The gleam and shine in your horse’s coat reflects his inner health, and puts a sparkle in your proud eye. Invariably, there will be nicks and scrapes to mar that perfection, but what about the times when portions of your horse’s hair are missing? Hair loss in horses, also known as alopecia, can be a frustrating management concern simply because the reasons for its occurrence are so many and so varied.
Tracking down the reason for skin disorders often becomes an exercise in sleuthing. One important element to consider is whether or not your horse is itching and rubbing out the hair, or if the hair is simply missing because of a disease or immune process that attacks the skin. Let’s look at some of the more common syndromes that cause bald spots on your horse.
Itchy and Missing Hair
Itching, or pruritus, creates a self-inflicted hair loss. Not only should you observe your horse’s general behavior to see if he is scratching himself, but you can scrutinize the skin for features that hint at an itchy condition. Broken hairs cast a high suspicion the horse is scratching the hair away. Reddened skin or tiny scabs are not specific to itching, but might be part of the rubbing process.
One of the most common causes of pruritus is an allergic dermatitis caused by hypersensitivity to biting gnats (Culicoides), popularly known as biting midges or “no-see-ums.” The gnats create a skin problem in the horse known as Queensland itch or summer itch, seasonally associated with periods of high insect activity. The surrounding environment has a lot to do with the presence of these gnats in your horse’s world. Culicoides gnats prefer breeding in slow or still water such as that found in ponds, small creeks, or springs.
These pests tend to feed on the sensitive skin of the belly, inner thighs, poll, mane, withers, and tailhead. Intense irritation created by these insects stimulates a horse to frantically scratch on anything in sight—a post, the side of the barn, feeders, trees and bushes, or the ground. An initial hint that something is truly amiss will be the glaring sight of the worsening “rat tail” appearance of your horse’s tail. A prized, flowing tail might be rubbed out in just a few days as the horse vigorously responds to the miserable itch. Often, the mane is also mutilated and bald. Usually the rubbing starts out lightly, then progresses as the allergic response progresses. As years go by, susceptible horses tend to become more sensitized to the bites; the condition worsens with more aggressive self-excoriation (abrading away) of the skin and resultant larger areas of hair loss.
Management of this condition is possible. Affected horses should be stalled, particularly during dawn and dusk when the gnats are most actively feeding. Screens on the stalls are helpful, but the mesh has to be small enough to prevent passage of the gnats. Insecticide spray-misters also help in reducing the numbers of gnats. Fly/mosquito sheets on the horses help to some degree, but remember these bugs prefer the abdomen and thigh areas that are not covered well by a fly sheet. Insect sprays containing permethrin are helpful when applied regularly to susceptible areas of the horse. Keep in mind that in many cases the gnat might feed on the belly, but the systemic allergic response creates itching specifically over the topline of the horse.
Treatment for the condition relies on excellent management and insect control strategies, but some horses might require systemic administration of corticosteroids and/or hydroxyzine to control the allergic response. In extreme cases, a severely affected horse might need to be relocated to a different property away from standing water and gnat breeding grounds.
Another itchy condition that causes hair loss used to be quite prevalent before the advent of ivermectin, and is caused by Onchocerca cervicalis. This parasite enters the horse from a bite by an infected gnat. The Onchocerca larvae migrate to the nuchal ligament along the top of the neck, where they develop into adults. Then they release microfilaria, which are tiny filamentous larvae that infiltrate the horse’s skin. Dead and dying microfilaria cause a mild pruritus and associated hair loss, usually seen along the belly, withers, neck, chest, and on the face. Sometimes you’ll see depigmentation around the muzzle or along the belly also caused by dying microfilaria.
Fortunately, ivermectin has all but eliminated this skin syndrome in horses. This popular deworming medication kills the microfilaria and larvae, but not necessarily adults. The use of ivermectin two or three times a year provides an effective control, and is available over the counter where deworming products are sold.
Horn Fly Dermatitis
The horn fly bites horses to obtain a blood meal, and this is associated with pruritus. Areas of hair loss will appear on the side of the neck or on the underbelly of the affected horse. Good fly control measures are important, while anti-inflammatory corticosteroid ointments control localized irritation and hair loss.
Lice Infestation (Pediculosis)
Lice by themselves do not cause immediate hair loss, but they create an intense amount of pruritus and cause the horse to scratch itself incessantly. With repeated scratching comes hair loss. To identify if your horse has been infested with lice, see if you can see lice marching through the hairs. A magnifying glass is helpful in your visual search—pay particular attention to areas beneath the mane, the shoulders, the back, and the base of the tail. Spread the hair apart and look for dandruff-like particles that move. These would be biting lice moving rapidly away from the light. Sucking lice move more slowly, and you might need to look carefully for their heads embedded in the skin. The good news is that lice are species-specific, and although a nomadic louse might walk upon you looking for a new home, it’ll retreat back to the safety of equine skin as soon as it finds a proper candidate. Lice cannot survive more than one to three weeks off their preferred host.
Treatment of your horse involves bathing with appropriate medicated shampoo products specifically targeted for louse therapy. The biggest problem with this strategy is that louse infestation most commonly occurs in winter or early spring when the horse sports a thick coat; that is a difficult time of year to bathe a horse. Lice cannot reproduce in or survive high body surface temperatures that are prevalent in warmer times of the year. Topical pyrethrin or permethrin products applied two weeks apart are effective against lice, as is ivermectin given in two doses two weeks apart. You should also clean the horse’s tack and grooming equipment with insecticides so he is not re-infected after successful treatment.
Healthy horses with adequately functioning immune systems seem to be affected by lice less often. Situations of overcrowding, poor nutrition, or poor environmental hygiene are stressors that set up conditions for lice to flourish. Ample sunlight and regular grooming are effective tools in minimizing the risk of louse infection.
Mange is not a common condition in horses in the United States, but should be considered in a horse which is very itchy and losing hair. There are several types, named for the type of mange mite that causes them.
Psoroptic mange mites like to inhabit the mane, forelock, base of the tail, or long feathers on the legs of draft-type breeds. Chorioptic mange mites also have a predilection for the long leg hairs. Demodectic mange is unusual in horses and is seen mainly in immuno-compromised individuals. Sarcoptic mange has been altogether eradicated in horses in the United States.
Identifying mange in horses requires examination of skin scrapings under a microscope. The use of ivermectin is recommended in treating mange mites, along with topical application of potent chemicals that should be obtained through your veterinarian.
Missing Hair, No Itching
Alopecia also occurs because the hair simply falls out from inflammation within the skin and/or hair follicles. Some of these problems are of an infectious nature, while others are more innocuous.
Dermatophytosis describes a skin infection caused by fungus. We refer to fungal infections of the skin as “ringworm” since often the lesions are oval or round in appearance. Fungi thrive in dark, damp barns, particularly in autumn and winter months. Once the fungus gets established on the horse’s skin, a long winter hair coat helps maintain the infection. Yet, the time of year should not absolutely define the presence or absence of this as a skin disease. Fungal infections can also become established in warm, humid climates, particularly during fly season, and are highly contagious—easily transmitted between horses by shared tack and equipment.
The incubation period for fungal infections takes anywhere from one to six weeks. An infection might start with a hive-like lesion that then becomes circumscribed in an oval shape. The lesions look scaly and crusty, are accompanied by hair loss, and are commonly seen around the girth and saddle areas, the hindquarters, and along the chest, neck, and face. Sometimes the edges of the lesions have frayed, broken, or distorted hairs just prior to the hair falling out. Usually a ringworm infection is not itchy or painful to the horse, but it can be. Young children are very susceptible to ringworm, so do not let them touch infected horses.
Diagnosis is best made by fungal culture; however, it can take as long as six weeks to arrive at a positive culture. In the meantime, it is best to treat the horse as if it had ringworm. Treatment requires diligent attention to hygiene. All saddle pads, brushes, girths, and cinches must be washed and disinfected, and each horse should have its own designated equipment to reduce the chances of transfer from horse to horse. Remove contaminated bedding from stalls, and disinfect stalls and equipment with bleach, chlorhexidine, or benzalkonium chloride. Isolate infected horses from others.
Daily bathing for the first week, then bathing once or twice a week is necessary to control the infection. Weekly baths should be administered until all lesions have been gone for at least two weeks. The best disinfectants include tamed iodine shampoos, chlorhexidine shampoos, dilute bleach (0.5% solution) rinses, 5% lime sulfur solutions, and a fungal orchard spray (Captan) as an effective rinse. During bathing, work the medicated shampoo into the skin and allow it to remain for at least 15 minutes before rinsing.
Topical salves and ointments can be applied to small lesions. Useful products include miconazole, clotrimazole, and thiabendazole. In extreme cases that occur in immuno-suppressed or very young horses, systemic antifungal medication might be warranted to help the horse’s immune system eliminate the disease. In most cases, ringworm is self-limiting once the horse’s immune system has had a chance to recognize and process the infection. With the help of good hygiene, exposure to sunlight, and frequent antiseptic baths, most horses clear the infection within about six weeks.
A common cause of hair loss on the lower legs is a result of poor hygiene in the stabling or pasture area. Urine or manure scald on the legs will cause hair to fall out from chronic skin inflammation, usually accompanied by crusting and scabs in the areas of patchy hair loss. The environment should be cleansed of caustic irritants like urine, manure, and excrement-soaked straw or shavings. Daily cleansing of the lower legs will clear up most of these without too much trouble. In some cases, systemic antibiotics might be necessary. If you cannot point to damp or dirty environmental conditions, have your veterinarian check your horse for the presence of a bladder or urinary stone that might be causing abnormal urination and scalding of the skin where urine contacts it.
Another cause of hair loss can be attributed to an organism known as Dermatophilus congolensis, which elicits a condition referred to as rain rot, rain scald, or dew poisoning. This organism likes to infect traumatized skin, particularly in the presence of high moisture. Young horses with poorly developed immune systems are at a higher risk of getting rain scald. Skin trauma can happen by abrasions, insect bites, or constant irritation by frequent rain exposure that softens the skin, particularly along the horse’s topline. Often, the initial lesions are seen along the rump, lower limbs, face, muzzle, withers, and in the saddle region. This organism lives in the soil as well as in the scabs of infected horses. Horses might be “infected” with the organism, but show no outward signs of disease. They still remain as carriers to high-risk individuals.
Rain scald lesions are crusty and scaling and the hair pulls away with the crust still attached, revealing an erosion beneath. Initially these might start as raised tufts of hair with crusts. Usually these lesions are painful. Unfortunately, crusting and scaling abnormalities in the skin accompany many types of skin problems, so the best way to diagnose Dermatophilus is to look under a microscope at the cells obtained by a scraping, and to culture the organism from a scraping. A biopsy of the tissue also gives evidence of the cause of the lesions.
In the spring, horses can experience a seasonal alopecia in which large patches of hair shed out before entry of the new hair growth, leaving a bald patch of skin. The area of naked skin appears normal. Given patience, the hair will reappear within about a month.
Considered a benign form of equine skin cancer, a sarcoid also creates hair loss. In many cases, sarcoids appear as flat, hairless lesions with a scaling or rippled appearance to the nude skin. These lesions are neither pruritic nor painful. The most accurate means of diagnosis is to biopsy the lesion.
Sarcoids might be infective from one horse to another if common grooming equipment or tack is used. It is thought that the transfer from horse to horse or soil to horse is by way of a virus. To limit spread to others, practice common sense hygiene strategies in horses with visible sarcoids.
A variety of treatments are available, using methods such as cryosurgery to freeze the sarcoid or direct injection of immune-stimulating compounds (cisplatin or mycobacterium cell wall fraction) into the lesion or by repeated topical application of tissue-toxic products (5-fluorouracil, Xterra) on the lesion.
In certain areas of the country where soil is rich in the mineral selenium, some plants accumulate too much selenium in their leaves, and horses grazing on these plants or horses fed hay that has been grown in selenium-rich soils might suffer from toxicity. Classic signs begin as a thinning of the mane and tail hairs, with eventual hair loss on the mane and tail. In more advanced cases, horizontal cracks will appear in the hooves, with a potential to slough the entire hoof capsule.
Hair, serum, or feed can be analyzed for selenium content. If selenium toxicity is a suspected problem, affected horses should be removed immediately from the offending pasture, or the hay should be substituted with low-selenium hay from a reliable source.
Drug Side Effects
Some medications can also cause patchy hair loss. Check with your veterinarian to see if any drugs your horse is receiving might be behind his alopecia.
An Accurate Diagnosis
The diversity of skin problems in horses is varied, and in many cases visual inspection of the lesions might not accurately diagnose the reason for the problem. The best means of identifying what is wrong with your horse’s skin is to have your veterinarian perform a skin biopsy. A biopsy takes a punch of tissue through all skin layers and gives a definitive diagnosis of the disease process, and in many cases the source of the problem.
In addition, a skin scraping sample can be reviewed under a microscope to determine cell type or identify parasitic organisms, and/or a tissue sample can be submitted to a lab to culture for a fungal or bacterial organism when appropriate. These tests are simple to perform with minimal discomfort to your horse. By pursuing this avenue of investigation, you’ll be able to address the nature of the skin problem and get the hair and the shine back in your horse’s coat as quickly as possible.