by St John's wort
Q: My 20-year-old Mare has been diagnosed with St Johns wort poisoning.
She is in a pitiable state with a raw nose and terrible puckering
like corrugated cardboard on her white parts because of photosensitisation.
has seen her and she has had a course of antibiotics and a steroid
and intramuscular injection. She is in a dim stable with open access
to a small barn with sheets covering the windows to keep the light
I am walking
her in the evening and early morning out of the strong light and
am covering her with a tight woven cotton sheet when waking her
out. How soon should the corrugated skin starts sloughing off and
do horses normally recover? I know it is going to be a long process
but are there any ideas you can offer us to help?
am sorry that your horse is suffering form photosensitisation. St
John's wort (used to treat depression in humans) is one of the plants
that cause such conditions, but there are also many other possibilities
for such problems. Even plants like rape, alfalfa and clover can
cause similar disease when they produce chemicals that sensitise
animals to sunlight.
The most common
cause of photosensitisation is serious liver damage, such as that
caused by ragwort. In mild or moderate cases keeping the affected
animal out of the sun for one to two weeks is usually enough. This
allows the chemical causing the problem to be eliminated from the
In you case
you need to rely on the advice of your own vet because only he can
judge the exact seriousness and progress of the healing. Make sure
however that your horse is checked out for liver damage as the healing
process will take much longer if the liver is affected.
of disease only occur when up to 75% of the liver has been severely
damaged. Lastly, make sure that your horse does not have access
to St John's wort in the future. There are many different varieties
of this plant and some types do not actually cause much of a problem
as they contain very little of the key chemical hypercicin. You
might be interested to know that the hypericin in St John's wort,
which causes the problem of photosensitisation, is not actually
the part of the plant that gives most relief for depression in people.
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