Page 183 - February 2021

small, firm lumps that may coalesce into a large plaque or line of bumps. With non- complicated hives, overlying skin appears normal with no hair loss and usually no itching. Hives are easily compressed, leaving behind a fingertip imprint of pitting edema, whereas other nodular lesions have cellular infiltration, such as scar tissue or a tumor, and are firm and non-compressible.
A typical hive bump takes 15-30 minutes to reach maximum size. Once the trigger event is gone, the hive usually only lasts
for an hour or so. In certain situations, the hive process may persist, with new lesions developing. An allergic response of hives is not usually associated with itching or pain, but in some cases, itching is observed.
One other type of allergic manifestation is a disease called atopy, which tends to
be a multi-factorial problem that includes
a genetic predisposition – Arabians or Thoroughbreds are reported at higher
risk. Typically, the problem shows up by
age 4, or if a mature horse is moved to a sensitizing environment. Atopy describes
a skin or respiratory allergic response to sensitizing antibodies in the environment, such as seasonal allergens like pollens, molds, grasses, weeds, trees, other insects, dust mites, or blanket or saddle pad materials.
WHAT TO DO FOR ACUTE HIVES
A horse that experiences an acute allergic response should receive veterinary care as soon as possible. While awaiting medical help, keep in mind that many horses with hives look bad but the horse doesn’t know there is a problem. For those that itch,
cool water soaks are helpful. It is best not
to medicate with drugs or apply topical medications so your veterinarian can see your horse in an unmodified state.
Hives rarely affect the general health of the horse and usually disappear within 1 - 2 days with no treatment necessary. In more severe cases, treatment may be indicated with
epinephrine and corticosteroids. Although antihistamines don’t seem to work very well for acute hives, an antihistamine like hydroxyzine may limit the allergic response.
Before implementing treatment during an attack, your vet will attempt to differentiate
an allergic response from infections such as
skin parasites, bacteria, or fungal (ringworm) infection since even a few days of corticosteroids can turn a mild infection into a severe case that is difficult to resolve. In most cases of ringworm, the hair falls out within a few days, whereas there is no hair loss with hives.
While hives are present on a horse’s skin,
it is common sense to refrain from riding him in active exercise. Sweat amplifies the physical discomfort a horse feels around the bumps, and saddle and tack further irritate inflamed tissue.
IDENTIFYING THE SOURCE
For a single occurrence of hives, you may never discover the incriminating source. However, if hives recurs more than once, tracking the allergen could be helpful. Consider changes in diet, environment, medications, vaccinations, or stress factors within recent months and provide your veterinarian with a list of suspicious items. Strategies for managing hives eliminate ingestion, contact, or inhalation of as many things as possible. With a little sleuthing
you may be able to identify the cause and successfully eliminate the problem from your horse’s future. Eliminate new medications or food supplements. Keep only hay in the diet, but you may need to change the source hay. Change bedding materials as well since some horses respond with hives to pine shavings.
A food allergy is most easily ruled out by feeding only hay (with no supplements) for at least 1 – 2 months. In some cases, a certain batch of hay is the source of the problem so you may need to substitute with hay grown by a different source or in a different field. Slowly reintroduce previously offered feed, one product at a time.
VETERINARY VIEWS
“A typical hive bump takes 15-30 minutes to reach maximum size. Once the trigger event is gone, the hive usually only lasts for an hour or so.”
“It is best not to medicate with drugs or apply topical medications so your veterinarian can see your horse in an unmodified state.”
SPEEDHORSE February 2022 181
Inflammation induced by allergens dilates small veins to increase capillary permeability in the skin. “Fluid” leaks into surrounding tissues to form wheals or plaques of edema, called hives.
Cool water soaks can help alleviate itching.
A food allergy is most easily ruled out by feeding only hay (with no supplements) for at least 1 – 2 months.