The above photo shows the results the research team were able to achieve when they applied the Tea Tree Oil solution on one of their test horses.

The above photo shows the results the research team were able to achieve when they applied the Tea Tree Oil solution on one of their test horses.

Writtten by Penny Hawes, and appeared in our Sept./Oct. 2016 Issue

Got Rain Rot? It’s a common scenario – you’re grooming your horse and you notice a couple of scabby bumps along his back or croup. Or perhaps he looks like he’s developing a sore on the back of his pastern, or has greyish “crud” on the front of his hind cannon bones.

Whether you know it by the name rain rot, scratches, crud, mud fever or greasy heel, this skin problem plagues horses, and their owners, any time there is sufficient dampness to give the infection a hold. It’s often more cosmetic than medically serious, but left untreated, horses can be faced with everything from secondary fungal infections to acute lameness. Fortunately, help may be closer than you think.

A Research Project is Born

Amanda Rumore, Assistant Professor of Biology at Randolph College in Lynchburg, VA wondered about the best way to treat the pervasive skin condition that she saw on some of the horses she worked with while volunteering at Brook Hill Farm in Forest, VA. In speaking with other equestrians, Rumore discovered a wide range of home remedies for the malady. “A lot of them I thought were funny, sort of old wives’ tales. I started thinking it might be an interesting experiment to see if any of these home remedies actually worked on rain rot.”

Rumore’s interest led her to assemble a team to start the research project. Team members included her colleague Adam Houlihan, a microbiologist; and four Randolph College Students: Jessica Sidebottom ’17, Callan Frye ’17, Di Bei ’18, and Jacquelyn Parman ’18. Two of the students received grants from the Virginia Foundation of Independent Colleges to support the project.

What is Rain Rot?

Before we get into the procedures and results of the research, here are a few rain rot facts.

• Rain rot goes by many names: mud fever, crud, greasy heel, scratches, and pastern dermatitis. Mud fever, scratches, greasy heel and pastern dermatitis usually refer to the condition when it’s present on the pasterns. It’s most commonly seen on horses with white socks or stockings. Severe cases cause heavily keratinized lesions on the horse. Rain rot usually refers to the less severe infections you see on horses’ hindquarters and their sides.

• Rain rot is caused by the bacteria dermatophilus congolensis, and is often the result of a horse being in damp conditions. On the back and hindquarters, this is usually rain, humidity or bathing. On the heel and pastern, the condition shows up when horses are dealing with mud, heavy morning dew, or incomplete drying after a bath.

• It is completely bacterial; however, if the rain rot infection gets bad enough, the lesions will come off and allow a fungal infection to come in as a secondary infection. It is sometimes confusing, because in the severe cases, it is often a combination of bacterial and fungal infections, but it was started by the bacteria.

The Research Process

The project started with the team gathering information. After interviewing horse owners and veterinarians; reading articles, forums and blog posts, they had a list of suggested treatments.

“The most popular was mouthwash. Some people swear by the “brown” Listerine. Others believe that covering the rain rot with diaper rash cream is effective. Other people use baby oil. The one we found most interesting was the use of essential oils. Most of the old wives tales came from reading blogs and online forums where horse owners would post and say ‘I swear by this product or this home remedy’ We did specifically avoid using any products that contained anti-bacterials or antibiotics. We wanted to find something that was gentle and natural, but still effective”.

Rumore continues, “Once we had the idea, we split the project into 2 parts. We wanted to test the products in the lab, where we could quantify how effective they are, and we also wanted to treat horses with an actual infection, because a lot of the time you see results in the lab that don’t match on the horse or vice-versa.

“We started off by taking lesions off horses at Brook Hill Farm and then we took those back to the lab and cultured them. This was so that we could isolate the D. congolensis bacteria to use in the lab. Since it came from a horse with rain rot, we knew it would be an ideal specimen to use for our tests. Once we identified it and isolated it, because, obviously horses have a lot of other bacteria on them, we did testing which would tell us which of the products we were using were most inhibitory toward the bacteria. We did also use a control, which was stock strain you can purchase commercially, so it’s a purified bacterial strain. We compared the results from the organism from the horses to the stock strain, and we did everything in triplicate – so that we were sure the results we were seeing were actually statistically relevant.”

After that process was complete, the team focused on three commercial products, plus tea tree oil. Two of the commercial products were sulphur based and the third was a blend of essential oils. The fourth product the team used was their own development of 1% tea tree oil diluted in baby oil.

Once the treatments were chosen, Rumore and the students took them to the farm and applied one product to each of the subject horses daily for seven days. “We had a vet come out who scored the horses both before and after, so we could compare and actually quantify whether there was an actual improvement from the treatments.”

And the Results Please!

After a week of field testing and hours spent in the lab, the research team had their results. The two sulfur based compounds did not show much improvement; however, the tea tree oil and the other essential oils product did. Rumore shared, “In the end, we found that tea tree oil is the only remedy that worked both on the horses, and in our lab results.”

An Ounce of Prevention

In addition to avoiding damp conditions where possible, Rumore’s recommendation based on the research results, “As far as the solution – just a small spray bottle of 1% tea tree oil in baby oil. If you keep that around, you can swirl it around, and spray it on horses when wet humid weather is coming — you may be able to stop an infection before it starts. It’s hard to know when it’s going to start, but the earlier you treat it the better.  First time you feel a bump – treat it.”

Rumor continued, “Horse owners should treat rain rot as soon as possible. Severe cases probably still need to be treated with antibiotics from your veterinarian. If the lesions are coming off, we wouldn’t advise applying the tea tree oil to open wounds. That should most definitely be treated by a veterinarian.”

The team is hoping to publish the results of their research project in Equine Veterinary Journal in the next few months.

For more information on Randolph College, you can visit their website at To learn more about the programs at Brook Hill Farm, visit

Penny Hawes is a freelance writer and certified Therapeutic Riding Instructor from Monroe, VA. You can read her blog at or check out her website at