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How to Treat Rain Rot in Horses
Table of Contents
What is Rain Rot?
Rain rot is a common equine skin disease caused by a bacteria. it is easy to diagnose and common in wet conditions. The condition is more common during winter months when the haircoat is thicker, a typical clinical sign is “paintbrush lesions” or bumps of skin and hair that come off in tufts, leaving a bald spot behind.
This condition is easily treated with over-the-counter medicated shampoos and sprays, and should only require an the attention of an equine veterinarian in more severe cases. Rain rot is contagious, so it is important to understand how it is contracted and spread in order to minimize the impact to a stable of horses.
Rain Rot is a bacterial skin disease
Rain rot refers to a bacterial skin disease affecting horses. It is caused by the bacterium Dermatophilus congrolensis.
Also known as rain scald, it appears on the top side of the horse—where rain would fall, and then run off—such as the upper parts of the head, neck, and back. Rain rot is more commonly found in geographic areas with high temperatures, high humidity, and surprise—lots of rain. For example, this condition is more common in the southern region of the United States during the winter season, as horses grow thicker coats that subsequently lengthen drying times.
Under normal circumstances, the horse’s natural skin barrier can’t be penetrated by these specific bacterial spores. However, trauma, like a scrape or insect bite, or prolonged periods of excess moisture can compromise the skin and allow the bacteria to invade. The bacterial spores produce hyphae, which are threadlike tentacles that spread out from the initial site. This causes an acute inflammatory skin condition. The horse’s immune system responds by deploying white blood cells to the area. As these white blood cells accumulate, they create small bumps on the skin, called pustules. Once the bumps mature, the skin dies off, forming a scabby tuft of hair and dead skin. These are sometimes called “paintbrush lesions”1 and can easily be pulled off, leaving a bare, sometimes raw spot of skin behind.
Diagnosing Rain Rot in your Horse
Rain rot can show up in a spotty pattern that can grow into large, scabby patches eventually causing areas of hair loss. It’s generally easy to visually diagnose rain rot without a veterinary visit. However, if you want to be sure, a diagnosis can be made by examining a skin scraping under a microscope. It’s important to note that lesions can be itchy or painful to the horse. If they are located on the back or withers, they can interfere with riding. In this case, it would be best to wait until the skin is healed before resuming a riding program.
The symptoms of rain rot are commonly mistaken for a fungal disease, such as ringworm. Ringworm is a fungus that can be transmitted from horse to horse, and to people. However, ringworm is spread by fungal spores, not bacterial spores.
What’s the difference between bacterial spores and fungal spores?
Fungal spores are single cells that float through the air to help fungi reproduce asexually. Bacterial spores are not for reproduction. They exist for survival in stressful situations. Bacterial spores protect the bacterial DNA in harsh environments until things change and are once again more hospitable7.
How to Treat Rain Rot
Treatment can vary depending on severity and the owner’s preferences. Rain rot is caused by excessive moisture in the horse’s coat. If this is an isolated event, the horse may be able to heal on their own, provided the wet environment is rectified. However, even with mild cases, it is still best to treat it in order to speed up the healing process for the horse.
Simply bathing the horse with an antimicrobial shampoo and removing scabs can take care of the issue. Use caution when removing scabs—this could be painful for the horse. Additionally, the scabs should not be removed until the skin underneath is healed.
An Equus magazine article recommends softening scabs with mineral oil and letting them work themselves loose. After applying medicated shampoo, the scabs should rub off with gentle pressure. Several sources recommend Theracyn Wound & Skin Care Spray as effective treatment against rain rot. Multiple sources also reference tea-tree oil for its antibacterial and antifungal effects. It’s important to note that mixing the wrong ingredients can make skin problems worse; it’s best to only use one product at a time or discuss treatment combinations with your vet before using different products to treat the same area.
Advanced cases of rain rot affecting deeper layers of skin may require veterinary care, such as an antibiotic injection. When administered early, antibiotic injections can also help prevent hair loss. This might be important for owners of show horses.
When you treat your horse for rain rot, it’s important to clean and disinfect anything your horse has had contact with to avoid re-infection. This includes brushes, blankets, and saddle pads.
How to Prevent your Horse from getting Rain Rot
A common misconception around rain rot is that it only affects neglected horses, or horses stuck in the rain without shelter or a blanket. This is not the case. The right environmental conditions can cause any horse to develop rain rot. That said, there are several ways to prevent rain rot:
Removing dirt and excess hair helps keep the skin and coat healthy. When done regularly, it is also much easier to spot a change, such as a skin condition like rain rot. The sooner problems are caught, the easier and more successful treatment can be. It’s important to note that some horses are simply more susceptible to rain rot and may need more precautions than your average horse.
Consider limiting turnout in rainy or wet conditions. If horses are turned out, provide shelter such as a shed. Outfitting your horse in a waterproof blanket can also help protect them from excess moisture.
Proper blanket maintenance.
Did you know blanket maintenance should include more than just occasional washing and inspecting for wear and tear? I’ve been riding and showing horses for 20 years and just learned that blankets should be re-proofed each season. (To be fair, my blankets never seem to last more than a few seasons, but still! Good to know). If you don’t re-waterproof your blankets annually, rain and moisture can get in. However, use caution: re-proofing blankets incorrectly can block air flow and moisture-wicking properties, creating a moist, wet environment under the blanket5. Nikwax is an expert in waterproofing many different things and has a blog post with recommendations specific to waterproofing horse blankets.
Rain Rot is Contagious!
Did you know rain rot can be spread to other horses? As it is caused by bacteria, sharing grooming equipment could transfer the bacteria to a healthy horse.
It’s best to have a separate set of brushes for each horse to minimize the possibility of spreading disease. If brushes are shared, they should be disinfected between each use. If a horse in the barn is diagnosed with rain rot, the horse should be isolated as not to infect other horses that may share a paddock or pasture.
While rain rot is not the most serious disease that could affect your horse, it can be prevented and should be taken seriously. The sooner it is caught and treated, the better!
Practical Horseman: https://practicalhorsemanmag.com/health-archive/prevent-and-treat-rain-rot
Advanced Biological Marketing: https://www.abm1st.com/spores-vs-non-spores-organisms/