Sycamore poisoning and your Horse

Sycamore poisoning and your Horse
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Sycamore poisoning is a term which is
commonly used to refer to atypical
myopathy. The term is something of a
misnomer, as there are other ways a
horse might contract it than from the
sycamore tree. That said, the disease’s
scientific name now seems equally
inaccurate, as the disease is no longer as
atypical as it once was. Since the less
scientific term is the easier of the two to
remember, it’s achieved traction among
equestrian circles – but new evidence
suggests that another term might well be
more appropriate.
Among such circles, there are more
reports of the condition than ever before.
This increase might be due to an increased
awareness of the problem rather than an
increase in its actual prevalence –
nevertheless, it’s worth horse owners
acquainting themselves with the
symptoms of the condition and what can
be done to guard against it.
What causes sycamore poisoning?
The precise cause of sycamore poisoning
is a matter of some debate. One probable
clue to the disease’s
source comes from a
fruit that triggers a
disease with which
the disease is
associated, Jamaican
vomiting sickness, which is often triggered
after an animal ingests the ackee fruit.
Thanks to modern botany, we have quite
a detailed picture of the chemicals
contained in such fruits, and the
relationships they bear with the plants we
find in a typical horse’s environment.
The investigation was rapidly drawn to
hypoglycen A, a poisonous amino acid
found in the Ackee fruit. Sure enough, the
chemical was then found in box elder
trees around the sites of several
outbreaks of sycamore poisoning in the
US. The theory has been further
supported by subsequent studies on both
sides of the Atlantic, and we can conclude
with some certainty that hypoglycen A is
the cause of the disease.
When it finds its way into a horse’s body,
it begins to interfere with the production
of energy in the animal’s muscles,
preventing the mitochondria there from
properly oxidising fatty acids, and
preventing fatty acids from being
transported. The muscles affected include
those found in the cardiac and respiratory
systems, and thus the disease is extremely
serious.
What risk factors are there?
Since the sycamore’s seed is designed to
travel a long way as it falls to earth, the
chance of it finding its way into a paddock
is much higher than that of other seeds.
Consequently, the vast majority of cases of
sycamore poisoning in Europe have been
the work of the tree after which the
disease is named.
That said, there are several other trees
which contain hypoclycen a – including
maple trees. It is estimated that a horse
can develop toxic symptoms after eating
anywhere between 32 and 9,000 seeds –
but there is tremendous variation among
horses in terms of toxicity level.
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The disease is at its most prevalent during
wet and windy times of year – though, for
reasons we’ve already mentions, the
reason for this is more likely the latter than
the former. Fallen leaves and dead wood
on the ground will also heighten the risk, as
will a sloping pasture. It will come as no
surprise, then, that the overwhelming
majority of cases occur in the autumn,
when horses are grazing in the open in
paddocks with deciduous trees nearby.
Diagnosing the problem
Horses which are at risk will display several
signs before they develop severe
myopathy. These signs are all associated
with muscle weakness. They include
sweating, tremors and lethargy. If the
horse is also passing dark red/brown urine,
then this all but confirms the presence of
the condition – as there are few other
conditions which cause this symptom. A
vet will be able to perform laboratory tests
on a horse’s muscles. The main indicator is
the enzyme creatine kinase, which will
rapidly increase as soon as the myopathy
commences.
Prognosis
As you might expect, the prognosis for
horses diagnosed with sycamore poisoning
is invariably bleak.
Depending on the study you believe,
anywhere from half to a quarter to just 3%
of horses survive. We should treat these
findings with scepticism, however, only the
most effected horses will be submitted for
treatment.
Since it’s very difficult to tell whether a
horse has a good chance of surviving or
not, we should endeavour to be as
proactive as possible when treating the
condition. If the horse is to survive, then
they will generally begin to recover three
days after contracting the condition.
If you know what you’re looking for,
however, then determining the horse’s
chances of recovery is markedly easier. If a
horse is able to stand and pass faeces, and
the mucous membranes appear normal,
then the chances of a recovery are
generally good. It’s a good idea to monitor
the creatine kinase levels of the horse, too
– as a reduction will tend to precede a full
recovery.
Treatment
Treating the condition is an enormously
taxing endeavour – both physically and
emotionally. Affected horses will need
constant care, and ideally transport to a
dedicated facility. Wherever the treatment
takes place, it will typically be multipronged
and extensive.
Horses will need to be administered with
heavy painkillers. Fluid therapy may also be
necessary, as the horse will be unwilling to
drink. The fluid will need to be carefully
judged on a case-by-case basis, as some
horses will need more than others.
Horses will need to be fed a maintenance
diet as they recover, and given respiratory
support.
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While the horse is lying prone, they will
need to be regularly turned in order to
prevent muscle sores from developing.
Some vets may suggest a course of
relaxants – but this is controversial, as it
may exacerbate the condition.
Prevention
As we’ve seen, treating this condition is
hugely difficult, as not a great deal is
known about it. With more study will come
better methods and a better prognosis for
effected horses, but until that time comes,
the best approach is to prevent your horse
from contracting the condition in the first
place. Do this by minimising your horse’s
exposure to trees, frequently checking
your paddock for fallen leaves, and
reducing stocking density during autumn –
so that your horses are all able to access
the grass they need.
Beeston Animal Health Ltd.,
Whitchurch Road,
Beeston Castle,
Tarporley,
Cheshire,
CW6 9NJ
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