Dew Poisoning/Scratches

A rose by any other name, said the poet, is still a rose. So it is with a form of dermatitis that afflicts the pasterns and fetlocks of horses. There is a wide range of names for this multifactorial affliction, but they all mean the same thing--a form of dermatitis that, at best, is uncomfortable for the horse and, at worst, can cause severe pain, bleeding, and lameness. Some call the affliction dew poisoning. Others use the term scratches. Still others refer to it as grease heel or cracked heel. There are yet others who call it mud fever. Whatever the term, the affliction is the same--a form of dermatitis that usually has its origin in a marshy or wet pasture and in unsanitary paddocks.


While scratches might seem a minor problem, it can result in permanent damage.

While all of the above terms identify the affliction, there are some who confuse it with photosensitization. Photosensitization is a somewhat similar problem but has a different cause, is manifested in a different way, requires a totally different form of treatment, and calls for different preventative measures. More about that later.

First, let's take a look at the condition that for purposes of this discussion we will call scratches, perhaps the most common name used for the condition. Now that we have finished bantering about the various identifying names and settled on one, it is time to take a look at what the condition involves.

Normally, the horse owner's first clue that a horse is suffering from scratches comes with the observation that there are crusty, crumbly, scabby bumps or lesions between the fetlock and the heel on the rear legs. Generally, the back legs only are involved, says Gunda Gamble, DVM, a native of Germany and now a general practitioner with her husband, Glen, in Riverton, Wyo. (Although the Gambles are general practitioners, they have a strong focus on equines.) However, she adds, the front legs are not immune from scratches. The problem can surface there, but normally the back legs are involved. It is rare, she adds, that only one of the rear legs is afflicted. Normally both are involved.

In the early stages of scratches, there usually is no lameness. As the problem progresses, with the lesions sometimes breaking open and bleeding, there can be soreness to the point that the horse becomes lame. The lameness often is most prominent when the horse is first exercised following a day or night of rest. As the horse continues to flex the pastern, the irritation sometimes lessens and the lameness decreases correspondingly.

In the most serious cases, the heel can crack open and bleed. If this occurs, there will be severe pain, with the horse often becoming dead lame and perhaps even going off feed.

Scratches is termed a multifactorial affliction, says Gamble, because the condition often involves four factors or stages.

Stage one involves a softening of the skin, when the horse resides in a wet or marshy pasture or is confined to a muddy paddock. In the latter stage of the softening process, the skin breaks open, opening the door for invasion by mites and other agents, which is stage two.

We should pause here and take a look at the mites that will be the invaders at this point. They are called chorioptic mites, which are 0.3 to 0.5 centimeters in length--certainly no giants. Small though they might be, they can cause immediate and long-lasting problems. The chorioptic mite feeds on epidermal debris, and in the process (in the case of scratches), causes irritation to the afflicted area. This mite differs from others of its kind in that it has legs that are short and close to its body, while most other mites have longer legs. The life cycle of the chorioptic mite normally is about two weeks and is completed on the host. Like most everything else in the equine world, there are exceptions to the rule. It has been found that some of these mites in various environmental conditions have survived for up to 69 days.

Mite populations usually are much larger during wet and cold weather. This means that clinical signs crop up among animals invaded during winter and spring. "This seasonality of mite populations and clinical signs is thought to be under the influence of temperature, humidity, and wetting of the host," writes Danny W. Scott, DVM, in the textbook, Large Animal Dermatology. "The disease often spontaneously regresses during the summer as mite numbers become very small. During this clinically inapparent stage of infestation, mites are more easily demonstrated around the coronet and interdigital areas."

It is important to understand, says Gamble, that the mite involved is not a blood-sucking creature, but is one that lives off skin flakes and hair follicles. This means that treating the horse, with, for example, an injectable remedy will not help. The mite must be attacked with a topical treatment to kill it.

The third factor that often is involved in scratches, says Gamble, is an opportunistic staph infection. It is the staph infection that causes the crumbly appearance of the skin and also produces the signature sweetish odor that is easily detected and used in making a diagnosis.

"You know that staph infection is likely involved," says Gamble, "when you pick off the crumbly skin and the hair comes with it."

The fourth component that normally is involved with scratches, she says, is a form of fungus. "This fungus is intradermal," she says. "Because it lives within the skin, we need to attack it with an anti-fungal agent that penetrates the skin."

Now that the skin has been invaded by bacterial and fungal agents, inflammation comes next. Gamble explains it this way: "All of these pathogens cause immune system responses by the horse, sending immune system cells and antibody complexes crowding into the area, creating further inflammation and irritation. When treating scratches, all of these factors must be kept in mind."

Normally, the veterinarian will make the diagnosis of scratches based on sight, odor, and history, but if one wants to have that diagnosis confirmed by a laboratory, it can be done. The problem with a laboratory diagnosis, says Gamble, is the time involved. A staph infection culture requires only 24 hours before results are available, but a fungal culture takes two weeks. Within a two-week period, the condition can worsen to the point of lameness. It is better, Gamble believes, to make a diagnosis in the field and begin treatment immediately.


Step number one in the treatment phase, says Gamble, is to change the environment. Generally, this means removing a horse from a wet area and placing it in one that is dry and clean.

Putting the horse in a stall that is bedded deeply with straw normally is not, however, the first step of choice, Gamble says. For one thing, straw can be abrasive to what is now very soft and tender skin. For another, straw often is loaded with fungus and this can increase the danger of further infection.

"If the horse is to be stabled," Gamble recommends, "the bedding material should be shavings or perhaps peat moss."

The Gambles have developed their own particular treatment formula and protocol for scratches. It is designed to meet all four factors involved--the softening of the skin due to wet conditions, the invasion by mites, the staph infection, and the fungus.

Before applying their particular remedy, they recommend that a couple of preliminary steps be taken. Once the horse is in a dry environment, Gamble advises, gently clip the area afflicted. The area shouldn't be shaved, just clipped, she says, because shaving would leave no defenses against further abrasions to the soft and tender skin.

Once the area is clipped, she suggests that it be washed with a chlorhexidine solution such as Novalsan. Chlorhexidine is an antibacterial solution that is highly effective against a wide range of gram-positive and gram-negative agents.

Once the afflicted area is properly prepared, it is time to apply a substance that will attack the problem on all fronts. The formula, as prepared by the Gambles, includes scarlet oil, which serves as a binding agent; chlorhexidine, which is anti-fungal; DMSO, which allows the penetration of the skin as well as serving as an anti-inflammatory; and nitrofurazone, to attack the staph infection.

The best method of application, says Gamble, is to soak several squares of gauze in the solution, place the squares over the affected area, and hold them in place with a snug--but not tight--wrap.

The treatment concoction the Gambles have developed serves as an effective anti-fungal, anti-bacterial, anti-inflammatory, and anti-parasitic mixture.

Beneficial results will be observed almost immediately, says Gamble, but this does not mean that treatment should be halted. To make certain that the problem has been totally cleared up, she believes, the treatment should be continued for about two weeks with the horse remaining in a dry and sanitary environment during that time. During the treatment period, she recommends, the dressing should be changed every couple of days.

"Dealing with scratches can be a real pain," says Gamble. "It is a condition that does not go away easily. It takes work."

While scratches might be more prevalent in areas where there is a lot of rainfall, along with heavy dew, no locale is exempt. The condition, for example, shows up with some frequency in arid Wyoming in those parts of the state where pastures are irrigated. Horses maintained in dry, desert-like, non-irrigated areas in the state will seldom be afflicted with scratches, although there are no guarantees that the condition won't surface even in those locales.

In her native Germany, says Gamble, the condition is found most frequently in draft horses, particularly those with heavy fetlock feathers, such as the Friesian.

However, she adds, she sees the condition in the general horse population in the United States more frequently than she did in Europe. The reason, she feels, is that space restrictions require that many European horses be stabled. Conversely, more U.S. horses, especially in the Western states, are kept outdoors even during muddy, wet, winter days and during early spring when rainfall is heavy and pastures might remain wet and soggy for long periods.

The question often debated is whether scratches shows up with more frequency on white feet as opposed to dark. It often appears that this is the case, says Gamble, but she wonders if it isn't more a matter of observation than occurrence. Scratches, she points out, is more easily seen against white hair and pink skin than against black hair and a darker skin. Thus, the horse owner would be more apt to see the condition and seek veterinary assistance when white feet are the ones afflicted.

She believes that there is no difference in occurrence, only in discovery.

While a veterinarian normally will be able to diagnose scratches quickly, says Gamble, there can be confusion with some horse owners between that condition and photosensitization. With photosensitization, only the white feet are involved.


"Photosensitization is often not recognized as such by horse owners," says Gamble. "It may only show up as a small patch of scabby crud on a white foot, or it can affect all areas of white hair. The skin under white hair is non-pigmented, and the lesion is actually a burn. The problem occurs when photodynamic substances in the feed (rich alfalfa or clover) are deposited in the skin and react with sunlight, causing a burn."

Horse owners quickly can learn to tell the difference between scratches and photosensitization, she says, if they remember that scratches will always have bumpy, flaking skin in the affected area, and with photosensitization that will not be the case. Instead, the skin will literally appear as though a hot object has been placed against it and produced a burn.

Treatment for photosensitization, Gamble says, involves getting the horse off alfalfa, applying sunscreen in some instances, and, in severe cases, completely restricting the horse from sunlight, and administering antibiotics.

Lesions resulting from photosensitization, says Gamble, also can be found on the face and, if severe enough, anywhere on the body where there is non-pigmented skin.

Fortunately, both scratches and photosensitization can be cleared up with treatment. Normally, scratches is the easier affliction to treat. Once the horse has been placed in a dry environment and the bacterial and fungal attackers eliminated, healing comes quite rapidly. In addition, with the arrival of drier months, the risk factor diminishes. With photosensitization, the non-pigmented skin always will be at risk when diet and sunlight reach a certain combination level.

In both cases, observation of the horse is essential if the conditions are going to be detected before reaching the serious stage. This especially is true with scratches. Detecting the condition when only light bumps and some dry skin have appeared facilitates early treatment and fast recovery. Treating a horse in that condition in the manner that Gamble recommends can bring almost instant beneficial results.

However, if the condition is not discovered until severe lesions have developed and the horse is lame, the treatment program can be more involved and lengthy. While scratches might seem only a minor problem in the grand scheme of things in the world of equine health problems, it can, if left untreated, result in permanent damage.

Providing a dry, clean environment obviously is the best preventative measure. However, this is not always possible. What is possible is ongoing observation of the horse and its condition and immediate care and treatment when scratches is discovered.


Gunda or Glen Gamble, DVM, 2-Heart Veterinary Clinic, Riverton, Wyo. 82501; 307/856-7764

Danny W. Scott, DVM. Large Animal Dermatology. W. B. Saunders Company, Harcourt Brace Jovanovich, Inc., Philadelphia, Pa.

M. Horace Hayes. Veterinary Notes for Horse Owners. Arco Publishing Company, Inc., New York, N.Y.

About the Author

Les Sellnow

Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at or by calling 800/582-5604.

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