Dealing With Rain Rot

It’s that time of year in the Pacific Northwest when “rain rot” makes its annual appearance.

Rain rot is an interesting infection. It is one of the few horse diseases that bothers you more than your horse. The only painful part of the disease for your horse is when you remove the scabs. The actual infection does not cause your horse any pain or irritation — not even any itchiness.

This disease is also known by a few other names, including:

  • dew poisoning (when it’s on the legs)
  • rain scald
  • streptithricosis
  • mud fever

Throughout this article, the terms are used interchangeably.

What does rain rot look like?

The hair looks rather dull and lifeless where the rain rot is. If you were to pull on those tufts of hair, they would come out very easily, and under them you would find pink skin, probably oozing a little bit.

It is important to get these scabs off, as that allows air to get to the skin underneath them, which helps heal the infection. If the infection gets severe, the horse will start to lose hair. This is extremely unsightly, yet it does not cause the horse any discomfort.

Once the scabs have been removed and the skin starts to heal, it will dry up and be grey in color.

What causes rain rot?

Dew poisoning is caused by a nasty little organism called dermatophilus congolensis. Thankfully, like a number of nasty little organisms that invade our horses, D. congolensis is pretty easy to keep at bay. Before you can successfully keep it at bay, though, you need to know a little bit more about it.

D. congolensis is a facultative anaerobe. This means that it uses oxygen to produce energy, when it’s available. But it is also able to switch to fermentation, when necessary, and is perfectly at home in an oxygen-deprived environment.

How is rain rot transmitted?

Rain scald, or rain rot, is transmitted a number of ways. It can be transmitted directly between horses, or it can be carried on items that are used on an infected horse then on another horse. The most usual culprits for spreading rain scald (which is very contagious) are grooming tools. Prevention of this disease is just one reason it is a good idea to have a set of grooming tools for each horse.

Another common culprit is shared saddle blankets or pads. Or pretty much anything else that touches a horse’s skin and is shared between horses. One place that many owners wouldn’t think about as spreading rain scald is any place a horse regularly itches himself where another horse might also itch. So if you can’t determine a source of infection, look to your pastures and/or stalls, and see if there is a place (tree, post, etc) where most of the horses are scratching themselves.

It’s important to keep in mind that horses can be carriers of this disease without showing symptoms…so a seemingly uninfected horse can still transmit it to another horse if he’s simply carrying rain scald and not displaying symptoms. Also important to note is that horses can re-infect themselves if the grooming tools and tack are not treated after every contact with the infected horse. Also treat any scratching areas such as trees or posts.

How does rain rot get started?

Contrary to popular belief, a horse in any climate and conditions can acquire rain rot. Like the name implies, it is most often found in warm, humid climates or rainy climates like the Pacific Northwest.

D. congolensis needs a moist environment to thrive and reproduce. This disease can be more common during the winter months due to the long hair coats that horses develop. The winter hair coat is great at trapping heat and sweat near the body, creating the perfect environment for D. congolensis.

Once your horse has picked up the organism, he doesn’t necessarily become infected. In order to become infected, his skin must be compromised to allow the organism entrance. Usually this happens through a bug bite or a scratch or scrape.

How can I prevent streptothricosis?

Streptothricosis is most easily prevented by good horse-keeping practices. Horses that are generally kept dry and clean will usually not develop streptothricosis. However, if you have recurring issues with rain rot, it is wise to look into the underlying causes. The most common cause is a lack of proper nutrition.

How do I treat Rain Rot?

Dew poisoning is best treated by first giving the horse a bath with soap to loosen and remove the scabs. Some people choose to use a medicated shampoo, while others simply use any regular shampoo. Let the soap sit on the horse for a few minutes to loosen the scabs. After a bath, the area will need to be treated with something to get rid of the organism. You can then use a number of things, including antiseptic ointment or other remedies that are available at most feed and tack stores.

Here at NWNHC we have successfully used the following products to treat and prevent the spread of rain rot.

Tea Tree Oil—Mix concentrated Tea Tree Oil with water in a spray bottle and apply daily until cleared. Dilute one part Tea Tree Oil with nine parts of water (1:9).

Dynamite Excel—Detoxify and start rebuilding the horse’s immune system. Top dress COB with 1 teaspoon of Excel for 30 days. Then rebuild horse’s immune system with the Dynamite Equine Foundation Program including PGR feed, Dynamite vitamins and Dyna-Pro prebiotic.

Products are available online or at the NWNHC Store, 32925 SE 46th St., Bldg A, Fall City, Wash.

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