Published October, 2013

Cleaning out the garage. Sorting through all the "stuff" in the attic. Shampooing the entire house’s carpeting. What could be a worse assignment? All of those tasks require lots of time, hard work, and are few people’s entertainment-of-choice for a weekend. Most horse people would rather saddle soap every saddle and piece of leather they own, or even wash and wax the horse trailer.

There is one horse-related duty that ranks right up there (on most people’s scale) with the above dreaded assignments--cleaning and disinfecting stalls. Who wants to strip totally every stall in a barn, wash, disinfect, and re-bed them all? That is a lot of labor most people would gladly put off for a nice trail ride. Plus, it’s not really necessary, or is it? Put yourself in these situations:

You are the owner of a boarding stable with 35 horses, primarily pleasure horses used for trail riding. After some horses return from a weekend ride, two horses develop profuse diarrhea. The veterinarian suspects salmonellosis and two days later confirms the diagnosis. How do you protect the other horses on the farm, including your own?

As manager and resident trainer at a hunter/jumper instructional school, you have horses and riders from throughout the country come to your facility to train. One day, a jumper develops a snotty nose and spikes a temperature. Within two days, abscesses start to form under the horse’s jaw--diagnosis, strangles. What will this do to your business and reputation?

You own one horse and proudly compete at county fairs and local horse shows. Besides vaccinations, how do you keep your horse healthy when you don’t know what was in that stall on the show grounds where you have to put your horse?

Disease outbreaks are dangerous to the health of your horses, and can be economically disastrous for your business and reputation. They can be personally devastating when the disease prevents you from competing in a long-awaited event and causes significant financial strain.

Why disinfect? Isn’t vaccination enough?

If only it were that easy!

First, no vaccine is 100% effective. Second, there are many more disease-causing organisms (pathogens) than there are vaccines. The table at left shows only some of the known pathogens of horses, and indicates those that commonly cause outbreaks of disease, or multiple cases on one farm. Many Gram-negative bacteria are present in feces and bedding, and are common causes of septicemia, which can be deadly to foals. These bacteria also can cause localized infections in areas such as eyes and joints of adult horses.

Of course, there are always those "mystery microbes" in the environment that cause respiratory disease, diarrhea, limb swelling, and other conditions that veterinarians recognize as being caused by infectious agents, but are unable to find the specific cause. They can’t find the exact cause usually due to limitations in current diagnostic tests. New bacteria and viruses are being found regularly with the advent of new microscopes and culturing methods. In 10 years, the list in the table will be increased—which is good since the more we know about the "bad guys," the more we can do to fight them and protect the health of horses.

Tough Bugs

Of the known common equine pathogens, clostridial organisms are the most difficult to kill because they are spore-forming bacteria found in feces and soil (organic matter). Clostridial diseases such as tetanus and botulism are individual animal diseases, and outbreaks are not common.

Of the contagious disease-causing pathogens in the table, rotavirus is the most difficult to kill due to its being a "non-enveloped" virus. The lipid envelope of other viruses is disrupted by a variety of detergents and disinfectants, enabling the virus to be killed.

Salmonella spp. also are difficult to kill, requiring thorough cleaning and stringent disinfection.

The follwing is an example of its resiliency: In one Swedish study, viable Salmonella cultures were obtained from dried cattle feces removed from a barn that had been abandoned for six years.

Rotavirus can remain infective after more than nine months.

Rhodococcus equi lives in the environment for years.

So, by identifying the horse’s bacteriologic and virologic enemies, and knowing that vaccination is useful, but not 100% effective, often the only way to prevent and control outbreaks of disease is through management and disinfection of the horse’s environment.

Notice: We did not say we are sterilizing or sanitizing the stalls. Rather, we are killing the pathogens as best we can with chemicals produced specifically for that use.

In the midst of a salmonellosis, strangles, or rotavirus outbreak, the best way to slow and stop the infectious chain of events is to kill the organism before it can contaminate another horse and cause disease.

What are we going to disinfect? This actually is an important question, and its answer dictates the types of disinfectants appropriate for use.

Many disinfectant labels state they are for use in hospitals, nursing homes, and health care facilities, with many people’s natural conclusion being, "If it is good enough to use in human hospitals, surely it is good enough to use in my barn."

But, what surfaces are being disinfected in hospitals? Stainless steel, glass, ceramic, linoleum, and solid plastics. Now, who has ever seen a horse stall made of glass and ceramic? Hospital surfaces are primarily nonporous and easily cleaned prior to disinfection.

Horse stalls are primarily made of wood or concrete block and might have some metal fittings and fixtures. Raw wood and unpainted concrete blocks are very porous and can trap and hide pathogens from disinfectants. This porous nature also makes the surfaces difficult to clean adequately.

There is a solution to this problem. Raw wood has to be cleaned of all debris. Holes and knots are filled with caulking or plastic wood, then a marine-quality varnish or polyurethane is applied to make the wood as nonporous as possible. Concrete block also can be cleaned and covered with two coats of enamel paint to make the surfaces easy to clean and disinfect.

What about floors?

Dirt, sand, or clay floors cannot be disinfected because they are soil (see disinfecting dirt sidebar at left). Removable rubber mats can hide many microorganisms beneath them, causing an increasing stench if not routinely removed and cleaned. Certain rubber mats can be placed and sealed along all seams and glued to the solid floor beneath, making them an excellent surface for the horse and stall cleaner. Asphalt or concrete flooring easily can be cleaned and disinfected, but can be hard on the horse’s legs.

So, our first objective is to have as many nonporous surfaces in a stall as possible.

Disinfectant Considerations

Hundreds of disinfectants are available commercially. How is anyone to know which ones are the best?

First, we know what major pathogens we need to kill, and we know the types of surfaces there are on horse farms . Second, we need to recognize where the pathogens are residing--in organic matter. Salmonella and rotavirus are in feces; S. equi is in nasal and abscess discharges; influenza virus and herpesvirus are in respiratory droplets. All of these materials (feces and discharges) are considered organic matter, which readily can inactivate some of the most potent disinfectants.

The situation is much different in a laboratory where a pure culture of bacteria is on glass or stainless steel. A disinfectant doesn’t have to deal with any organic matter--it just kills the bacteria on the nonporous surface. As we know, the situation is quite different in a horse stall!

In the real world, a disinfectant must be able to work in the presence of organic matter on contaminated surfaces. It must be germicidal against the pathogens encountered, and it must be biodegradable, cost effective, and relatively safe for humans and animals.

The disinfectant also must be able to kill pathogens in the water you have available. Water hardness is an indication of calcium and magnesium in the water. Those minerals can adversely affect the potency of a disinfectant.

Many disinfectants are labeled as to their effectiveness in hard water, such as, "Proven effective in 400 ppm water hardness." The abbreviation "ppm" means parts per million. This little fact is meaningless unless you know the hardness of the water on the farm. If you use city water, check with the water company on the average water hardness; if you have well water, contact the county extension service on how to get water samples tested. If you have used a disinfectant in your barn that only works to 400 ppm water hardness and your well water is 550 ppm, you’ve put a lot of money and labor into a cleaning effort that is not effective!

Choices, Choices, Choices

So, where do you find a disinfectant that will work given all these factors? There are many different classes of disinfectants, including phenols, iodophores (e.g., povidone iodine), hypochlorites (e.g., bleach), chlorhexidine, quaternary ammonium compounds, and others.

Phenolic compounds, recognized by the "-phenol" or "-phenate" at the end of the active ingredient names, will kill rotavirus, Salmonella, R. equi, and other equine pathogens in the presence of organic matter (see disinfectant protocol sidebar page 76).

Iodophores, such as 10% povidone iodine, also will kill rotavirus in the presence of organic matter, but usually are used as a surgical scrub and antiseptic rather than a stall disinfectant.

Although bleach commonly is used in human hospitals and laboratories, it is readily inactivated in the presence of organic matter and, therefore, is not suitable for use as the primary disinfectant on the farm.

Chlorhexidine does not kill rotavirus, but is useful for disinfecting surgical instruments and is used as an antiseptic.

Quaternary ammonium compounds, recognized by "-ammonium chloride" at the end of the active ingredient name, are inactivated in the presence of organic matter and do not kill rotavirus.

Pine oil, often used for its fragrant smell, is not useful as a disinfectant.

Keep in mind that disinfectants that are inactivated in the presence of organic matter might be perfectly useful for the countertops in the tack stall, cleaning out the refrigerator, and for other areas that are not heavily contaminated. However, for use in stalls, horse trailers, and aisleways that have heavy traffic and high levels of contamination, phenolic compounds work very well.

Two phenolic disinfectants with greater than 20% active ingredients are approved for use in Kentucky equine quarantine facilities: Tek-Trol (Bio-Tek Industries, Inc.) and 1-Stroke Environ (STERIS Corp.). Many other phenolic compounds are on the market.

Whenever you are comparing products, be sure to read the label for water hardness testing, organic load testing, biodegradability, proven efficacy against equine pathogens, dilution, and cost.

Roberta Dwyer, DVM, MS, Dipl. ACVPM, is a professor within the University of Kentucky's Maxwell H. Gluck Equine Research Center and editor of Equine Disease Quarterly.