Page 77 - Speedhorse December 2019

paddocks, but frequent excessive bathing leaves the legs wet and this is hard on their skin.” It’s just like human hands being continually wet and dry, wet and dry. The skin tends to chap.
“Even though the owners want their horses clean and shiny, this is not the best for the skin,” he says. “We create a situation where we set the horse up for inability to adapt; the skin never knows whether it will be wet or dry.
“A complicating factor in scratches, because there’s very little agreement on the cause, is that people tend to use a variety of pharmaceutical and chemical treatments. Since this is a frustrating disease and doesn’t go away quickly, horse
owners may get overzealous with the number of treatments they apply—using various soaps, salves, and sometimes caustic medications. These may deter healing by creating chemical damage to the surrounding skin, in addition to the initial lesions. I’ve seen cases where a relatively minor infection got out of hand, and I suspect it had something to do with an overzealous owner using multiple chemical treatments simultaneously. The horse owners or trainers are trying to do what they can and may get carried away because there are many people giving different advice and opinions on treatments.
“Here at our clinic we have a
pharmacy technician who does a lot of our compounding,” says Evans. “Our scratches ointment is a mixture of zinc ointment, a
little furacin, penicillin, and a little bit of corticosteroid to help decrease the swelling and reactivity of the skin. We use this cream fairly liberally at first, to soften the crusts so we can take them off and get them out of the way. Once we get the wound cleaned up so there are no crusts or debris, we use it more sparingly to allow dry air and sunlight to get to the area. I think sunlight and fresh air can help it heal. This not only helps scratches, but also some of the other skin lesions like ringworm.
“Many skin problems will readily heal— and we call those self-limiting—if the horse
is out in the sunlight, whereas if the horse is blanketed all the time and kept in a barn where it’s damp and there’s ammonia in the air, this makes things worse.”
Sometimes other infections, like bacterial folliculitis, can look similar to scratches but is
not as common. “It is similar to what is seen in dogs and humans, with bacterial infections of the hair follicles and secretory glands of the skin,”
he says. “There are some types of bacteria that are normally found on the horse’s skin, such as various staphylococcus and streptococcus species. If there is trauma to the skin, or if the horse has
a lot of fly bites, the bacteria have access and can invade the follicles. It’s like acne in that it can appear almost anywhere on the horse. It tends to look a little like scratches at first, but has a greater distribution. Scratches (pastern dermatitis) is almost always limited to the back of the pastern
Rain Scald is a wet-weather skin problem that typically shows on the back, shoulders and rump, looking similar to rain dripping down the horse, and likely comes from carrier horses through direct contact. Wet conditions can trigger infection if there is a break in the skin.
initially, whereas these other infections may start anywhere on the body or face.
“There are usually multiple firm nodules. Sometimes there is crusting. There may or may
not be any hair loss. The lesions usually are not itchy, but the client is generally worried about the spreading nodules. For diagnosis, we take a skin scraping or skin biopsy to view under a microscope. We usually identify a lot of white blood cells and sometimes we can see active bacteria.
“Most of the time when I arrive at this diagnosis, the client has been treating it as scratches (and maybe didn’t involve the veterinarian) and has become frustrated. When I look at it, I can see that it’s not typical scratches and do a biopsy. Then the pathologist finds a staph infection. Those require a different course of treatment,” Evans explains.
RAIN ROT (RAIN SCALD)
“We don’t commonly see this in a dry climate, but rain scald is probably the second most common wet-weather skin problem in horses,” says Evans. “In my practice, we see it mainly in winter when horses have snow on their backs and it melts and runs down their back, similar to a horse that’s standing out in the rain a lot.
“The causative organism is Dermatophilus congolensis, which is a flagellated anaerobic bacterium. It’s probably a prehistoric bacterium, compared with some of the others such as staph and strep. The pathogen that causes rain scald has more ancient DNA.
“There are probably carrier horses, and if conditions are right they can spread it to other horses through direct contact. Rain or wet conditions may trigger active infections if there’s
a break in the skin. Horses with rain scald have
a typical crusting hair loss, generally on the topline and down the buttocks and neck—but predominantly over the back, shoulders and rump. Rain scald tends to have a recognizable clinical appearance; the lesions almost look like water beading off the horse, like a drip pattern. The crusts generally correspond with that pattern.
“We can examine samples of the crusts under a microscope and see the flagellated bacteria. They have what’s called a railroad track pattern. These skin scrapings are diagnostic and we don’t have to send them to a pathology lab; we can usually recognize them ourselves,” Evans says.
Treatment is topical. “We like to keep these horses dry,” he explains. “We first wash them really well with chlorhexadine soap to remove the crusts and then apply a chlorhexadine ointment to the affected areas. Generally, the lesions respond favorably if we can then keep the horse dry. If the horse lives outside and we’re having constant rain, I encourage the client
to keep that horse inside. If we’ve just come through a rainy period and the client recognizes that the horse has rain scald and we’ve treated it, and we now have nice weather, I like to see those horses out in the sun, in dry conditions.”
Rain scald can be a cosmetic issue because a large area of the horse may be affected, with hair loss. “Clients wonder if the horse is contagious, but if you are actively treating the horse and keeping it dry, this condition is not any more contagious than the horse was prior to getting it,” he says. “We don’t know which horses are carriers; we generally just treat the affected individuals.
“Rain scald is generally not as frustrating as scratches, because scratches tends to recur over and over again, if conditions are right. Rain scald seems to be more of an intermittent problem, depending on the weather.”
Rain scald lesions can be painful, and the horse may not be able to wear a saddle until these areas heal. “In some cases we have to use anti-inflammatory drugs, such as non-steroidal drugs like phenylbutazone to manage acute pain. On occasion, in horses that seem to have an auto-immune component, I use low dose steroids for 7 to 10 days to get the pain and swelling under control. Most of the cases I see, however, are not very painful—particularly if we get the crusts off. The chlorhexadine cream acts as a soothing salve,” Evans says.
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EQUINE HEALTH