| Horses are living longer
than ever before, and with that rise in longevity has come an increase
in reported cases of Cushing's disease.
Equine Cushing's disease is caused by a tumor in the pituitary gland,
which is responsible for the production and regulation of hormones.
While the tumor itself is benign, the cells within the tumor produce
excess hormones, creating an imbalance in the horse's body. The cause of
the tumor itself is not known.
Cushing's Disease is most common in horses over 20 years old,
although the youngest documented case was found in a seven year old. It
is equally prevalent in both genders and is found more often in Morgan's
than in any other breed. Ponies may also have a slightly higher
predisposition.
The most notable symptom of Cushing's Disease is the growth of along
shaggy, coat of hair. This irregularly long and sometimes wavy hair
often persists throughout summer months and is a critical signal that a
horse may have Cushing's disease.
Other symptoms are caused by the hormonal imbalance in the adrenal
gland. These symptoms include excessive drinking and urination,
laminitis, and a tendency for recurring infections in the hoof (foot
abscesses), and a loss of muscle mass, especially along the top line and
rump.
Dr. Hal Schott, a veterinarian and associate professor of large
animal clinical sciences at MSU, is no stranger to Cushings Disease.
Last year, he completed the Michigan Cushing's Project, a study designed
to better understand Cushing's disease and the effectiveness of
treatment.
Realistically, said Schott,
"with Cushing's disease it's almost a visual diagnosis. When you
see the animal, you're highly suspicious it has the disease".
After identifying the visual symptoms, clinical testing can confirm
the diagnosis.
"Generally, we consider the overnight dexamethasone suppression
test to be the gold standard test," said Schott.
The dexamethasone suppression test, or DST, requires that the horse
gives a small sample of blood, then be administered cortisone, and a
follow up blood sample be taken the next day. The blood samples are then
compared to determine the horse's response to excessive cortisone.
Once a horse has been diagnosed with Cushing's disease, there are
treatments available that may improve the horse's condition, and in some
cases, even return it to normal health.
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Pergolide or cyproheptadine are the two most commonly used drugs that
have shown positive results in combating the effects of Cushing's
disease. However, until the Michigan Cushing's Project , no study had
ever been conducted to determine which drug was mot effective.
"We just did a simple project and asked the question,
"which drug is better for treating the condition"? said
Schott.
From late 1996 until 2001, Schott and his colleagues at MSU tracked
and compared the progress of horses treated with pergolide, those
treated with cyproheptadine and those with no treatment at all.
"We found clearly that pergolide was a much better treatment,
" Schott reported.
It seems to help them quite dramatically. It improves their clinical
signs, as well as reverses or makes their dexamethasone tests return to
normal in some, but not all cases.
Treating a horse with Cushing's disease does, however, come with a
cost. An average dose of pergolide for an average horse costs approx.
$60 a month. It also requires owners to administer the drug daily and
schedule regular appointments with their veterinarian for further follow
up blood work. If treatment is abandoned, symptoms can reappear s
quickly as two or three weeks later. Once on treatment, however, the
prognosis is optimistic for horses with Cushings disease. According to
Schott, more than 75 percent of horses are expected to improve in
response to pergolide treatment. After treatment has begun, Schott
reported that, "Many people have commented that their horses seem
three to five years younger". Because most horses with Cushing's
disease are already at an advanced age, three to five years can be a
significant amount of time to prolong their lives and continue to enjoy
their company. "The goal is to make these horses as healthy as
possible and as comfortable as possible in their retirement ages,"
Schott said. If owners suspect their horses may have Cushing's
Disease, they should continue to watch for symptoms, especially the long
shaggy hair and schedule an appointment with their veterinarian to
explain their concerns. Reporting symptoms and using the DST test are
the most effective ways to diagnose the disease early and maintain the
horse's quality of life. March 2002--Jeffrey Steadman, Dr. Hall
Schott, DVM.
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