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EQUINE SHIVERS
A Practical Guide For Horse Owners
GUIDELINES ON ‘SHIVERS’ IN HORSES

A PRACTICAL GUIDE FOR HORSE OWNERS



Copyright 2011 by Brenda Bishop, VMD.  No portion of this publication may be reproduced, stored
in a retrieval system or transmitted, in any form or by any means, without prior written permission
of the author.  Portions of this work have previously appeared in Natural Horse magazine: volume
12 issue 2 (2010) “Demystifying Equine Shivers” by Brenda Bishop, VMD and volume 5 issue 3
(2003) “Deciphering Equine Fibromyalgia Syndrome (EFMS)” by Brenda Bishop, VMD.



Introduction

“The wagon rests in winter, the sleigh in summer, the horse never.”


Shivers is a hind leg unsoundness (a spasmodic condition affecting the thigh muscles of the
horse) that has been documented as early as the 1800’s primarily in certain draft horse breeds
and draft crosses.  Despite this historical record, many twenty first century veterinarians fail to
recognize and diagnose Shivers; at best, a peculiar lameness is noticed for which there is no
treatment coupled with the expectation of either no improvement or a gradual steady decline in the
horse’s usefulness.  In other words, a diagnosis of Shivers paints a picture of a one way street
and possibly a dead end street. (How hopeless for the horse!)  To make matters worse, from the
horse’s perspective, Shivers is just one clue about something we humans are probably not
seeing at all.  Perhaps it is time to shift our focus away from the lameness category and examine
the possibility of underlying autoimmune disease.

The average age of onset for Shivers is 2 to 4 years or older, and the vast majority of affected
horses are geldings or stallions.  Many times the horse is thought to have stringhalt, but a
thorough veterinary exam can help differentiate the two disorders.  Shivers is somewhat unique in
that it manifests sporadically and only while standing and (eventually) at the walk, most obviously
when walking in the backward direction.  The blacksmith will frequently comment that the affected
horse has unusual difficulty holding one or both hind legs up.  The affected hind leg will be held
spasmodically in a hyper-flexed position for several seconds before being placed on the ground.  
Careful observation will reveal fluttering eyelids and ears and possibly a raised tail at the same
time.  The horse will have episodes of resistance to moving the rear end over and backing up and
will leave no doubt in the handler’s mind that a gait deficit is present.  

Stress in any of its various forms will exacerbate the problem; for example, work in excess of the
horse’s fitness level, extreme summer or winter weather, traveling long distances, etc.  There are
many historical accounts of horses developing Shivers after a long train journey; likewise horses
shipped by cargo plane appear to be at higher risk for developing the syndrome.  Stress and
Shivers are such intertwined partners it is hard to tell how, when or where one stops and the other
begins. As the body’s immune system is pushed beyond its capacity to function in a healthy
manner, the system goes into overdrive, a serious imbalance is created and the body goes to war
against itself.  The end result is an immune mediated disorder.  Representative of such disorders
in horses are Myasthenia Gravis (MG), Lambert-Eaton Myasthenic Syndrome (LEMS) and
Fibromyalgia Syndrome (FMS).  Shivers plays the part of a leading actor in the scenarios
traditionally labeled MG and LEMS.  It plays a cameo role in FMS; occasionally it steals the show
but the potential for its appearance is ever lurking in the background.





The Myasthenia Gravis (MG) Horse

“Healing is a journey, not an end result.  Once an issue or situation is ‘healed’, it doesn’t mean that
this issue won’t show up again at a later time under different circumstances.”
Barbra-Ann King


When we critically compare multiple Shivers horses with each other it becomes abundantly clear
that several variations on the theme exist.  If an effective treatment approach is to be formulated
the management team (owner, trainer, veterinarian, blacksmith, body worker, nutritionist, etc.)
should be informed with rudimentary knowledge of what goes on at the cellular level.  Within the
autoimmune category (an overly stressed immune system attacks some of its own body proteins
producing antibodies) Shivers reflects a problem of neurotransmission, specifically at the
neuromuscular junction (NMJ).  At the NMJ, the messenger chemical Acetylcholine (also known
as a neurotransmitter) is released from small nerve endings, flooding the short gap (synapse)
between nerve endings and muscle receptors.  When a sufficient number of Acetylcholine
molecules can attach to muscle receptors, there is an electric discharge of the normal membrane
potential and the muscle fiber contracts.  If many or most of these receptors are already occupied
by antibodies, neuromuscular transmission is blocked.  This blockade is happening at the end of
the chain of transmission, a condition referred to as Myasthenia Gravis (MG).  In MG not enough
Acetylcholine molecules find receptors to trigger normal muscle contraction.  The muscle endures
a delayed irregular seizure type contraction which is uncomfortable (not to mention frightening) for
the horse and potentially dangerous for any human standing near the affected body part.  MG in
horses, dogs and cats is usually localized to the point of being organ specific and even tissue
specific.  For example, German shepherd dogs with MG will display an enlarged esophagus and
difficulty swallowing.  Horses with MG will primarily have painful muscle spasms and cramping in
their inner thigh muscles, historically called Shivers. The presence of Acetylcholine receptor
antibodies, skeletal muscle weakness, cramping within the inner thigh muscles and occasional
periodic sweating at rest characterize what we could call the ‘Post-synaptic Myasthenic Horse’.  

Current day symptomatic treatment of MG in humans, dogs and cats is based on knowledge of
the synaptic transmission of motor impulses at the NMJ by Acetylcholine.  To test the theory that
antibodies tie up muscle receptors, scientists have injected serum from a MG human into mice
whereupon the mice have promptly developed symptoms of MG.  Recent evidence suggests that
MG might be caused by a deficiency of Acetylcholine, i.e., by ‘Acetylcholine insufficiency’.  The
precise (ultimate) reason for dysfunctional synaptic transmission remains obscure.  Conventional
treatment of MG uses drugs which inhibit cholinesterase (the enzyme which breaks down
Acetylcholine) and which therefore serve to promote an Acetylcholine rich environment at the NMJ.  
Examples of such pharmaceuticals are: neostigmine, pyridostigmine, potassium chloride and
DMSO.  All are impractical for treating a large animal such as a horse.  Both neostigmine and
pyridostigmine, agents of transient action, have some limited value; for example, when a
blacksmith appointment is looming and the horse needs to be symptom free for a specific
window of time on a specific day.  In this case a dose of 1800 milligrams pyridostigmine orally in
the morning feed (using 60 milligram tablets) followed by a dose of 10 milligrams neostigmine
intramuscularly no less than three hours  prior to the appointment helps the horse dramatically
(as well as all concerned) but this approach is costly and requires coordination and timing.

The medical community agrees that MG frequently starts during or after a prolonged period of
intense stress, for example: emotional stress, malnutrition, chemical exposure, food sensitivity
and so on.  When prisoners of war in Singapore during World War II developed MG malnutrition
was suspected. After introducing a vitamin rich diet, these patients were restored to more or less
permanent remission.  Following the war Europe experienced a virtual epidemic of MG.  When a
highly nutritious diet was used, similar improvement was reported.  Nutrients generally accepted
as stress-protective include all the B vitamins, magnesium, manganese, copper, zinc, and
vitamins C and E.  They are some of the many vitamins and minerals involved in energy
production and neurotransmitter production.  

Vitamin B1 alone is exceedingly useful: it is key for the synthesis of Acetylcholine, it helps
Acetylcholine bind to receptors and it enhances the effects of Acetylcholine. Vitamin B2 plays a role
in tissue respiration.  Vitamin B3 helps nerve cells make serotonin, an important neurotransmitter.
Vitamin B6 also plays an essential part in the synthesis of neurotransmitters. (Many older
generation veterinarians believe that the thoroughbred breed, thanks to selective breeding, has a
higher requirement for B6.)  Vitamin B12 is a requirement for the synthesis of choline, a building
block for Acetylcholine.  Magnesium has multi-tasking down to a fine art; it activates many
enzymes.  At moderate levels it is energizing but at higher levels it acts as a muscle relaxant.  
Manganese is necessary for a healthy immune system; it has a role in the synthesis of
Acetylcholine.  Manganese deficits cause muscle weakness and disorders of the central nervous
system.  Copper is interesting in that women require more than men and many horsemen believe
mares require more copper than geldings and stallions.  Zinc reinforces the immune system.  
Excessive intake may compromise the absorption of copper.  Vitamin C alone has as much if not
more value than vitamin B1: in addition to promoting healthy muscle contraction and metabolism
and helping with neurotransmitter synthesis, it has (drum roll please) mild anticholinesterase
activity.  Vitamin E has a leading role in the energy metabolism of muscles.  A deficiency leads to
elevated muscle protein breakdown as in MG.  According to several published reports, human MG
patients have been successfully treated with megadoses (huge amounts) of vitamins B1, C and E.

The field of Orthomolecular Medicine originated in the early 20th century.  Some doctors were
prescribing vitamin supplements in megadoses by the 1930’s.  In 1967 Linus Pauling coined the
term “orthomolecular” to convey the concept “the right molecules in the right amounts”.  Today
Orthomolecular Medicine is defined as a form of complementary and alternative (and therefore
controversial) medicine that sometimes incorporates megavitamin therapy.  In the 1950’s
Frederick R. Klenner was prescribing megadoses of many vitamins.  Born in 1907 Frederick
Robert Klenner received his MD degree from Duke University School of Medicine in 1936.  He
eventually established a private practice in Reidsville, N.C. where he worked until his death in
1984.  He was inducted into the Orthomolecular Hall of Fame in 2005. In the course of some forty
years of general practice Klenner used vitamin C, often in conjunction with high doses of other
nutrients, to fight a number of illnesses, among them polio, multiple sclerosis and MG.  Klenner’s
patients lacked for neither hope nor vitamins with treatment schedules calling for massive
amounts of various B vitamins to “effect nerve repair”.  He was influenced by earlier work showing
that nerve degeneration results from multiple nutritional deficiencies.  Subsequently Klenner
would employ what may only be described as a wide ranging nutritional approach.  His protocol
for multiple sclerosis and MG is described in his paper, “Response of Peripheral and Central
Nerve Pathology to Mega-Doses of the Vitamin B-Complex and Other Metabolites”.  This same
protocol can be extrapolated for use in horses with extraordinary results.  For the average one
thousand pound Post-synaptic Myasthenic Horse on a healthy diet the following nutrients would
be added to the total daily ration:

10,000 IU Vitamin E           24 grams Vitamin B1                            2 grams Vitamin B2
1.5 grams Vitamin B3         9 grams Vitamin B6                           175 grams Vitamin C
50 grams Choline               3 grams Magnesium                        300 milligrams Zinc

Additionally, 10,000 micrograms (mcg) Vitamin B12 (for example 2cc of 5,000mcg/cc B12) can be
given intramuscularly 2 to 3 times weekly.  Loose manure from megadoses of Vitamin C is not a
problem because MG horses have a tendency toward constipation to start with and Ascorbic Acid
with wild Rose Hips (rich in bio-flavonoids) can be fed using time release 1500 milligram tablets
blended into hay cubes pre-soaked in water.  Injectable vitamins are impractical on a daily basis
and come with the added unnecessary risk of dangerous allergic reactions (anaphylactic shock).

In conjunction with megavitamin therapy, there are a variety of herbs suitable for use in horses
with MG that are useful for restoring and maintaining a healthy immune system.  For restoration
the combination known as Essiac Blend can be top dressed on the grain or added to soaked fiber
(beet pulp, hay cubes, hay pellets, hay stretcher, wheat bran, etc.).  It is comprised of Burdock (a
strong liver purifying and hormone balancing herb), Sheep Sorrel (a diuretic), Slippery Elm (for all
inflamed surfaces, nature’s chapstick), Rhubarb Root (a mild laxative) and Talisman.  For
immune system maintenance in a horse with MG, all of the following are of benefit: Horseradish
Root powder, Broccoli powder, Parsley Leaf powder, Red Clover Blossoms powder, Wheat Grass
powder, Cat’s Claw and Astragalus.  Astragalus is an adaptogen; it is respected as probably the
most important of all herbal deep immune tonics.  

Finally the MG horse will fare better if the caretaker remembers that MG has a tendency to
reappear in stressful situations, especially if the diet is unsuitable.  Usually the condition gets
worse as the day progresses.  Any planned activity that amounts to a stress should be scheduled
early in the day, such as transport, shoeing or trimming.  Denial of pasture access and heavy
exercise are both known to drop the bottom out of even a healthy horse’s circulating vitamin C
levels.  Aside from the main objective of stress reduction, pro-active immune support is helpful;
one option is once a month dosing with Colloidal Silver (60 milliliters of 500 parts per million
colloidal suspension orally or intravenously).  All vaccination and deworming programs should be
re-evaluated.  Research has shown that even routine vaccination exacerbates active MG in other
species.  Repetitive vaccination amounts to an immunologic challenge to the horse’s already
compromised system.  Serious thought should be given to any opportunity to minimize such
challenges.  Many deworming products contain ivermectin, a GABA (inhibitory neurotransmitter)
agonist.  Antibiotics belonging to the class Aminoglycosides are likely to cause problems if used
systemically, as they can cause neuromuscular blockade; examples from this group are
Gentamycin, Tobramycin, Amikacin, Kanamycin, Streptomycin and Neomycin.  Slightly less risky
are the Quinolone antibiotics (Ciprofloxacin), the Macrolide antibiotics (Erythromycin, Azithromycin)
and the Tetracyclines.  Drugs classified as steroids (dexamethasone for example) are
immunosuppressive and should be reserved for those horses that have lived with Shivers for
years; they have a place in critical situations but should be set aside once the patient is stabilized
and made reasonably comfortable.  





The Lambert-Eaton Myasthenic Syndrome (LEMS) Horse

“Good observation is your best tool.”   - Elaine Hammel, VMD


Working with the understanding of Shivers as a problem of neurotransmission at the NMJ it
becomes possible to differentiate a second clinical entity that we could call the ‘Pre-synaptic
Myasthenic Horse’.  When release of the neurotransmitter Acetylcholine from the nerve endings
into the synaptic gap is reduced due to antibodies against a membrane protein of those nerve
cells (the active zone of the pre-synaptic membrane), the consequence is interruption of
neurotransmission and eventually the typical myasthenic syndrome.  In MG the autoimmune
process happens at the post-synaptic location, at the Acetylcholine receptor sites of the muscle
cells.  When the autoimmune process takes place at the pre-synaptic nerve terminal the disorder
is labeled (in humans) Lambert-Eaton Myasthenic Syndrome (LEMS).  Interestingly the affected
human body parts are (primarily) the proximal muscles of the lower limbs (thigh and pelvis)
resulting in an abnormal gait.  Most patients are between 50 and 70 years old; LEMS is twice as
common in men as in women, the same ratio found in horses with Shivers.  A striking component
of LEMS is ‘anti-cholinergic syndrome’.  The LEMS horse likewise displays a multitude of
symptoms that would be expected in the presence of Acetylcholine insufficiency.  Whether the
absolute quantity of Acetylcholine is sufficient or not should not hinder our understanding of what
the outside of the horse is telling us.  A thorough assessment for clues will enable the observer to
correctly conclude whether a Shivers horse is Pre-synaptic or Post-synaptic. (The Post-synaptic
Horse is generally quite normal except for hind leg cramping.)  

In light of current research on LEMS in humans, the specific findings in a ‘Pre-synaptic Myasthenic
Horse’ are exactly as one might expect: any and all parts of the autonomic nervous system are
dysfunctional to one degree or another.  Those bodily functions that happen automatically in a
normal horse are now deficient.  Everyday caretakers have the responsibility of noticing all these
peculiarities which veterinarians can easily miss.  Even if everyone else misses the diagnosis,
the blacksmith will recognize the horse’s primary discomfort when trimming one or both hind feet.  
Over a long period (years) the horse will eventually demonstrate categorically that he has a
number of other symptoms.  The Pre-synaptic Horse prefers to dunk his grain and/or hay in a
water bucket.  Why?  Because he has a dry mouth (inadequate salivation).  Naturally he has a
predilection for choking on dry foodstuffs.  He tends to take a long time to eat for the same
reason.  His eyes are also dry due to reduced lacrimation (tear fluid production).  His manure
piles are scant.  Why?  He is chronically constipated.  He periodically hyperventilates at rest,
suggestive of a Chronic Obstructive Pulmonary Disease horse.  Why?  He has pulmonary muscle
fatigue which contributes to patchy sweating.  He has a shortened stride going up and/or down
hills.  Why?  Overall muscle tone is weak, especially in the hind legs.  Delayed tendon reflexes
ultimately lead to marked distension of the flexor tendon sheaths above the hind fetlocks.  Even
the muscles of the upper eyelids might be drooping.  Dehydration should be monitored when the
horse experiences excessive sweating at rest; a hot humid day can trigger excessive stress for a
body already at war with itself.  The history might include food allergies and sweet itch in summer;
various autoimmune problems tend to manifest in clusters.

One wonders what goes on at the cellular level to initiate such a host of LEMS-like issues in these
horses.  The primary disorder in LEMS is reduced release of Acetylcholine from the nerve endings
into the synaptic gap.  The body makes antibodies against a membrane protein of the nerve cells;
this type of membrane (called the voltage gated calcium channel) is affected by several classes of
neurotransmitters called neuromodulators.  Neuromodulation is a relatively new concept.  It can
be thought of as ‘neurotransmitters on assignment’, floating around in the cerebrospinal fluid,
influencing (modulating) the overall activity of the brain.  Some neurotransmitters are considered
to be neuromodulators, for example, serotonin and histamine.  Serotonin is famous for promoting
feelings of well-being.  It is found predominantly in the gastrointestinal tract of humans and
animals.  A smaller amount that is synthesized in the central nervous system has various
functions: regulation of mood, appetite, sleep, muscle contraction, memory and learning.  In
humans stress in the form of poor diet and/or lack of sleep ultimately leads to serotonin deficiency
(along with clinical depression according to most researchers).  Supplements that foster
serotonin synthesis and thereby plug the drain are: vitamins B3, B6, C and E, biotin, folic acid,
methionine, copper, iron, magnesium, manganese and zinc.  These nutrients can be termed
serotonin boosters; certainly most of them also have value as anti-stress nutrients.  The concept
of neuromodulation implies an amplified potential for positive changes that can be jump started
by using certain nutrients in certain amounts and ratios (and by extrapolation megavitamin
therapy).

Approximately two-thirds of Pre-synaptic Shivers horses are male.  Male horses have the sex
hormone testosterone.  Testosterone antagonizes serotonin.  Female horses have the sex
hormones estrogen and progesterone.  Progesterone is the best friend serotonin ever had; it is a
selective re-uptake inhibitor and an inhibitor of serotonin breakdown all in one.  Perhaps female
horses have a built-in protection mechanism against developing Shivers in the form of their
circulating estrogen and progesterone.  In fact, progesterone DOES have a well documented
neuroprotective effect, so much so that it is given to humans with massive brain trauma in those
cases so extreme that no other options are viable.  The Pre-synaptic Shivers horse can use all the
neuroprotection it can get.  (The problem is on the nerve cell side of the NMJ which is taking
orders from the central nervous system which ultimately involves the brain.)  Oral supplementation
with a 0.22% solution of synthetic progesterone, at the dose of 0.02 milligrams per pound of body
weight once daily will dramatically reverse all the symptoms displayed by a Pre-synaptic Shivers
Horse (of either sex) within two to three days.  How is this possible?  Progesterone boosts
serotonin levels which does much more than just make the horse feel peaceful.  Among other
things, serotonin has a direct effect on muscle contraction, it modulates skeletal muscle
oxygenation and it plays a role in sleep cycles (typically myasthenic syndromes get worse as the
day goes along).  But most impressively serotonin acts as a neuromodulator.  Neuromodulators
by definition influence both the release of neurotransmitter from the pre-synaptic nerve cell and the
post-synaptic cell’s response to the neurotransmitter, altering in a complementary way both the
input and the input-output relationship.    

Over the last several decades it has become acceptable veterinary practice to provide different
preparations of estrogen and/or progesterone to horses of both sexes for purposes ranging from
mood alteration (the lunatic stallion or the grumpy mare) to helping maintain muscle tone (‘loose
stifles’, weak back muscles) to attention deficit.  (More conservative over the counter oral
supplements promoted as ‘calming’ usually contain some combination of magnesium, vitamin
B1, tryptophan (a precursor of serotonin) and a wide range of herbs: chaste berry (vitex), skullcap,
chamomile, vervain, milk thistle, meadowsweet, passion flower or raspberry leaf.)  How can
administration of a hormone, progesterone, by boosting serotonin, a neurotransmitter, not just
make a moody horse feel better but thoroughly over-ride anti-cholinergic syndrome in the Pre-
synaptic Shivers Horse?  Serotonin must be operating in the role of neuromodulator.  This
premise can be substantiated when the hormone progesterone (with its ascribed  inherent
capacity for neuroprotection) is eliminated from the treatment plan completely.  By substituting a
combination of all serotonin’s next best friends into the same pre-synaptic Shivers horse the
same all encompassing improvement is achieved.  Of course by virtue of the fact that they are
friends as opposed to best friends they take an extra day or two to get the job done. Appropriate
daily supplementation for a one thousand pound Pre-synaptic Horse would be the following
serotonin boosters:

20 grams tryptophan                1500 milligrams vitamin B3           600 milligrams vitamin B6
12 milligrams folic acid           3 grams methionine                         1 gram magnesium
6 grams vitamin C                    65 milligrams copper                        275 milligrams zinc
250 milligrams manganese        4000 IU vitamin E

balanced with vitamin B1 (2 grams), vitamin B2 (500 milligrams) and choline (2grams) along with
serotonin allies chromium  (2 milligrams) and Ginko Biloba (500 milligrams).        

This formula works quickly (within about 72 hours) and efficiently for the Pre-synaptic Horse.  It
produces approximately a 25% improvement in the Post-synaptic Horse.

For the Pre-synaptic Shivers horse supplementation with serotonin boosters amounts to a fairly
sophisticated yet simple horse friendly approach. Unfortunately for the patient those bothersome
in-laws, the autoantibodies, are not leaving anytime soon.  Immunosuppressive drugs like
steroids and azathioprine can force their eviction within about six weeks but the total body will
suffer collateral damage in the interim.  A better treatment approach could more accurately be
thought of as ‘enhanced neuromodulation’.  Mechanisms for healing already contained within the
system are maximized while simultaneously a healthier immune system is enabled and
enhanced.  Long term considerations might include herbal additives and joint supplements.  Of
all the herbs that are used for mood disorders in horses, chaste berry (also known as vitex) is
arguably the most useful; it balances estrogen and progesterone in females and counteracts
testosterone (not a friend of serotonin) in males.  It is thought to have the added benefit of delaying
the onset of Cushing’s syndrome, another stress related scenario, in older horses.  Oral or
injectable glucosamine is a good pain relief strategy for the Post-synaptic Horse that competes on
a regular basis as well as for the average Pre-synaptic Horse.  Without question the most helpful
management practice for any Shivers horse is 24 hour turn-out, with constant grazing available.  
For horses and humans alike exposure to sunlight is a requirement of serotonin.  Humans are
not the only species to suffer from seasonal affective disorder (SAD).



The Fibromyalgia Syndrome (FMS) Horse

“There is one thing I always try to remember, especially when looking for quiet solutions to
annoying and dangerous problems.  That is, just like the old man <Walter Pruitt> said, the answers
will come if you ask the right questions.  The hard part is knowing the right questions to ask and
then taking the time to ask them.”
    - Mark Rashid             


Fibromyalgia in horses is in most instances a diagnosis by exclusion.  An afflicted horse is not
‘right’, nothing has been found to improve the horse, and specific symptoms are easily mistaken
for behavioral bad habits.  A thorough history becomes particularly useful ideally when it covers a
span of years.  Watching a FMS horse deteriorate is like watching grass grow.  In almost every
case there is an account of some (often forgotten) traumatic physical or emotional shock prior to
the onset of symptoms.  The classic example is the gelding that had a ‘difficult castration’.  
Performance horses that spend much of their lives in transit or in dusty stalls are prime
candidates.  Many times the history includes an episode of prolonged treatment with antibiotics
and/or steroids; the one infectious scenario that is not usually considered or easily documented
but is almost always present is an underlying chronic systemic low-grade fungal infection.  Fungal
infections in horses can be external, internal or both, acute or chronic, and more frequent at
certain times of the year, typically late summer and fall.  In every case, they are opportunistic by
nature; like rare orchids that require certain growing conditions, they thrive in environments
characterized by darkness, dampness, warm temperatures and low oxygen.  Examples of the
many acute (sudden onset) fungal diseases occasionally seen in horses are moldy corn
poisoning, Australian stringhalt, fescue toxicity and certain foal pneumonias.  In cases of chronic
(slow onset) fungal disease, when the possibility of a fungal component is targeted and
appropriate measures are instituted, the bulk of the FMS horse’s problems melt away within a few
weeks.  These problems fall into five general categories: cranial nerve deficits, microcirculatory
deficits, generalized chronic fatigue, endocrine imbalances and immune mediated sequelae.  
Due to the common denominator of stress, a complex immune mediated cascade of events can
set the stage for a specific autoimmune problem like Shivers to eventually make its appearance.

Typical of ‘flight or fight’ animals, horses react to stress with a natural reflex posture that can be
seen from afar.  They switch from the relaxed back, head down grazing stance to a hollow backed
high headed one.  Wild horses, dependent upon their ability to forage steadily and still get moving
quickly, alternate between these two frames continuously.  Domestic horses that are healthy and
stress free have little need for the flight stance.  Nevertheless, they respond to stress in the same
predictable manner.  Just look at a horse while racing, walking on sharp rocks or responding to a
drastic change in environment.  Horses with FMS are perpetually hollow through their toplines;
they can no longer carry any muscle mass over their backs due to skeletal muscle
deconditioning.  Similarly, deconditioning of pulmonary (lung) muscle amounts to loss of
compliance (ability to expand and contract) at the level of the alveoli, where oxygen exchange
occurs, producing bouts of asthma or COPD (heaves).  Breathing becomes hard work.  Cardiac
muscle weakness leads to mitral valve prolapse in humans and to aortic regurgitation in horses, i.
e., a loud diastolic murmur with or without left ventricular enlargement.  Chronic fatigue quite
naturally ensues.

Horses with FMS seldom have dapples (branches of the capillary tree of arterial oxygen rich blood
supply) because they have microcirculation deficits and poor oxygenation of tissues farthest from
the heart.  Low oxygen levels in the feet can result in persistent thrush around the frog, white line
disease and poor quality hoof growth.  Total body soreness might include the soles of the feet and
hypersensitivity to touch (grooming tools, insects) anywhere on the upper body.  Myofacial pain will
be manifested according to which cranial nerves are involved.  TMJ (temporomandibular joint) and
masseter muscle (facial nerve) pain can turn eating into a long distance marathon.   
Hypersensitivity to certain wavelengths of light (optic nerve neuritis) or sound (auditory nerve
neuritis) can result in head shaking or explosive behavior.  Loss of equilibrium (vestibular nerve
neuritis) eventually leads to stumbling, falling down, problems moving on sloping or uneven
ground, and problems standing up in a moving horse trailer.  Not surprisingly some individuals
start cribbing (a behavioral response which affords the horse some relief in the form of endorphin
release).  

To say that hormones and neurotransmitters enjoy a close relationship is a gross
understatement; the details of their interactions are varied and complex.  Within the category of
endocrine imbalances, different FMS horses can exhibit extremely low or high estrogen,
progesterone or testosterone levels, excessive sweating or anhidrosis, and/or insomnia (sleep
disturbances which contribute to chronic fatigue).  Chronic depression, mood swings or sudden
kicking episodes which have a biochemical basis will slowly escalate.  Horses that display a
shifting leg lameness (lame in one leg this week and a different leg next week) from front to back
and or side to side are nearly always FMS horses.  Small animal veterinarians dealing with
shifting leg lameness will quickly suspect an underlying infection; equine veterinarians are
cautiously reluctant in this regard.  (Immune mediated disorders are more commonly diagnosed
and treated in small animals than in horses.)  

Immune mediated neuritis in the FMS horse manifests most dramatically in the head area (cranial
nerve involvement) and the rear end (stringhalt).  Stringhalt usually has its origins in trauma to the
nerves supplying the lower cervical and upper thoracic portion of the horse’s nervous system.  
Time should be taken to differentiate stringhalt from Shivers.  The former is much more common
in FMS than the latter.  A temporary treatment for stringhalt (hyperextension of the hock and stifle
joints) is the antibiotic Doxycycline.  A dose of  2 milligrams per pound body weight in the feed
twice daily will reduce the severity of the problem within about ten days.  This is because
Doxycycline has an anti-inflammatory effect on immune mediated neuritis.  By the time stringhalt
or Shivers appear in a FMS horse veterinary intervention is critical.  The following protocol is user
friendly, horse friendly and effective: a double dose of Fenbendazole daily (4.6 milligrams per
pound) for 5 consecutive days followed by 15 days of Ketoconazole tablets in the feed (2
milligrams per pound) once daily.  Ketoconazole, a 200 milligram time release tablet, is quite
palatable and can be added directly to the grain without any extra steps for the caretaker.  
Fenbendazole in this instance is used to rejuvenate the lining of the gastrointestinal tract.  It strips
off the top layer of non-functioning cells in the large intestine, it has an escharotic (drying) effect on
any ulcers, it elevates the white blood cell count (the cells that fight bacterial infection), it
stimulates the immune system and it kills off any Candida overgrowth in the lower gut.  
Conveniently it also deworms the horse simultaneously.  Ketoconazole kills most garden variety
fungal species so efficiently that an ultra conservative dose is sufficient.  It has the added
beneficial side effect of lowering the horse’s serum cortisol, the stress hormone associated with
Cushing’s syndrome.  With serum cortisol out of the way healing can proceed naturally and
unimpeded.  Stringhalt in these horses will gradually resolve but a follow-up treatment regimen of
the appropriate nutrients in the right amounts will be necessary for the FMS horse displaying
Shivers.
Conclusion

“Still the question recurs “can we do better?”  The dogmas of the quiet past are inadequate to the
stormy present.  The occasion is piled high with difficulty, and we must rise with the occasion.  As
our case is new, so we must think anew, and act anew.”
   -Abraham Lincoln


Comprehensive maintenance plans for Shivers horses should include both near and far (next to
the skin and within a few miles) environmental considerations that have significant potential for
affecting overall health.  Horses living in the twenty-first century are subjected to stresses that
might not be recognized as such until a crisis has been precipitated.  For example, there is ample
anecdotal evidence that horse farms next to high voltage electrical power lines have more nervous
horses than those far away from such lines.  Horses stalled for long periods next to electrical
outlets can start cribbing for no apparent reason.  As a rule, the larger the species, the greater the
individual animal’s sensitivity to wave energy.  The long suspected ability of the larger mammals
to sense impending earthquakes and tsunamis is predictably reflected in their high survival rates.  
Researchers working with wild elephant herds in Africa have discovered that individual elephants
can feel the ripples of the earth’s surface from distant approaching friends or enemies through
their specialized foot pads.  Despite domestication, horses have not lost the ability to feel the
ground with their feet, a very important attribute for a prey animal.  

Similarly it is useful to consider that a horse’s sensitivity to invisible electromagnetic fields could
lead to aberrations in the energetic pathways throughout the body resulting in disrupted circuitry.  
However damaging this might be for the horse, such sensitivity gives the human caregivers
another chance to tip the scales in favor of a healthier equine nervous system.  The popularity of
magnetic wraps and blankets in recent years (for both calming effects and stimulation of blood
flow) suggests that external energy currents can positively impact internal currents; internal
currents involve the flow of electrolytes, for example, the calcium ion with a plus two charge and
the sodium ion with a plus one charge.  (Humans and horses are the only two large mammals
that produce copious sweat upon hard exercise with inherent potential for dehydration, electrolyte
loss and metabolic and/or respiratory acidosis.)  A practical application of this principle used to
the advantage of a Shivers horse is a ten day treatment regimen using a commercially available
adhesive skin patch imbedded with electrolytes.  The non-invasive patch is replaced with a new
one, using slightly different areas of the hindquarters, every twenty-four hours for a total of ten
days.  Extended benefits are gained by using this ten day protocol up to four times a year, and
eventually once yearly.  By helping the myasthenic horse achieve a more balanced flow of
electrolytes, the severity of clinical Shivers is reduced; substantial improvement is the norm with
this user friendly modality.   

All the same aforementioned long term goals of stress reduction and stress management apply
to the MG horse, the LEMS horse and the FMS horse.  Shivers can be effectively handled with
common sense environmental strategies and nutritional support, custom tailored to the particular
myasthenic syndrome at hand (either Pre-synaptic or Post-synaptic).  Once the immune system is
returned to a normal state of affairs, it is important to appreciate the potential for relapse if care is
not taken to safeguard the horse’s health.  In the particular case of a draft horse or draft horse
cross, a genetic pre-disposition to developing Shivers cannot be ruled out.  Consequently it
behooves any prospective new owner to question the breeder about the occurrence of Shivers in
any known family members as part of the preliminary information gathering process.  Any
consulting veterinarians might be asked to contribute their personal opinions about the horse’s
ability to back up and move the hindquarters over while standing quietly; this is easily incorporated
into the standard pre-purchase evaluation for overall soundness.     






This work honors those who have gone before us and continue to light the way: Joseph Haines,
DVM, Frederick Klenner, MD, Frank Palka, DVM, Ray LeRoy and Walter Pruitt.






Resources



Signal-Health (electrolyte patches)                    1-877-378-4946        
www.signal-health.com

Barbara Socha                                                   1-480-985-9515        
bsocha@signal-health.com  


Omega Alpha Pharmaceuticals                           1-800-651-3172        
www.oapharma.com

Puritan’s Pride (vitamins)                                     1-800-645-1030         
www.Puritan.com


Natural Path/Silver Wings (colloidal silver)            1-800-952-4775        
www.naturalpathsilverwings.com

Brenda Bishop, VMD        (author)                         1-910-783-9740         sporthorse@carolina.net






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