What is rain rot? Also called “rain scald,” it is a fairly common skin infection that afflicts horses. It's not actually caused by the rain, but by an organism called dermatophilus congolensis. It's an actinomycete, which is a gram-positive anaerobic bacteria which can branch out to grow large colonies with fairly rapid speed.
This bacteria prefers conditions that are warm, damp, and muggy to grow. When there is the combination of high temperatures and high humidity levels outside, then there will be a risk for rain rot to occur. Now here's the good news: this infection is not something that can cause a major injury to the horse. It can, however, be spread to other horses when infected skin contacts your gear, especially saddles, blankets, and leg wraps, when they are shared.
Most cases of rain rot tend to appear in the spring and summer months. In some areas, rain rot is also known to appear in the winter months due to high moisture levels and warm temperatures that may be underneath a blanket that the horse is wearing.
Where Does a Horse Get Rain Rot?
The most common location for rain rot to appear is along the back of the horse, heading toward the tail. Areas of rain rot also commonly appear near the cannon bone and the back of the fetlock. Depending on the severity of the bacterial infection and the weather conditions, horses have been found with rain rot on their ears, muzzle, and even around their eyes.
When a horse has rain rot only on their lower limbs, some may refer to the condition as “dew poisoning.” It is still the same skin issue being treated if this is the case.
What Does Rain Rot on a Horse Look Like?
You can tell if a horse has been inflicted with rain rot because there will be crusty scabs on their skin and small dime-sized matted tufts of hair on their body. The scabs are very easy to scrape off of the horse and this can cause bleeding in severe cases. Most horses have pink skin underneath their scabs with a bit of pus, which begins to heal as soon as the scab is removed.
In the earliest stages of rain rot, you may also feel small lumps on the coat of the horse as you run your hand along the head and back. As it begins to progress, you may see that the horse begins to lose their hair as the scabs begin to form. You may also see more hair than normal coming out as you brush the horse.
Mild cases of rain rot tend to leave areas of skin that look hairless, but smooth and with minimal scabbing. As the infection progresses, scabbing will increase and you may notice open weeping sores on the horse.
The scabs that are created by rain rot on most horses do not seem to provide an itchy sensation like other skin conditions. There does not seem to be pain associated with them either. Removing the scabs, however, can sometimes be painful for the horse, so be gentle with the process and make sure you have plenty of time. You'll want to wear gloves during this process too. The horse will likely be resistant to the process, so take time to calm the horse throughout.
How To Treat Rain Rot Effectively
The one thing that the bacteria which causes rain rot does not like is oxygen. It grows colonies best when there is a lack of overall oxygen available to them, which is why horses with thicker hair tend to have larger infections. For this reason, you will want to trim down or remove the hair that could be keeping the bacteria from being exposed to any oxygen.
The bacteria also thrives underneath the scabs that it causes on the skin of the horse. You will want to gently remove those scabs with light brushing so that the bacteria can be exposed to an oxygenated environment. Follow up the scab removal with a thorough shampoo and rinse of the horse with antibacterial and antimicrobial products.
It is generally not a good idea to use an antimicrobial ointment on rain rot. Ointments tend to retain moisture next to the skin, which gives the bacteria an opportunity to still survive after a treatment series. If your veterinarian recommends using Nolvasan, Phenol, or Betadine to treat the condition, then apply it once per day over the course of 7 days or according to your vet's instructions.
Ultimately the best treatment for a horse that is suffering from rain rot is to keep them in an area that is dry, clean, and well ventilated. You'll need to separate the horse with this infection from the others to prevent it from spreading. If multiple horses have rain rot, each will need to be separate from one another and the rest of the stable to limit cross-contamination. Give the horse protection from biting insects as well, as these have a small chance of spreading the bacteria also.
What If I Have Rain Rot That Won't Go Away?
There are severe cases of rain rot that do not respond well to these home treatment methods. In this circumstance, your veterinarian may recommend using antibiotics to help remove the infection. There are several antibiotics that are known to kill this bacteria, including penicillin, ampicillin, streptomycin, and gentamycin.
Some horses may have their immune systems compromised by the infection, which may require boosting drugs to encourage the animal to begin healing naturally.
The most common reason to have rain rot that doesn't go away, however, is the inability to completely purge it from shared equipment or having two infected horses together in a stable. Be very thorough with your cleaning protocols when rain rot is present – going over contact items 2-3 times may be necessary.
Only your veterinarian should be ordering these drugs for a horse with rain rot and administering them or providing you with specific administration orders. If you've tried to treat rain rot and it isn't working, and you've taken every step possible to limit ongoing contamination, then schedule an appointment with your vet as soon as you can.
Don't Forget About Cleaning Your Equipment
When you are treating one horse for rain rot, you must be proactive in cleaning all of the equipment that you have in the stable. Every item must be disinfected after every use. It is recommended to use a bleach solution ratio of 2 tablespoons per gallon of water, but not all gear will respond well to a bleach mixture. You can also use vinegar in a 2:1 ratio and then allow the gear to air dry before using it again or other antibacterial cleansers that are specially formulated for your items to remove any lingering bacteria that may be on it.
Identifying Rain Rot Over Cushing's Disease
When looking at rain rot, experienced owners may notice a similarity in surface symptoms to Cushing's disease, which is a metabolic disorder that older horses tend to develop – starting around the age of 18. The difference is in the symptoms that the horse experiences.
Older horses that are afflicted with rain rot will not have changes in their attitude and energy. You will not see fat deposits begin to form over the tail head or along the crest of the neck. When a horse has Cushing's disease, it will typically begin seeking out more fluids to drink, have increased urination, and there may even be changes in body conformation that is noticed.
It is not uncommon for a horse with Cushing's disease to develop rain rot because the disease makes it easier for recurrent infections to happen. Rain rot will not, however, cause Cushing's disease to develop. There is a specific prescription medication that is available for the disease if your veterinarian suspects it, but this will not be ordered until diagnostic tests confirm the diagnosis.
Are You Ready to Treat Rain Rot in Horses?
Knowing how to treat rain rot in horses might give you a daily headache for awhile, but the good news is that the prognosis tends to be very good. It is not a debilitating skin condition, does not generally cause itchiness, and some cases of rain rot even resolve on their own. When the condition seems to be getting worse instead of better or you want to proactively treat it, then this guide and the advice of your veterinarian can help your horse look and feel their very best once again.
The best advice to remember is this: because it is a bacteria, you will need to take cleaning precautions in every way. This includes washing your contact clothing immediately, wearing personal protective equipment, and maintaining a daily grooming ritual to encourage the healing process.
If you take your time, apply antibacterial ointments as recommended, administer antibiotics if necessary, and stay on top of things, then you can begin to see improvements in as little as 2-4 days. For horses experiencing hair loss, a complete restoration of their appearance may take 4-12 weeks, with severe cases taking longer.