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Ragwort
and the Horse -
Do
horses actually eat it?
For many years it has been assumed that
horses will not eat green growing ragwort
plants but this is far from proven.
Indeed
it is only based on supposition that when
horses are grazing in a field in the mid
summer the ragwort appears untouched. The
biggest difficulty lies in the palatability
of the plant. In its green growing state
it is probably fairly unpalatable but the
wilted or cut and dried plant is.
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Thus
hay cut form a field with ragwort will be potentially
lethal. The repeated ingestion of a small amount
is probably the worst possible scenario.This
means that damage in the horse being fed hay
during the winter months made from unclean pastures
can cause damage. This is probably why most
cases of ragwort poisoning are seen in late
spring and early summer after a winter of ingestion.
What
does it do to the horse?
Ingestion of the ragwort plant (in any state,
in any amount) will result in the absorption
of the pyrrolizidine alkaloid that passes to
the liver in the portal blood vessels. On arrival
the toxin damages the liver cells to an extent
that is proportional to the concentration of
the chemical. Repeated and sustained ingestion
causes fibrosis and shrinking of the liver.
Once more than 75% or the organ is damaged irreparably
the horse will show the characteristic clinical
signs. These include lethargy, weight loss,
diarrhoea or at least pasty sloppy faeces and
in the summer months photosensitisation.
Perhaps
the most dramatic sign of hepatic failure is hepatoencephalopathy.
Here the chemicals that should be removed from the blood
by the liver, poison the central nervous system. Progressive
accumulation of these chemicals results in serious brain
disease, which shows as depression, abnormal behaviour and
sometimes even blindness.
How
can we diagnose the problem?
Ragwort is extremely poisonous to horses and even
small amounts can cause significant liver damage.
The liver has an enormous functional reserve (over
75%) and clinical signs of liver damage only appear
when there is less than 25% of the functional
tissue left. This can be some years later and
althought the liver can repair itself to some
extent it is also known that pyrrolizidine alkaloid
poison inhibits the repair mechanisms. Therefore,
repeated ingestion of even small amounts is potentially
very dangerous. The signs may only appear some
years later when the liver is beyond repair and
treatment.
While
the mildest signs of liver damage are not usually
detectable from the outside, damage to the liver
cells can be detected by blood samples.
Can
it be treated?
Liver failure can not be treated - it can only
be assisted to repair itself. Therefore once the
clinical signs appear it means that there is no
reserve of liver and that recovery is virtually
impossible. Of course, a few cases that have limited
damage do recover but if Ragwort toxins extensively
damage the liver then it will not repair effectively.
This
extract was taken from an article produced by
Derek Knottenbelt entitled 'The Latest on Ragwort'.
For
further information on Ragwort poisoning consult
your local equestrian veterinary clinic
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