Ahhh, spring. Another winter is past, and the first warm, balmy breezes promise a long season ahead to enjoy time with our horses.
Of course, spring also brings its own horse-care challenges. You’ve already administered vaccines and taken care of deworming. Mud will rule your world until the rainy season is over, and—look—your horse is already stomping at flies.
And then you notice some odd-looking bumps on your horse’s neck and shoulders. Is this some sort of allergy? Fly bites? Maybe something worse?
Horses can develop allergies, infections and other skin conditions at any time of year, but some are more common during the warm, wet spring weather. “The more temperate the climate, the more changes you’ll have in the seasons, and the more noticeable the seasonal differences in skin problems,” says Stephen D. White, DVM, DACVD, of the University of California–Davis.
Here are four equine skin problems that are common in the springtime months. By watching out for them, and taking action at the first signs of trouble, chances are good that they will be cured without delay and your horse will be healthy and comfortable all season long.
Allergies to insect bites
Hypersensitivity to insect saliva is among the most prevalent of equine allergies. A severe form, called sweet itch or summer itch, is a reaction to the bites of tiny midges (Culicoides spp.). But horses can also become sensitive to the bites of other insects, including mosquitoes, deerflies, stable flies or black flies.
“The first thing we generally think of, in terms of springtime problems, are ectoparasites, which include winged insects,” says White. “There are a number of insects that torment horses but one of the most troublesome is this group of gnats or no-see-ums.”
• Signs: Extreme itchiness is the most prominent sign, and a horse’s constant rubbing of the affected areas will produce hairless patches with inflamed, scabby skin. The location of these lesions on the horse’s body depends on the particular species that are biting him.
“Here in Florida, for example, there are at least 23 species of Culicoides,” says Rosanna Marsella, DVM, DACVD, of the University of Florida in Gainesville. “Many like to feed on the neck and tail area, so the itchy horse rubs his neck and tail against fences and trees. Other types feed on the chest or ventral part of the horse and cause ventral midline dermatitis---a crusty itchy lesion underneath the belly. This is why, depending on the kind of Culicoides in your region, you may see a variety of clinical presentations and distribution of lesions on horses, but they are all itchy.”
• Risk factors: Practically any horse can develop hypersensitivity to insect bites, but certain breeds---including Icelandic Horses, Welsh Ponies and Shires---tend to be more susceptible.
• Treatment and management: Caring for a horse with sweet itch requires a two-pronged approach: to treat his skin, and also to keep the biting insects away from him:
• Use topical treatments to soothe the itch. “Things we recommend to decrease the hypersensitivity and itching include topical steroids rather than systemic steroids,” says Marsella. “In addition to increasing the risk of laminitis, long-term use of systemic steroids can hinder the immune system. So we often use topical sprays that can be applied to selected areas of the body to make the horse more comfortable.” Topical steroids may also be helpful. Your veterinarian can help you choose appropriate treatments for your horse.
• Apply appropriate repellents. Read labels on these products carefully. Some are insecticidal, which means they kill the fly only after it has bitten the horse. Others are repellents---they discourage the flies from landing on the horse at all. If your horse is allergic to the bites, the insecticides won’t help; you need the repellent. You’ll also need to keep close tabs on your horse and reapply the products as they wear off.
• Keep horses indoors when insects are most active. “Mosquitoes and Culicoides tend to come out at dusk and early in the morning,” says White. Keeping horses in their stalls during those periods will help to protect them from those insects.
“If horses are kept in stalls, you need screens or netting with smaller squares than ordinary screens; the Culicoides are so tiny they can crawl through most screens,” White adds. Look for netting or screens labeled for use against “no-see-ums.”
“Having fans in the barn can also help, since these tiny insects are weak fliers,” White says. “Horses will learn to turn toward the fan, and the moving air can blow the gnats away.”
• Outfit your horse in fly-proof garments. In addition to the standard fly sheet, look for accessories---ear nets, belly bands, tail covers, etc.---that protect the parts of your horse the midge species in your area tend to attack. Look for products with fine-mesh netting; many are designed specifically for horses prone to sweet itch.
• Limit insect breeding areas. Culicoides lay their eggs in still water or moist soils enriched with organic matter, such as marshes and the banks of ponds and streams. If your pastures lie near wetland habitats, your ability to control the populations may be limited, but you can take steps to close down any breeding areas on your farm. If you consistently have muddy areas or standing puddles contaminated by manure, for example, look for ways to improve the drainage so water doesn’t accumulate.
Note: Hyposensitization (immunotherapy) treatments used to reduce or eliminate pollen allergies are not effective against allergies to insect bites.
“At this point, studies using allergy vaccines for insects have failed to show efficacy,” says Marsella. “Since horses cannot be ‘desensitized’ to insects the same way we do with pollen, your best defense is keeping these little flies away from the horses.”
Just like people, horses often develop pollen allergies in the warm spring weather when various plants start to bloom. “Environmental allergies due to pollen is a condition that is often under-recognized by horse owners and veterinarians,” says White. A horse who develops signs of allergy at the same time each year may be reacting to something seasonal in his environment.
The timing of these allergies can vary, depending on the growing seasons of trees and other plants in your region. Although these allergies may begin in spring, depending on the particular plants a horse is sensitive to, they can also appear throughout the summer or fall. “Here in northern California there are some plants that start pollinating by mid-January and go through April,” says White. “Trees tend to pollinate first in the spring, and grasses a bit later [maybe June or July] and many of the weeds [such as ragweed] pollinate in August. Horses can have a hypersensitivity reaction to any of those.”
• Signs: Allergies to pollen and other airborne environmental contaminants, such as molds or dusts, can cause respiratory signs, commonly called “heaves,” as well as skin reactions. Most horses exhibit one type of signs or the other, but not both.
On the skin, pollen allergies cause atopic dermatitis, which can include hives (soft, raised, flat-topped swellings in the skin, also called urticaria) and/or itching (pruritus). It’s possible for a horse to have hives without itching, or itching without hives, or both together. “Atopic dermatitis is like eczema in people, with similar distribution on the body---primarily on the horse’s face, armpit, groin or wherever there are folds of skin,” says Marsella.
• Risk factors: Horses who are already sensitized to one type of pollen might be more likely to develop new allergies to other allergens. Heaves typically develops in horses older than 9 years.
• Treatment and management: A horse with constant hives and/or itching can be treated with anti-inflammatory drugs, but these have limitations. “Corticosteroids help a lot but carry their own problems and side effects [such as an increased risk of laminitis],” says White. “You don’t want to use these very often.” Antihistamines may also help some horses.
For itching that affects only small areas of the skin, a topical ointment designed to suppress the immune response, such as tacrolimus (brand name Protopic), may be a good option. This may help to stop the horse from rubbing specific areas, such as the ears, legs or face.
It’s also important to determine which specific plants are causing the horse’s reaction. “In some cases your veterinarian may suggest skin tests or a serum test to try to determine what allergies the horse has,” White says.
Skin tests involve shaving a portion of the horse’s coat and injecting a variety of different potential allergens into a grid pattern of dots in the very top layer of skin. Then the dots are examined over time (usually 20 minutes to 24 hours) to see which ones produced allergic reactions. For the serum test, your veterinarian draws a blood sample and sends the serum off to a laboratory, where it will be tested for antibodies to allergens. Very high levels of any one type may indicate an allergy.
With the information gained from these tests, your veterinarian can formulate a course of treatment called hyposensitization---a series of either injections or oral drops designed to decrease a horse’s sensitivity to the allergens. The exact schedule may vary, but the sequence will begin with more frequent injections or oral administrations of very dilute formulas that contain the allergen; over time, both the concentrations and the time between the administrations are increased. A full course of hyposensitization takes at least six months up to a full year. “The success rate for these treatments is probably about 70 percent,” White says. Most horses need life-long treatment.
Minimizing a horse’s exposure to a plant pollen that causes allergies may not be possible. You can mow down offending weeds on your own property, for example, but pollens travel on the wind. If a horse is miserable with pollen allergies despite treatments, the best solution may be to move him to a climate where the offending plant does not grow.
Pastern dermatitis (“scratches”)
Snowmelt plus spring rain equals wet turnouts each spring in many parts of the country, and for many horses that means the proliferation of crusty, scabby skin between the heels and the fetlocks. “Scratches” is what many horsepeople call pastern dermatitis, which is itself a general term that simply refers to inflammation of the skin on the pasterns. “Any crusty lesion on the lower legs is usually called scratches,” says Marsella.
Pastern dermatitis often develops when bacteria or fungi invade tiny cracks in the skin caused by repeated cycles of wetting and drying. But there are many other potential causes as well, including mange, sweet itch, other allergies, ringworm, photosensitivity and vasculitis (inflammation of the blood vessels). “Depending on how tall the grass is in the pasture, the horse may also have rainrot infection on the lower legs,” says Marsella.
Whatever the primary cause, the inflamed, damaged skin often opens the door to bacterial infections. “They start the problem with the itching and inflammation, which leads to a secondary bacterial infection,” says Marsella. “The horse has insect bites and is allergic, then gets a little bit of a staph infection, and this makes it even worse.”
• Signs: The exact appearance of dermatitis on the lower legs may vary, depending on the specific cause. Generally, you’ll see tight scabs and crusting (irritated, flaking skin), possibly with oozing serum or pus.
• Risk factors: Any horse who spends time on wet footing may develop pastern dermatitis, but those with heavy feathering are at higher risk, because the long hair holds moisture against the skin. Draft breeds in particular are prone to several conditions that affect the skin of the pastern.
• Treatment and management: In a milder case---when the horse does not seem to be in any discomfort---you can treat the condition without veterinary help. First, move the horse to a dry area and hose off any mud or debris from his lower legs. You may also want to trim away any longer hair. Then cleanse the affected skin with an antiseptic wash.
“These infections can be treated with chlorhexidine or benzoyl peroxide to kill the bacteria that cause the crusting,” Marsella says. Avoid products that contain more than 2 percent of the active ingredients; these may further irritate the skin. (Also, avoid using “home remedies.” Many will cause further injury to the skin, and even the ones that do work are no better than the commercial products.)
After cleansing, allow the skin to dry thoroughly, then apply an antibiotic ointment. In addition to helping to kill bacteria, the thicker preparation can form a protective barrier against further infection. Repeat the treatments every two to three days. Most cases will heal within two weeks.
Call your veterinarian if pastern dermatitis fails to heal or continues to get worse despite treatment; also call your veterinarian at the outset if you see any swelling or the horse seems to be showing signs of pain or itching. Your veterinarian will want to test the lesions to identify the cause,and may prescribe a better-targeted or more aggressive treatment. Some horses just seem to be more prone to scratches than others, but if one of yours develops the condition repeatedly while others do not, your veterinarian may want to look for underlying conditions, such as Cushing’s disease, that may affect the horse’s immune function.
Preventing scratches means keeping your horse’s footing as dry as possible---an admittedly difficult task in wet seasons. Fastidiously cleaning stalls---to remove urine soaked bedding and allow wet spots to dry before putting new bedding down---is an important start. Also look for ways to improve drainage to avoid standing water in pastures, and consider laying gravel or heavy-duty mats in high-traffic areas such as around feeders or at the gate.
You’ll also want to minimize other environmental factors that might irritate the skin of a horse’s pasterns---such as coarse arena footing or bell boots that are too tight. Some chemically treated bedding may irritate a horse’s skin. When clipping or grooming your horse, take care not to nick or scratch the skin.
Spring rains and constantly wet pastures from snow thaw mean horses who live outside may be vulnerable to a skin infection called rainrot or rain scald. “This bacterial infection is caused by a pathogen called Dermatophilus congolensis, which is an anaerobic bacterium,” says Marsella. “This condition may also be complicated by secondary staph infections.”
Although rainrot was long believed to be a sign of neglect, the infection can develop even in horses who receive scrupulous grooming and care. We now know that the dirt on the coat isn’t the source of the rainrot; rather it’s persistent moisture, plus a break in the skin, that allow the dormant bacteria on the skin to activate and multiply.
Rainrot often develops in the fall and winter, when heavier coats trap moisture against the skin. However, says Marsella, “in the springtime, conditions may be ideal for rainrot because flies are out and the horses have fly bites and are itchy. They are scratching and scraping against fences, etc., and creating injuries to the skin. Then there’s more rain and the skin is compromised and softened by the moisture and scrapes, so it’s easier for bacteria to establish an infection.”
Another important point: The bacteria that cause rainrot can be passed via contact directly from horse to horse, and to people as well. “If the horse has rainrot, and you ride bareback in shorts because it’s a hot day, you can get this skin disease,” says Marsella. “This doesn’t mean that everyone who touches the scabs will get it. There must be a combination of exposure and a weak or compromised immune system.”
• Signs: Rainrot produces distinc-tive gray/white scabs with tufts of matted hair that rise above the sur-face of the coat. Yellow-green pus may be visible underneath. Over time, the scabs will slough away, leaving patches of hair-less skin.
The crusts may appear anywhere on the horse that remains consistently wet. “If they are out in the rain we see the crusts along the top part of the horse,” says White. “If horses are standing in mud or wet conditions we see the problem on the distal extremities [lower legs].”
• Risk factors: Any horse who lives in persistently wet conditions---from rainfall or a wet pasture---may develop rainrot. But factors such as malnutrition, advanced age, illnesses such as Cushing’s disease and stress can compromise a horse’s immune function and increase the risk of developing the infection. “The ones that get rainrot are usually the young, old or stressed individuals,” says Marsella.
• Treatment and management: The first priority for treating a horse with rainrot is to dry out his skin and coat. This may mean moving him into a dry stall and, if the weather permits, clipping away a winter coat so air can reach the skin.
Mild cases generally respond well to over-the-counter products---shampoos as well as topical rinses and wipes---labeled for use against rainrot. “A common misconception is that iodine is a good treatment for rainrot, but it’s not the best choice,” says Marsella. “We have much better products now, with very effective ingredients. The best is benzoyl peroxide, the same ingredient in human products for acne. It’s a very good antimicrobial agent and also opens the hair follicles, helping the scabs come off. Another product that is good for treating rainrot is chlorhexidine. However, the chlorhexidine doesn’t work as well as benzoyl peroxide for dislodging the crusts and scabs.”
Any scabs that are loose enough to fall away can be gently removed, but it is painful to the horse to tug at any tufts that are still tightly attached. “You should not pull the scabs off, partly because it’s painful, and also because if the skin is not ready for the scab to come loose it leaves an open area and can lead to scarring. The hair may not grow back the same,” says Marsella. “When the scabs are ready to come off, they will come off on their own.”
Call your veterinarian if a case of rainrot does not begin to clear up after a week of treatment. She will check to make sure the infection is actually rainrot rather than another similar-looking condition and may prescribe stronger medications, possibly including an oral antibiotic, to help address a more serious case.
Preventive measures for rainrot include keeping horses dry. For those who live exclusively on pasture, this means providing a deep, dry run-in shed and monitoring herd dynamics to make sure low-ranking members aren’t being constantly kicked out into the rain. Waterproof rainsheets may be a good idea for horses who are particularly susceptible to the infection---but you’ll need to check underneath each day to make sure a sheet is not trapping moisture against the horse’s skin.
Regular grooming is also a good idea, not just to clean mud off your horse’s coat but to monitor the health of the skin and catch developing infections early. You’ll want to treat even minor wounds with a mild disinfectant labeled for that purpose, and use fly spray regularly to minimize itchy bites that make the horse scratch.
Even as you enjoy the first glorious days of spring, you may want to make a few adjustments to your horsekeeping routine. “The best management practices to avoid skin problems in the spring and moving into summer are to keep horses dry---out of the rain, mud and swampy areas,” Marsella says. In short, take a few simple steps now to protect your horse’s skin so that you’ll be able to enjoy more carefree time in the saddle this summer.
This article was originally published in EQUUS 486, March 2018
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