The gleam and
shine in your horse's coat reflects his inner health, and puts a
sparkle in your proud eye. Invariably, there will be nicks and
scrapes to mar that perfection, but what about the times when
portions of your horse's hair are missing? Hair loss, also known
as alopecia, can be a frustrating management concern simply
because the reasons for its occurrence are so many and so
varied.
Tracking down
the reason for skin disorders often becomes an exercise in
sleuthing. One important element to consider is whether or not
your horse is itching and rubbing out the hair, or if the hair
is simply missing because of a disease or immune process that
attacks the skin. Let's look at some of the more common
syndromes that cause bald spots on your horse.
CLUE # 1:
ITCHING
Itching, or
pruritus, creates a self-inflicted hair loss. Not only should
you observe your horse's general behavior to see if he is
scratching himself, but you can scrutinize the skin for features
that hint at an itchy condition. Broken hairs cast a high
suspicion the horse is scratching the hair away. Reddened skin
or tiny scabs are not specific to itching, but might be part of
the rubbing process.
Biting Gnats
One of the most common causes of pruritus is an allergic
dermatitis caused by hypersensitivity to biting gnats (Culicoides),
popularly known as biting midges or "no-see-ums." The gnats
create a skin problem in the horse known as Queensland itch or
summer itch, seasonally associated with periods of high insect
activity. The surrounding environment has a lot to do with the
presence of these gnats in your horse's world. Culicoides
gnats prefer breeding in slow or still water such as that found
in ponds, small creeks, or springs.
These pests
tend to feed on the sensitive skin of the belly, inner thighs,
poll, mane, withers, and tailhead. Intense irritation created by
these insects stimulates a horse to frantically scratch on
anything in sight--a post, the side of the barn, feeders, trees
and bushes, or the ground. An initial hint that something is
truly amiss will be the glaring sight of the worsening "rat
tail" appearance of your horse's tail. A prized, flowing tail
might be rubbed out in just a few days as the horse vigorously
responds to the miserable itch. Often, the mane is also
mutilated and bald. Usually the rubbing starts out lightly, then
progresses as the allergic response progresses. As years go by,
susceptible horses tend to become more sensitized to the bites;
the condition worsens with more aggressive self-excoriation
(abrading away) of the skin and resultant larger areas of hair
loss.
Management of
this condition is possible. Affected horses should be stalled,
particularly during dawn and dusk when the gnats are most
actively feeding. Screens on the stalls are helpful, but the
mesh has to be small enough to prevent passage of the gnats.
Insecticide spray-misters also help in reducing the numbers of
gnats. Fly/mosquito sheets on the horses help to some degree,
but remember these bugs prefer the abdomen and thigh areas that
are not covered well by a fly sheet. Insect sprays containing
permethrin are helpful when applied regularly to susceptible
areas of the horse. Keep in mind that in many cases the gnat
might feed on the belly, but the systemic allergic response
creates itching specifically over the topline of the horse.
Treatment for
the condition relies on excellent management and insect control
strategies, but some horses might require systemic
administration of corticosteroids and/or hydroxyzine to control
the allergic response. In extreme cases, a severely affected
horse might need to be relocated to a different property away
from standing water and gnat breeding grounds.
Onchocerca
Infestation
Another itchy
condition that causes hair loss used to be quite prevalent
before the advent of ivermectin, and is caused by Onchocerca
cervicalis. This parasite enters the horse from a bite by an
infected gnat. The infective Onchocerca larvae migrate to
the nuchal ligament along the top of the neck, where they
develop into adults. Then they release microfilaria, which are
tiny filamentous larvae that infiltrate the skin of the horse.
Dead and dying microfilaria cause a mild pruritus and associated
hair loss, usually seen along the belly, withers, neck, chest,
and on the face. Sometimes you'll see depigmentation around the
muzzle or along the belly also caused by dying microfilaria.
Fortunately,
ivermectin has all but eliminated this skin syndrome in horses.
This popular deworming medication kills the microfilaria and
larvae, but not necessarily adults. The use of ivermectin two or
three times a year provides an effective control, and is
available over the counter where deworming products are sold.
Horn Fly Dermatitis
The horn fly bites horses to obtain a blood meal, and this is
associated with pruritus. Areas of hair loss will appear on the
side of the neck or on the underbelly of the affected horse.
Good fly control measures are important, while anti-inflammatory
corticosteroid ointments control localized irritation and hair
loss.
Lice Infestation (Pediculosis)
Lice by themselves do not cause immediate hair loss, but they
create an intense amount of pruritus and cause the horse to
scratch itself incessantly. With repeated scratching comes hair
loss. To identify if your horse has been infested with lice, see
if you can see lice marching through the hairs. A magnifying
glass is helpful in your visual search--pay particular attention
to areas beneath the mane, the shoulders, the back, and the base
of the tail. Spread the hair apart and look for dandruff-like
particles that move. These would be biting lice moving rapidly
away from the light. Sucking lice move more slowly, and you
might need to look carefully for their heads embedded in the
skin. The good news is that lice are species-specific, and
although a nomadic louse might walk upon you looking for a new
home, it'll retreat back to the safety of equine skin as soon as
it finds a proper candidate. Lice cannot survive more than one
to three weeks off their preferred host.
Treatment of
your horse involves bathing with appropriate medicated shampoo
products specifically targeted for louse therapy. The biggest
problem with this strategy is that louse infestation most
commonly occurs in winter or early spring when the horse sports
a thick coat; that is a difficult time of year to bathe a horse.
Lice cannot reproduce in or survive high body surface
temperatures that are prevalent in warmer times of the year.
Topical pyrethrin or permethrin products applied two weeks apart
are effective against lice, as is ivermectin given in two doses
two weeks apart. You should also clean the horse's tack and
grooming equipment with insecticides so he is not re-infected
after successful treatment.
Healthy horses
with adequately functioning immune systems seem to be affected
by lice less often. Situations of overcrowding, poor nutrition,
or poor environmental hygiene are stressors that set up
conditions for lice to flourish. Ample sunlight and regular
grooming are effective tools in minimizing the risk of louse
infection.
Mange
Mange is not a common condition in horses in the United States,
but should be considered in a horse which is very itchy and
losing hair. There are several types, named for the type of
mange mite that causes them.
Psoroptic
mange mites like to inhabit the mane, forelock, base of the
tail, or long feathers on the legs of draft-type breeds.
Chorioptic mange mites also have a predilection for the long
leg hairs. Demodectic mange is unusual in horses and is
seen mainly in immuno-compromised individuals. Sarcoptic
mange has been altogether eradicated in horses in the United
States.
Identifying
mange in horses requires examination of skin scrapings under a
microscope. The use of ivermectin is recommended in treating
mange mites, along with topical application of potent chemicals
that should be obtained through your veterinarian.
CLUE #2:
MISSING HAIR, NO ITCHING
Alopecia also
occurs because the hair simply falls out from inflammation
within the skin and/or hair follicles. Some of these problems
are of an infectious nature, while others are more innocuous.
Dermatophytosis
(Ringworm)
Dermatophytosis describes a skin infection caused by fungus. We
refer to fungal infections of the skin as "ringworm" since often
the lesions are oval or round in appearance. Fungi thrive in
dark, damp barns, particularly in autumn and winter months. Once
the fungus gets established on the horse's skin, a long winter
hair coat helps maintain the infection. Yet, the time of year
should not absolutely define the presence or absence of this as
a skin disease. Fungal infections can also become established in
warm, humid climates, particularly during fly season, and are
highly contagious--easily transmitted between horses by shared
tack and equipment.
The incubation
period for fungal infections takes anywhere from one to six
weeks. An infection might start with a hive-like lesion that
then becomes circumscribed in an oval shape. The lesions look
scaly and crusty, are accompanied by hair loss, and are commonly
seen around the girth and saddle areas, the hindquarters, and
along the chest, neck, and face. Sometimes the edges of the
lesions have frayed, broken, or distorted hairs just prior to
the hair falling out. Usually a ringworm infection is not itchy
or painful to the horse, but it can be. Young children are very
susceptible to ringworm, so care should be taken to keep them
from catching the disease by petting an infected horse.
Diagnosis is
best made by fungal culture; however, it can take as long as six
weeks to arrive at a positive culture. In the meantime, it is
best to treat the horse as if it had ringworm. Treatment
requires diligent attention to hygiene. All saddle pads,
brushes, girths, and cinches must be washed and disinfected, and
each horse should have its own designated equipment to reduce
the chances of transfer from horse to horse. Remove contaminated
bedding from stalls, and disinfect stalls and equipment with
bleach, chlorhexidine, or benzalkonium chloride. Isolate
infected horses from others.
Daily bathing
for the first week, then bathing once or twice a week is
necessary to control the infection. Weekly baths should be
administered until all lesions have been gone for at least two
weeks. The best disinfectants include tamed iodine shampoos,
chlorhexidine shampoos, dilute bleach (0.5% solution) rinses, 5%
lime sulfur solutions, and a fungal orchard spray (Captan) as an
effective rinse. During bathing, work the medicated shampoo into
the skin and allow it to remain for at least 15 minutes before
rinsing.
Topical salves
and ointments can be applied to small lesions. Useful products
include miconazole, clotrimazole, and thiabendazole. In extreme
cases that occur in immuno-suppressed or very young horses,
systemic antifungal medication might be warranted to help the
horse's immune system eliminate the disease. In most cases,
ringworm is self-limiting once the horse's immune system has had
a chance to recognize and process the infection. With the help
of good hygiene, exposure to sunlight, and frequent antiseptic
baths, most horses clear the infection within about six weeks.
Skin Scald
A common cause of hair loss on the lower legs is a result of
poor hygiene in the stabling or pasture area. Urine or manure
scald on the legs will cause hair to fall out from chronic skin
inflammation, usually accompanied by crusting and scabs in the
areas of patchy hair loss. The environment should be cleansed of
caustic irritants like urine, manure, excrement-soaked straw, or
soaked shavings. Daily cleansing of the lower legs will clear up
most of these without too much trouble. In some cases, systemic
antibiotics might be necessary. If you cannot point to damp or
dirty environmental conditions, have your veterinarian check
your horse for the presence of a bladder or urinary stone that
might be causing abnormal urination and scalding of the skin
where urine contacts it.
Rain Scald
Another cause of hair loss can be attributed to an organism
known as Dermatophilus congolensis, which elicits a
condition referred to as rain rot, rain scald, or dew poisoning.
This organism likes to infect traumatized skin, particularly in
the presence of high moisture. Young horses with poorly
developed immune systems are at a higher risk of getting rain
scald. Skin trauma can happen by abrasions, insect bites, or
constant irritation by frequent rain exposure that softens the
skin, particularly along the horse's topline. Often, the initial
lesions are seen along the rump, lower limbs, face, muzzle,
withers, and in the saddle region. This organism lives in the
soil as well as in the scabs of infected horses. Horses might be
"infected" with the organism, but show no outward signs of
disease. They still remain as carriers to high-risk individuals.
Rain scald
lesions are crusty and scaling and the hair pulls away with the
crust still attached, revealing an erosion beneath. Initially
these might start as raised tufts of hair with crusts. Usually
these lesions are painful. Unfortunately, crusting and scaling
abnormalities in the skin accompany many types of skin problems,
so the best way to diagnose Dermatophilus is to look under a
microscope at the cells obtained by a scraping, and to culture
the organism from a scraping. A biopsy of the tissue also gives
evidence of the cause of the lesions.
Patchy Shedding
In the spring, horses can experience a seasonal alopecia in
which large patches of hair shed out before entry of the new
hair growth, leaving a bald patch of skin. The area of naked
skin appears normal. Given patience, the hair will reappear
within about a month.
Sarcoids
Considered a benign form of equine skin cancer, a sarcoid also
creates hair loss. In many cases, sarcoids appear as flat,
hairless lesions with a scaling or rippled appearance to the
nude skin. These lesions are neither pruritic nor painful. The
most accurate means of diagnosis is to biopsy the lesion.
Sarcoids might
be infective from one horse to another if common grooming
equipment or tack is used. It is thought that the transfer from
horse to horse or soil to horse is by way of a virus. To limit
spread to others, practice common sense hygiene strategies in
horses with visible sarcoids.
A variety of
treatments are available, using methods such as cryosurgery to
freeze the sarcoid or direct injection of immune-stimulating
compounds (Cisplatin or mycobacterium cell wall fraction) into
the lesion or by repeated topical application of tissue-toxic
products (5-fluorouracil, Xterra) on the lesion.
Selenium Toxicity
In certain areas of the country where soil is rich in the
mineral selenium, some plants accumulate too much selenium in
their leaves, and horses grazing on these plants or horses fed
hay that has been grown in selenium-rich soils might suffer from
toxicity. Classic signs begin as a thinning of the mane and tail
hairs, with eventual hair loss on the mane and tail. In more
advanced cases, horizontal cracks will appear in the hooves,
with a potential to slough the entire hoof capsule.
Hair, serum, or
feed can be analyzed for selenium content. If selenium toxicity
is a suspected problem, affected horses should be removed
immediately from the offending pasture, or the hay should be
substituted with low-selenium hay from a reliable source.
An Accurate
Diagnosis
The diversity
of skin problems in horses is varied, and in many cases visual
inspection of the lesions might not accurately diagnose the
reason for the problem. The best means of identifying what is
wrong with your horse's skin is to have your veterinarian
perform a skin biopsy. A biopsy takes a punch of tissue through
all skin layers and gives a definitive diagnosis of the disease
process, and in many cases the source of the problem. In
addition, a skin scraping sample can be reviewed under a
microscope to determine cell type or identify parasitic
organisms, and/or a tissue sample can be submitted to a lab to
culture for a fungal or bacterial organism when appropriate.
These tests are simple to perform with minimal discomfort to
your horse. By pursuing this avenue of investigation, you'll be
able to address the nature of the skin problem and get the hair
and the shine back in your horse's coat as quickly as possible.
Tracking Your
Horse’s Hair Loss History
In considering the possible reason for a hair loss lesion on your
horse, ask yourself some very specific questions:
-
How
long has the lesion(s) been present on the horse?
-
In what
season did the lesion appear?
-
Where
are the skin lesion(s) located?
-
Where
did the lesion first appear?
-
-
What
does the lesion look like? Is there hair loss? Is it
red? Is it scabby? Is it crusty or scaling?
-
Is your
horse bothered by the lesion, i.e., does he scratch or
bite at it?
-
Are
other horses on the premises similarly affected?
-
Has the
horse travelled to different premises?
-
Has the
horse had any other medical problems?
-
Is the
horse on any medication?
-
What is
the horse’s diet (include supplements and horse treats)?
With these questions and answers in hand, you can begin a dialogue
with your veterinarian to better track down the source of the
problem. With an accurate diagnosis, you’ll be a step ahead in
effecting a cure.
