Gina G. Tranquillo, VMD, CESMT

Does your horse have a natural shine to the haircoat? This is not only an indication of  good grooming but more importantly, a sign of good health. Your horse’s skin is the largest organ and an indicator of your horse’s internal health and well‐being. During your daily horse assessment, it is important to run your hands and eyes over the entire horse to understand the presence of possible skin diseases that may need prompt veterinary attention. Below are just a few of the many skin conditions you may face.

Pastern Dermatitis (PD)

This condition is caused by Dermatophilus bacteria and affects the back of the pastern and heel bulbs. It is often seen on white marked legs, but not always. Pastern dermatitis can cause the legs to have a “stocked up” appearance and depending on the severity, PD can even cause lameness. This condition is characterized by scabs or crusted lesions. These lesions can remain on the distal part of the limb, or affect more of the limb in severe cases. You may be familiar with other names for PD which include: Mud Scratches, Mud Fever, Dew Poisoning, Cracked Heel, or Greasy Heel. If you suspect PD, it is important to consult your veterinarian. There are many different topical treatments your veterinarian may suggest based on their success. My favorite is one of two topicals made at Hagyard Pharmacy: Dew Poison Ointment or Schmitt Smear. The first stage of treatment is to apply a medicated shampoo to cleanse the skin and soften the scabs so that they can be loosened and removed (debridement). Once the leg is rinsed thoroughly, then apply a topical ointment.  I always recommend applying an ointment without a bandage, as to avoid any friction, irritation, or moisture build up to the area. This approach usually works well in mild to moderate cases. If your horse is suffering from more severe PD, then your veterinarian may even prescribe systemic antibiotics to help alleviate the cellulitis (inflammation of the skin). In addition to topical management, pasture and stable management are very important. Consider keeping the horse stabled until the sun dries the dew from the fields. Keep the pasture trimmed short. If your horse develops severe PD, you may need to create a dry lot where the horse can still be turned out but on dry ground. As you probably concluded, a dry, clean environment is most important for any horse affected by PD and excessive moisture is a major risk factor for development of disease.

Sunburn

Does your horse have a pink nose that is susceptible to the effects of the summer sun? If so, then be sure to think ahead. Prevention is key! One product that works well is a sun shield that attaches to the halter and covers the muzzle. This helps block harmful UV rays and the horse still can graze naturally. In addition, many fly masks have an extended nose portion to help cover the muzzle from the sun. I like to recommend a topical sunscreen with at least SPF 45, which can be applied daily.

Rain Rot (RR)

Rain rot (also called Rain Scald) is a condition caused by Dermatophilus bacteria, which can vary in degrees of pain.  It is very similar to pastern dermitis; however, RR serves to describe other affected areas of the body such as the trunk, neck, and rump (areas that follow the run off pattern of rain on the body). The appearance of disease can vary from small bumps with scabs to open weeping sores. Prime 2 conditions for RR to develop are established when a horse with a dirty susceptible coat is out to pasture during a storm, where the hair becomes very moist and creates an environment for bacteria to invade. If you notice signs of RR, be sure to call your veterinarian. They can examine the horse and likely will recommend bathing the horse in a medicated shampoo. During this process mechanical debridement of the scabs is important. This is accomplished by massaging with the fingertips to loosen the scabs. Once you have removed those scabs be sure to dispose of the hair in the trash so that horses in unaffected areas are not contaminated. Topical medicated treatment is followed by a drying out phase of the affected area. Some cases that are more severe may require systemic antibiotics. By working with your veterinarian you can devise a treatment plan most appropriate for your horse. Remember your horse’s hygiene is important too. Be sure to disinfect all grooming tools, saddle pads, and tack appropriately in‐ between uses. As your horse recovers from RR be sure to shelter them from moist weather. Prevention can be accomplished by regular, thorough grooming, especially for susceptible horses kept outdoors.

Sweet Itch/Culicoides Hypersensitivity

Sweet itch is caused by insects known as Culicoides (biting midges). These insects breed and thrive in areas of standing water. The saliva of the midge upon feeding provokes an itchy dermatitis usually found on the ventrum (belly), tail, chest, and neck of your horse. The skin in one, some, or all of these areas may have scabs, become exudative, and hair loss can be seen. As the name implies, the horse may have bouts of intense itching. It is important to have your horse examined by a veterinarian, followed by medical treatment and stable management. Since midges feed at dawn and dusk, it is wise to keep your horse stabled at these times with a fan or two aimed at all levels of the horse’s body. Other management strategies would include the following: place a screen mesh on the windows of the stall with openings small enough to prevent midges from flying in, stable the horse in a dry pasture (away from breeding grounds of mud and water), provide a fly sheet with mesh small enough to prevent midges from feeding (especially making sure the fly sheet has a portion to cover the belly), control the insect population in your barn and run in shelters, keep stalls and run in shelters free of manure, and place baby oil in a spray bottle and apply to the horse’s mane and tail to create a slick surface and prevent the midges from landing. If horses develop severe disease, your veterinarian may prescribe corticosteroids.

Photosensitivity

This skin ailment is an abnormal reaction of the skin when exposed to light and can be noted as a purplish/red discoloration àswollen painful areasà progressing to exudative, thickened scabs mostly on the pink skin lying perpendicular to the rays of the sun (ie. face, dorsum of fetlocks, and coronary bands). Once a horse has developed photosensitive skin areas it is often painful like sunburn.

Primary photosensitivity y is often caused by excessive amounts of ingestion of photodynamic agents from a number of plant and chemical toxins, or caused by use of specific systemic or topical medications. Once a horse consumes plants or chemicals with these pigments, the pigments circulate to the skin where they are exposed to UV light, fluoresce and cause oxidative injury to the skin cells. Compounds containing these pigments include: Buckwheat, St. John’s wort, perennial ryegrass, phosphorous fertilizer, wood preservatives, tetracyclines and phenothiazine tranquilizers. At times even alfalfa or clover can induce a photosensitivity reaction.

Secondary Photosensitization occurs when a toxin damages the liver. This causes the inability of the liver to excrete phylloerythrin, which is a compound formed by the microbial degradation of chlorophyll in the gut. Normally, phylloerythrin is removed routinely by the liver and excreted in the bile. However, in liver disease, phylloerythrin can accumulate in the blood and subsequently the skin. When the skin is exposed to UV light, phylloerythrin will fluoresce and cause oxidative injury to the tissues of the skin and blood vessels. Some causes of hepatogenous photosensitivity include: fiddleneck, tansy ragwort, tarweed, and common groundsel. If this disease is suspected it is important to contact your veterinarian so he/she can obtain an accurate history and perform a thorough physical examination. In addition, it may be important to test ingested feeds or plants. To protect your horse, shield the areas with wraps, a sunshield muzzle cover, or full body sheet. An application of zinc oxide cream may be helpful. In susceptible horses, avoid feeding trigger foods that may incite the disease process and always protect the pink skin from sunlight. If your horse’s case is severe, your veterinarian can suggest a management protocol aimed at protecting your horse from sunlight and relief of inflammation and pruritus (itching).

Just remember, there are many other types of skin ailments that can affect your horse. Always consult your veterinarian to establish a diagnosis, treatment plan, and scheduled follow up to keep your horse healthy and happy!