Misconceptions about rain rot in horses

Mar 22, 2021

Written by our friends at MannaPro

You might be surprised to learn that rain rot is not a skin condition that occurs only due to neglect or poor care of the horse. Even the most diligent horse owner who provides the best care can have a horse experience rain rot.
If your horse develops crusty scabs that peel off with clumps of hair and leave bare spots on the skin, then they have probably contracted rain rot. This condition is aptly named, as it is caused by rain or moisture on the horse’s coat and is fairly common. It is also sometimes called “rain scald.”

It is most prevalent in regions of the country where there is high humidity, heavy rainfall, and warm temperatures with an abundance of insects to complicate the condition. The culprit that produces the bald skin and unsightly crusty scabs is the bacterium Dermatophilus congolensis.

Test your knowledge of this common condition, and learn your treatment options for rain rot below.

True or False? Rain rot affects only horses that are left out in the rain for excessive periods without a blanket or run-in shed for protection.

Answer: False – While it is true that rain rot is a common condition in horses whose skin is exposed to rain, horses can suffer rain rot when blanketed too.

As a caring horse owner, you may diligently wash your blankets each season and re-proof them to maintain their waterproofing. But if you use the wrong product to re-proof them, you may block the air movement or wicking action the fabric previously exhibited that allowed a horse’s sweat or body warmth to evaporate. This can set your horse up for a rain rot condition beneath his blanket.

Always check with the blanket manufacturer for advice on which products to use to re-proof blankets.
Rain rot can also occur when a horse owner uses a rain sheet or older blanketing product that does not have breathability inherent in its fabric. Horses are notoriously oblivious to the benefits of a run-in shed during wet or snowy weather. The run-in shed may provide a safe haven from punishing heat and shade from the sun’s rays, but the rest of the time a horse may simply ignore the benefit of the run-in shed. Provision of shelter will not automatically prevent your horse from contracting rain rot.

True or False? Rain rot can be resolved by peeling off the scabs that form followed by giving the horse a rigorous grooming.

Answer: False – Rain rot is a bacterial condition, and the skin should be treated to avoid the spread of spores. Healthy horses have a natural skin barrier that will block penetration of the bacterium through the skin; however, this may be mitigated by insect bites, wounds or sores, or excessive moisture on the skin which removes the natural protective oils that would usually form a protective barrier.

Rain rot will invade the skin layers, and small, pus-filled bumps or pustules will develop. These bumps can be felt underneath your hand when you feel the horse’s skin. They are a result of the accumulation of white cells and proteins produced by the horse’s immune system to counteract the rain rot bacteria. As the pustules mature, the skin layer below will die off and leave a clump of dead skin cells stuck to individual hairs. These clumps can easily be pulled off and the skin beneath will be raw and red. If the causative factor, such as humidity, is removed, the hair will grow back in 7–10 days. But since the horse will be itchy during this time, and the skin prone to invasion by insect bites or scrapes/wounds and left unprotected by hair, it is vulnerable to secondary infection—a much more serious condition.

True or False? The best treatment is to apply a disinfecting spray to the horse’s coat.

Answer: True – If you apply a wound and skin care treatment to the underside of the horse’s hairs by gently brushing the hairs backward before dousing the area with the disinfecting spray, then the lesions should quickly heal and the further spread of pustules should be prevented. Apply daily for several days to the affected areas.
True or False? Rain rot is similar to dew poisoning.

Answer: True – The difference between rain rot and dew poisoning is mainly one of location. Dew poisoning is generally located on the pastern of the horse, while rain rot affects the neck, back, and top of the head. Dermatophilus congolensis is the causative agent of both conditions.

True or False? Rain rot can develop into a more serious condition if left untreated.

Answer: True – If the causative agent of rain rot in the horse’s environment is removed, the rain rot scabs will slowly disappear; however, the red, raw, and itchy skin left behind makes the horse prone to secondary infection with Staphylococcal folliculitis, a much more serious skin condition. In extreme cases, your horse may exhibit pain, fever, and loss of appetite. It is important that any secondary infection be immediately treated by a veterinarian.

It is therefore prudent to take good horse care measures and to address the rain rot with a topical application to halt the spread of the bacteria and help prevent further distress to the horse’s skin. You do not need to remove the scabs, as the anti-bacterial spray will loosen the scabs and they will drop off naturally.

True or False? Rain rot is more prevalent in certain parts of the country and under certain weather conditions.

Answer: True – For example, temperatures in the southern United States provide a perfect climate for rain rot to affect the horse’s skin. Diligent management of the horse’s environment due to changes in temperature and weather is essential in the prevention of the condition. It is wise to review your blanket practices and clip long winter coats on horses moved from a cooler climate to a more humid location.

In conclusion, the cornerstone of good horse management is prompt action to resolve any horse health issue. The resolution of equine rain rot is relatively easy and can be quickly eradicated with the proper care.

If you have any additional questions about rain rot, stop by your local Co-op.


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