Summer
sun and humidity can increase the risk of three common skin conditions;
know how to prevent them and identify the warning signs.
Not
so Fun in the Sun: Equine Summer Skin Diseases
By
T.A. Banner DVM
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It's
that time of year again when all the flies, mosquitoes and gnats
decide to turn your quiet evenings into a swatfest and send
you running for the house. Unfortunately for your horse, living
in the great outdoors can mean dealing with environmental and
insect issues 24 hours a day in the humid Southeastern climate.
Horses are at increased risk for skin conditions in the summer
season. Probably the biggest take home message I can give you
is to start the appropriate treatment as recommended by your
veterinarian as soon as a skin condition starts. Don't wait
until the condition has worsened to the point of hair loss,
skin lesions and your horse has knocked over half the fence
posts in the paddock trying to scratch. Photosensitization,
rain rot (dermatophilosis), and equine insect hypersensitivity
are three common skin diseases. It is important to know the
clinical signs and causes of each.
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Photosensitization
Increasing day length brings increasing time under the
hot sun. Photosensitization is a common problem in horses
with pink or non-pigmented skin that is overexposed to
sunlight. The most common areas affected are the face,
nose and ears. In the summer, the intense rays of the
sun will cause the skin to burn and cause peeling of the
outer layers of epidermis. The skin is characterized by
redness, localized swelling, sensitivity to the touch
and could have weeping of serum. Photosensitization is
believed to be caused by phylloerythrin, which is a normal
breakdown product of chlorophyll in plants. The horse's
liver is responsible for excreting phylloerythrin and
any other plant chemicals that may ultimately damage the
skin. Certain plants, such as ragwort, St. John's wort
and buckwheat, contain chemicals that can damage the horse's
liver. This will cause the skin to be more susceptible
to ultraviolet rays from the sun. |
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Some medications, such as tetracylines, can make horses photosensitive.
A pink-skinned horse in strong sun is likely to suffer from
sunburn; but if that horse were being treated with photosensitizing
medications, it could suffer from a more severe sunburn. There
is a correlation between sunburn and liver damage with some
systemic diseases involving the liver making horses more photosensitive.
The best solution is to limit the skin's exposure to direct
sunlight but sometimes that is not possible. The use of sun
protection products is often necessary to keep the harmful rays
from burning sensitive areas. Many of today's grooming products
such as shampoos, fly sprays and coat conditioners may contain
sunscreens, and the protection provided by a sun block such
as zinc oxide is helpful. One of the problems is keeping it
on the horse because grazing and horseplay can wipe the product
from horse's face. The colored sun blocks may aid in determining
when it is time to reapply the product when viewing from a distance. |
Dermatophilosis
Dermatophilosis, "rain rot," "rain scald"
or "streptothricosis" is a skin disease usually
noted in prolonged wet conditions where high temperature
and high humidity are present. Skin lesions usually appear
as crust-like scabs or small 1/4 inch matted tufts of
hair over the rump and back, but can affect much of the
body. When rain rot appears on the lower limbs it is most
commonly referred to as "dew poisoning."
The organism, dermatophilus congolensis, which causes
rain rot, is not a fungus. It is an actinomycete which
has the characteristics of both bacteria and fungi. It
enters the follicle of the hair shaft and initially causes
small lumps on the skin or hair when running your hand
over your horse's coat. There are usually dozens of tiny
scabs that contain embedded hair and can be pulled or
rubbed off. Underneath the scabs, the skin is usually
pink with yellowish pus at the skin surface. The organism
damages the root and causes the entire hair shaft to lift
out in small clumps leaving the area hairless.
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Dermatophilosis,
also known as rain rot, rain scald or streptothricosis
is common in the Southeast due to increased humidity
and high temperatures combined with rainfall.
Photo courtesey of T.A. Banner, DVM. |
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The affected areas are often quite sensitive and saddles
and other tack must be carefully used. Since the area
becomes hairless then sun blocking products should be
used to prevent sunburn. The organism can be spread
through sharing of equipment between horses. This includes
saddle pads, blankets, leg wraps, brushes, halters,
etc. It is extremely difficult to prevent the spread
of rain rot, since a horse can pass it to another horse
by simply rubbing its skin on any object that the other
horse may touch.
The best prevention for rain rot is to use a disinfectant
on any equipment shared between horses after each use.
Dermatophilus congolensis grows better with a lack of
oxygen. Therefore, if your horse has a long, thick hair
coat, it will be necessary to body clip the horse and
remove any scabs that hold the organism to the horse's
skin. It is not a good idea to use ointments on rain
rot, because they hold moisture to the skin (and moisture
needs to be removed for the condition to cease). The
best treatment is to wash the horse with antimicrobial
and antibacterial shampoos and rinses.
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The
horse's back, rump, fetlock and the front of the cannon
bone are the areas most commonly affected by dermatophilosis.
Photo by Jill Haight. |
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Culicoides Insect Hypersensitivity
Culicoides Insect Hypersensitivity (CIH) is known by many
different names throughout the world (Sweet Itch, summer
eczema, Summer Seasonal Recurrent Dermatitis (SSRD), Queensland
Itch in Australia, Kasen in Japan and elsewhere as dhobie
itch), the symptoms are the same.
Culicoides Insect Hypersensitivity is a condition that
affects the quality of life of thousands of horses. CIH
is an allergic skin disease affecting susceptible horses
and ponies that become hypersensitive to the bites of
the insect of the genus Culicoides. The tiny insects are
commonly known as "biting midges," "punkies,"
or "no-see-ums" and are primarily active between
March and October, during the early morning and the evening.
Some sources report 120 or even 800 different Culicoides
species. Culicoides are very small and can pass through
conventional mosquito netting. They breed in aquatic habitats,
decaying vegetation, manure or water troughs.
They feed on the horse at specific sites, usually around
the tail head, under the mane, and underneath the horse's
abdomen. The allergic reaction, caused by the saliva,
develops at the site of feeding and the majority of affected
horses show skin lesions affecting the mane, tail, face
and ventral midline. The problem is characterized by intense
itching (pruritus), which results in rubbing and considerable
self-trauma, sometimes with secondary infection. Affected
animals are itchy, causing intense rubbing and scratching
on any available surface. Prolonged rubbing results in
crusting, scaling, skin thickening, hair loss and damage
to the skin. Mane and tail hairs may be broken and irregular
due to repeated trauma.
The symptoms are yellowish spots approx. 50 - 150 millimeters
in size, in many cases scratched open by the animals until
bleeding occurs. Crusts are formed, the mane and tail
hair being scratched and/or bitten away. In the crest,
hardened spots can appear and burst open which give it
a saw-like appearance. In the face, the hair sometimes
is scratched away and the black skin underneath becomes
visible.
CIH
is not contagious but other, healthy animals in the herd
might be affected as well because a horse with CIH will
scratch harder into the withers of a healthy animal due
to his own strong itch sensation and will in this way
do some damage to the other's skin and hair. History and
clinical cases among related horses give significant evidence
of a hereditary factor. It usually affects younger horses
but horses have been known to begin clinical signs in
their 20's.
Control of the condition is often difficult, with the
primary efforts directed at preventing affected horses
and ponies from being bitten, and symptomatic treatment
to control the irritating effects of the allergy. Your
veterinarian may also be able to do a blood test to evaluate
for CIH as well as other insect and environmental allergies.
As you can see there are many potential skin diseases
in the horse and several more that were not discussed
in this article. Living in a Southern tropical climate
exposes our horses to continuous challenges from insects
and environmental concerns. Remember to watch for early
warning signs of any changes in the skin of your horse,
and when noted, treat accordingly. It is also a good precaution
when buying horses in the winter to ask about skin problems
that could have been a problem the previous summer. You
can assume that a problem last year will most likely be
a problem this year. |
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The
areas of the horse that are most affected by CIH are the
tail and mane but the ears, poll, face, chest and ventral
abdomen may also be involved.
Photos by Jill Haight. |
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CIH
Prevention Tips
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1) Spray
and wipe down horse with insect repellents, especially in the
early morning and late afternoon.
2) Install a fan or be sure that your stall has plenty of airflow
since the small culicoides are not strong fliers.
3) Keep affected horses stalled in the barn from 6pm to 8am
to reduce exposure as culicoides are most active at dusk and
dawn.
4) Enclose the stall with a fine screen to prevent the entrance
of the insects into the area.
5) Cover affected horses with a "fly sheet" and "fly
mask" to prevent new bites.
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Horses
afflicted with CIH can benefit from being covered with fine
mesh "fly sheets" and "fly masks" to reduce
exposure to the biting midges. Cashel Crusader Pasture Bug
Armour is available with a belly guard, hood, leggings, and
tail guard for maximum coverage. For more information on Cashel
products visit www.cashelcompany.com.
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Toots
A Banner, DVM, from Micanopy, Florida owns Riverside Equine
Dental Services, a practice specializing in Equine Dentistry
serving the state of Florida. Dr. Banner can be reached via
email at tabanner@bellsouth.net.
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