Causes, Symptoms and Management of Rain Rot in Horses

What is Rain Rot in Horses?

Rain rot, rain scald, or mud fever when it affects the legs, are common names for a bacterial infection of the skin called dermatophilosis. Most commonly occurring across the topline of the hindquarters, flanks, and/or legs of affected horses, rain rot is caused by the combination of the bacterium Dermatophilus congolensis, which is readily found on the skin of many mammals, and ongoing wet or damp conditions. Often viewed as an issue of neglect or poor management, the fact is that horses can, and do, develop rain rot even when the best of care is given.

How do Horses Get Rain Rot?

While the presence of the Dermatophilus congolensis bacterium alone is unlikely to be an issue, horses get rain rot when the skin is compromised by prolonged periods of moisture, which can strip away the skins protective oils and cause a drying and cracking cycle, the bacterium can invade the skins layers causing an inflammatory reaction.

The most common cause of rain rot is exposure to wet weather for extended periods of time, without enough “dry time” for the skin to recover. Moisture makes both the bacterium more mobile, and the skin compromised, resulting in perfect conditions for an infection to occur. Because horses are generally not bothered by precipitation, the presence of a shelter is no guarantee that horses will have adequate dry time. Many a horse owner has invested money in a lovely run-in shed only to stand in the window looking through a deluge at soaking wet horses, grazing away unconcerned about the weather! During prolonged periods of wet conditions, dry time may need to be enforced through confinement in a stall for part of each day.

The use of turnout blankets can help keep horses dry, but only if carefully managed. Poor blanket and rug management can actually be a contributory factor for the condition. Horse blankets or turnout rugs that are placed on damp or wet horses can exacerbate the problem, as can rugs that get soaked through and are not replaced with a dry one once the horse has had the chance to thoroughly dry. Blankets placed on muddy horses is also a concern, as mud is both damp and abrasive to the skin. Managing seasonal fluctuations in temperatures, with horses naked during the day but blanketed at night, requires particular diligence to ensure that the horse is clean and dry before their nighttime blanket is put on.

There are geographical contributory factors for rain rot, and horses living in very humid locations, or areas with a lot of precipitation, are particularly susceptible to the condition.

The presence of high numbers of biting insects can also add to the severity and spread of the condition through skin penetration, both on the infected horse and to other horses as well, as it can be quite contagious. People, grooming tools, blankets and saddle pads can spread the active bacterium from horse to horse, particularly when the wet conditions are affecting all the horses in the barn.

Immunocompromised horses, or horses in a poor general state of health, are at greater risk of developing the condition.

What are the Sypmtoms of Rain Rot in Horses?

Rain rot presents in a variety of different ways. The skin may feel mushy or flakey, it may have hard lumps or matted hair due to flaked skin and scabs attached to the hair follicles, there may be areas of loose hair or patchy baldness, it may have scabs and raw areas with or without pus and/or a bloody discharge, or it may present as large, raw patches where most of the hair has fallen out. It will often cycle through all of these presentations as the condition worsens.

While mild cases of rain rot may not be too uncomfortable, more extreme cases, particularly those with raw areas and scabs, can be quite painful for the horse. Care must be taken when grooming these areas, as the skin is often extremely inflamed, with open cracks and sores.

Most often, diagnosis based on symptoms is simple and straightforward. In the event of a non-traditional presentation, a culture or biopsy performed by a vet can provide a definitive diagnosis.

How do you Treat Rain Rot in Horses?

The first step in treating rain rot is to eliminate, to the extent possible, the damp conditions that have caused the problem. While humidity is not a factor over which one has much control, when horses are living in rainy or wet conditions, particularly with a blanketing routine that is not well managed, a simple change of routine can go a long way towards resolving the problem. Keeping the affected horse clean and dry is a key first step!

Scab removal is the next step in the process. Often the scabs are loose, and will pull away very easily without causing the horse discomfort. The hair will likely pull away with the scab, which is fine. For larger, deeper scabs, or those that are hard and/or firmly attached, caution must be taken. Try softening and loosening the scabs by gently bathing the area, but don’t force the removal as they may be painful and expose raw tissue underneath, which can exacerbate the problem. Continue daily softening and removal as the scabs loosen. This is a marathon, not a sprint!

Bathing the horse with an anti-microbial shampoo, and using one of the many anti-microbial topical products on the market, should become a daily routine until the condition has cleared.

Mitigate biting insects as much as possible. This may include the use of a fly sheet over the area, if it is not too tender, but remember to launder it daily!

All grooming tools, clothes, saddle pads, etc., which are used on a horse suffering from dermatophilosis must be disinfected daily and should not come in contact with other horses until the condition is fully resolved and the equipment has had a final deep clean. Handlers should be diligent about washing their hands with anti-bacterial soap after caring for an infected horse.

For horses with a persistent infection which is not responding to topical management, a course of antibiotics may be prescribed by a veterinarian. It is a good idea to let your vet know when you are dealing with rain rot and keep them apprised of the progress of the treatment.

Rain rot is a condition which is easier to prevent than to treat, but horses can still develop the infection, even with the best of care. Treatment can be simple and straightforward, or it can be a long, drawn-out battle. The keys to a dermatophilosis free barn are avoiding the factors which can cause it, diligent attention to treatment at the first signs of a problem, and dedication to long-term daily care in the event that an infection becomes persistent. If you follow proper treatment protocols, you will have your horses healthy, shiny coat back before you know it!