Signs of EPSM in Draft Horses
by Beth A. Valentine, DVM, PhD
A suspected sign of EPSM is increased temperature (hyperthermia)
during recovery form anesthesia. The role EPSM may play in post-anesthetic
complications is particularly important, as draft horses have been known for
many years to be prone to problems associated with general anesthesia. The
results of this study may provide treatments for horses that would otherwise die
or be euthanized because of their inability to rise. Other signs include:
||Loss of muscle mass or conditioning, especially in the shoulder or hind
||Abnormal gait due to mechanical lameness in one or both hind legs. Abnormal
gaits possible in EPSM horses include:
Shivers: Affected hind legs are periodically flexed (bent) and
often held up for several seconds. This is most obvious when walking, backing,
and turning, but may also be seen when the horse is standing still. This may be
mistakenly called stringhalt, or the horse may be described as "stringy."
Fibrotic myopathy-like: Affected legs have a short, "stabby"
action with little or no bend in the hock and stifle. The horse often "slaps"
the ground. True fibrotic myopathy horses actually pull the hoof back several
inches at the end of the forward swing before slapping the hoof on the ground.
True fibrotic myopathy horses also often have a thickening due to scar tissue
from muscle or nerve damage that can be felt at the back of the stifle, where
the ham strings an the back of the thigh attach.
The lock may be prolonged, in which case, the hock and stifle are periodically
fixed in a straight position and the horse walks with the limb dragging behind
on the toe. The locking may also be short lived (called intermittent stifle
locking), in which case the stifle "catches" during bending and then
is flexed upward in an exaggerated bend very much similar to shivers.
||Trembling, especially after exercise.|
||Difficulty rising, backing, or reluctance to back.|
||Lack of energy.|
||Reluctance to pick up feet for shoeing.|
||Lifting or "stomping" of hind limb or limbs, especially while
||Episodes of colic, especially after exercise.|
||Slightly stiff, awkward, or short strided hind limb gait (often with no
||Lying down suddenly, unable to rise.|
Affected draft horses may appear completely normal for many years. Although
EPSM may result in slightly abnormal blood levels of muscle enzymes, some EPSM
horses have normal muscle enzyme levels. Diagnosis is best made by examining a
muscle biopsy for the characteristic changes. The biopsy is taken while the
horse is standing and sedated, and the site of the biopsy (the muscle of the
caudal rump) is injected with local anesthetic. Taking a biopsy is a simple
procedure that results in minimal scarring. Testing your horses for EPSM
provides valuable, perhaps life saving, information.
Further information: Data on EPSM Signs in
Beth A. Valentine, DVM,
PhD, is involved with EPSM research and other veterinary matters at
the College of Veterinary Medicine, Oregon State University. She is
this site's virtual vet and co-author of
Horses, an Owner's Manual.
This article appeared in
The Evener 1998