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Cushing's..
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| Long, non shedding coat | 80% |
| Muscle wasting | 60% |
| Chronic laminitis | 50% |
| Increased urination | 40% |
| Excessive sweating | 30% |
| Abnormal fat deposits | 25% |
The signs of Cushing's, which you will not be able to see, may be diagnosed by your vet. These may include increased PMOC, a depressed immune system, oxidative stress, reduced dopamine levels, insulin resistance and increased beta-endorphin in the spinal fluid.
Unfortunately accurate diagnosis is still difficult and but is important to decide whether you are dealing with Cushing's or IR.
There are a number of ways of testing for Cushing's. The two most
practical and accurate tests currently available are (1) the
dexamethasone suppression test, and (2) measurement of plasma ACTH
concentration. A new test has just been announced in the USA based on
domperidone stimulation. It is not available yet but could prove to be
useful in picking early Cushing's.
The dexamethasone suppression test is an overnight protocol in which a
pretreatment blood sample is collected in the late afternoon. A low
dose of dexamethasone is then administered by intramuscular injection.
A second sample of blood is collected the following day at around noon
and both samples are submitted for measurement of plasma cortisol. In
normal horses, administration of dexamethasone stimulates a
negative-feedback response that suppresses secretion of cortisol from
the adrenal glands. There should therefore be a much lower
concentration in the second blood sample. In horses suffering from
Cushing's disease, however, the negative-feedback response is blunted
and a lesser degree of suppression, if any, is observed.
Although it still the most widely used the dexamethasone suppression
test has drawbacks that limit its use: it requires two visits to the
farm by the vet, which increases its cost to the owner, many owners
and vets fear that administration of dexamethasone might increase the
risk of laminitis in a horse that is already predisposed to its
development.
The test may also be unreliable in the autumn in mares
due to normal hormonal changes bought on by the change in season. For
these reasons, there is an increasing move to the measurement of
plasma ACTH. This test involves collection and analysis of a single
blood sample; the pituitary gland in affected horses often secretes
excessive amounts of ACTH into the bloodstream as compared to normal
horses. While useful, this test is sometimes considered to be less
accurate than the dexamethasone suppression test, and blood samples
must be handled very carefully to avoid degradation of ACTH and
falsely low measured values. In human and canine Cushing's the ACTH
test is considered the gold standard. There is still uncertainly in
the equine world as to which is the best.
Treatment options.
Although there is no cure there is quite a lot we can do to help
improve or maintain quality of life of a Cushing's sufferer. There are
two prescription drugs commonly prescribed. These are pergolide (trade
names Permax) and cyproheptidine, but both have some reports of side
effects.
From a herbal perspective there are several things we can do to help
maintain or improve a horse's quality of life. Chaste Berry (Vitex
agnus-castus) has a long history of use in female hormone imbalance.
Its action in the brain is also similar to pergolide, in that both
bind to dopamine receptors. There have been a number of trials on
Cushing's suffers using Chaste which have demonstrated mixed results.
This may well be because the preparations used have been of
unspecified strength. It is therefore impossible to know how much of
the herb has actually been given. I read one report of a researcher
being told by the company making a Chaste Berry preparation that the
strength of the extract was commercially sensitive and that they would
not disclose it. Interestingly the same company told me they didn't
know the strength of their extract.
We have been using Chaste on
Cushing's cases for some time and although it doesn't work in all
cases the results have been very encouraging. We have typically been
using a dose of 20ml twice a day of a 1:2 extract.
Alongside Chaste other herbs to use should depend on the individual
case. For example Echinacea or Cat's Claw are often used to support
the immune system and Devil's Claw or Boswellia are useful when anti-
inflammatories are called for.
The whole question of the treatment of endocrine disorders is
difficult because a small change in hormone levels can have a
significant effect. Also the interrelationship of the different
hormones is very complex and in some cases not yet fully understood.
In conventional medicine the extremely delicate balances and small
amounts of hormone necessary to effect change make treatment
difficult.
The plant world however gives a class of herbs known as
adaptogens. These are herbs that supplement the body's ability to deal
with stress. This can be from anxiety, fatigue, or trauma which in
turn often results in stress on the endocrine system. Using the
problem of Cushing's as an example. The lack of domapine stimulates
glucocorticoid production by the adrenal cortex. The normal feedback
mechanism has failed so glucocorticoid production becomes excessive
resulting instress on the adrenal cortex.
Adaptogens are not one small type or predetermined mixture of herbs,
but a variety of plants that may be used alone or in combination. It
is thought that these herbs promote the balancing of the endocrine
(hormone) system and boost the immune system. In this way they help
promote and maintain homeostasis; the state of balance and stability
in the body.
There is a fairly wide range of adaptogens including some commonly
used herbs such as Ashwagandha (Withania somnifera), Astragalus
(Astragalus membranaceus), Siberian Ginseng (Eleutherococcus
senticosus), Licorice (Glycyrrhiza glabra) and Schisandra (Schisandra
chinensis).
There are a couple of things that are also useful and easy to do. The
oxidative stress can be helped by adding antioxidants to the diet.
These are readily available; one of the best is Rosemary. It can be
fed fresh or dried at a rate of about 30gms a day.
Fenugreek is a herb that is easy to include in the diet. It has been
well researched and has shown promise in the management of blood sugar
levels and insulin in other species, but no direct work has been done
on horses. The soluble fibre in Fenugreek seeds slows sugar absorption
and we know that it helps to maintain condition. It is generally known
that aging in humans causes changes in the gut. The most notably is
decreased gastric secretions and therefore decreased digestive
efficiency. It is also believed aging may adversely affect digestive
function in horses. One study showed digestibility of protein, fibre
and phosphorus were lower in horses aged over 20 than is was in horses
less than 10. Fenugreek is also mildly bitter and therefore stimulates
gastric activity. Something needed in older animals.
Unfortunately Cushing's seems to be becoming more widespread but since
the death of Barbaro from severe laminitis there has been a big
increase in the research effort into laminitis and Cushing's and
perhaps better understanding of these difficult problems will emerge.
Things to Avoid.
Phenylbutizone
It may be necessary for a horse with acute laminitis but it should be
used with great caution and only under the direct instruction of your
vet. If it is used on Cushing's horses it can cause additional
problems.
For minor aches and pains or chronic problems like arthritis, the use
of Devil's Claw or Boswellia are better options.
Yucca.
Yucca affects insulin and glucose levels and may increase problems for
horses with a history of laminitis or insulin disturbances.
Carbohydrates.
Such as...... grain and molasses.
As carbohydrates are digested, large amounts of glucose enter the
bloodstream. Elevated levels of circulating glucose can alter
secretion of cortisol, thus negatively affecting metabolism and
possibly contributing to the symptoms of Cushing's and triggering
laminitis.
Feed higher fibre in the diet such as soy hulls, beet pulp
and if more energy is required then oils can be added. But care should
be exercised as the feeding of oils have been associated with the
development of insulin insensitivity.
James Hart, Dip Herb Med, MNZAMH.
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