness of normally pink skin points to inflammation; a purple tint in unpigmented flesh can be a sign of sunburn; white hairs in a normally dark coat indicate pigment-cell damage. Pinprick-sized holes point to feeding insects, while cracks denote severe dryness.
Now give your hands a scrubbing (so you won't introduce additional pathogens), and let your fingers do the walking over your horse's skin. This tactile tour will collect evidence that may not be apparent to your eyes, starting with the truth that some bumps aren't bumps at all, but actually patches of "staring" hair. When swellings are present, palpate their outline. Examine all their subtleties, including their definition (clearly defined, or vaguely outlined?) and shape (flat or mounded tops? Anthill-shaped with sharply sloped sides, or irregularly lumpish?). Manipulate lumps to gauge depth: If the lump moves with the skin, it is located within the skin; if the skin slides around over the lump, the growth is beneath the skin.
Check the consistency of the abnormality: Hardness indicates a long-standing problem, in which fibrous scar tissue or a tumorous growth has developed within or beneath the skin; softness points to a liquid interior. Soft swelling arises from inflammation, with its local increase of blood flow, edema, pooling of lymph between skin cells, or hematoma/seroma (a blood- or serum-filled blister formed in a space within or under the skin).
Each of these swellings responds differently to palpation. Press on the puffy spot with your finger for a few seconds, then release the pressure: Swellings caused by edema retain the imprint and refill slowly (as a marshmallow would under the same pressure); inflammatory swellings and hematomas both rebound immediately, but the latter feel as though they are filled with jelly. Inflammation is triggered by a host of physical, chemical and bacterial skin assaults; edema is usually associated with allergies or hypersensitivity; and hematomas result from "pinch" or "hammer" wounds that don't open the skin so the blood can escape.
Next, pressure-test the trouble spot to check for sensitivity. The degree of added reaction the horse shows is determined in part by the extent and nature of tissue damage and in part by the location of the problem: Areas with little "padding" between skin and bone, such as the face and tail, can be sharply pained by even minor disorders because inflammatory swelling is trapped in a space with little room for expansion.
"If you hit your thigh with a hammer, it would hurt, but not nearly as much as smacking your finger," explains Miller. "When the fluids go to the thigh, there's lots of room. If they go to the finger, they build up and cause pressure." After pressing the suspicious area to test for tenderness, scratch lightly to check for itchiness. If the horse goes into an ecstatic trance and begs for more, he's uncommonly itchy and the abnormality is most likely an allergic or hypersensitivity reaction.
Place your palm over the abnormal area to check its temperature relative to nearby normal skin. Heat indicates inflammation, and palpable warmth associated with a sensitive lump points to an abscess. Feel for thickening of the skin, a consequence of rubbing. Then tug on the hairs in and around the area. If they pull out easily and in a clump, the skin disorder, not secondary scratching, is causing spontaneous hair loss. Note whether the loose hairs slip cleanly out of their follicles or pull patches of skin or scab with them. Remove scabby crusts if the horse will stand for it (sedation might be necessary if the scabs are tight and the horse is sensitive) to see if the underlying flesh is disturbed, and how deeply, and to check whether there's fluid beneath the crust.
The Bad Bug Blues
Many skin problems are caused by insects and parasites. Most insect bites are small, round, soft and usually itchy, with tiny holes in the middle. They crop up in warm and wet seasons, at specific times of day: Mosquitoes and some gnats feast from dusk to dawn; flies feed in the daytime; midges ("no-see-ums") dine at dusk. Insect repellants deter biting pests, but physical protection, including fly masks and sheds and stalls, is more reliable.
In some cases, hereditary allergy to the saliva of "no-see-ums" results in nasty reactions, known as sweet itch and summer itch, that appear on the shoulders, withers, back and tail. Queensland itch affects the hindquarters of horses in the southwestern United States (and the state in Australia from which it takes its name). Oral corticosteroids ease the itch of the moment, while limiting bug exposure can help over the long haul.
If your horse has inflamed, scaly and itchy bumps along his belly or around his eyes and in the center of his forehead, onchocerciasis is the prime suspect. The condition is an allergic response to microscopic worms (Onchocerca) that infest the connective tissues and die in the skin. Corticosteroids can stop the itching, and you'll need to get your horse on a two-phase deworming program with ivermectin-one dose to zap the existing worms, another in three to 12 months to finish off those that were developing at the time of diagnosis.
Horn flies cause ventral midline dermatitis, a condition characterized by spontaneous balding, rawness, crusting and skin thickening. To soothe the condition, gently remove the scabs and wash the area with mild soap; then treat the lesions with an antibiotic and corticosteroid ointment twice a day for several days. To prevent renewed irritation, coat the midline with petroleum jelly and use fly repellant to deter the horn flies.
If your horse is contorting himself to scratch his mane or tail, and you notice droplets of wet or dried serum near the roots of the mane and tail hairs, ticks are probably biting him. Louse powder will kill the parasites, and vegetable or mineral oil applied to the base of the mane and tail discourages tick attachment.
Bites from lice, which crop up in winter, cause extreme itchiness, a heavy, waxy dandruff and bald patches. If your horse's mane and tail are balding slightly and shedding dry dandruff, mites are likely to blame. Dust or wash the infected horse, plus everything and everyone he touches, with an insecticidal preparation.
The horsefly-sized insects known as warbles lay eggs on their hosts' legs. Once the warble larvae hatch, they burrow into the skin and migrate through the tissues. When they reach a likely spot-usually the horse's back-they form anthill shaped lumps on the skin surface. Each larva's apartment has a tiny breathing hole that oozes pink fluid. Getting rid of warbles is tricky, since crushing one in the skin can set off a possibly fatal allergic reaction. A veterinarian must carefully widen the breathing holes and then draw the larvae out. Ivermectin kills warble larvae before they can migrate.
If you're still not sure about your horse's skin abnormality, take time to consider when you first noticed it and how it has changed since. Make a written record of all pertinent details:
- When did the problem start and how quickly has it progressed? Skin conditions that grow fast and worsen continually, especially if they cause open lesions or crustiness, are more likely to be serious.
- What were the characteristics of the condition at each stage, and what effects have attempted treatments had?
- Has the problem occurred before? Does it come and go with certain seasons or under particular conditions?
- Was your horse exposed to chemicals, detergents, unusual foliage or any other potential irritant?
- Has there been a recent change in his routine, environment, grooming equipment/supplies, feed or medication?
- Do herdmates have the same problem? Are his relatives similarly affected?
If fever, appetite loss, fatigue, depression, general edema, diarrhea, or elevated pulse and respiration accompany any skin condition, call your veterinarian at once.
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This article originally appeared in the August 1998 issue of EQUUS magazine.