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| Poisonous Plants |
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There are a large number of poisonous plants and shrubs to be
found throughout Britain, although their abundance will vary greatly from
place to place. Horses and ponies at pasture are often at risk, especially
when grass is in short supply. Here is a guide to some of the more common
plants, how to identify them and their effects on the horse.
They are listed alphabetically, so click below if you are looking for a specific
plant or shrub to see if we have it listed.
Found in damp meadows and woodlands. The usual cause of poisoning
in the spring comes from eating the leaves and seed vessels and in the late summer
and autumn it is the flowers.
- Alder Buckthorn
- Bracken or (Pteridium aquilinum) is one of the
more common plants especially on some hilly or moorlands ground.
This is poisonous while green and remains so if cut in the green state, dried
and stacked. The roots or (rhizomes) are said to be five times more poisonous
than the fronds and this should be remembered if ploughing or digging land
on which bracken is growing.
The toxin in brackenfern is thiaminase, an enzyme that
destroys thiamine (vitamin B1). The horse then essentially suffers
from a vitamin deficiency of thiamine, which causes myelin degeneration
of peripheral nerves ( a loss of the fatty insulation layer to nerves
that primarily control muscles). Poisoning can occur at any time of
year, but is more likely in the late summer between August and October
when other forages are scarce and the level of thiaminase is at its
peak. Bracken is not considered palatable, but horses will eat it if
no other forage is available, or they will consume it in hay or bedding,
where it remains toxic. Some horses are believed to acquire a taste
for it, and these horses will consume it even if other forages are
available.
Horses need to consume bracken for one to two months prior
to manifesting clinical signs. After this time horses may then be fed
bracken-free forage and yet still develop clinical signs within 2 to
3 weeks. The first signs in horses is weight loss after a few days
on bracken. Later, weakness and gait abnormalities are present, which
progress to staggering, hence "bracken staggers". Affected horses may
stand with their legs widely placed and their back arched. Muscle tremors
and weakness is apparent when the horses are forced to move. Early
in the course of the syndrome, a slow heart rate and abnormalities
of the heart rhythm may be noted. Near the end of the clinical course,
the heart rate and temperature rise, and the animals cannot get up
and may have spasms and an upward arching of the head and neck. The
syndrome runs its course, with death occurring within 2 to 10 days
of the onset of signs.
First signs include:
In the advanced stages the horse may experience:
Horses can be treated if caught in time.
- Bittersweet Woody Nightshade (Solanum dulcamara)
Found in hedges, woods and waste ground. This plant is rarely eaten because of
its objectionable taste.
- Black Bryony (Tamus communis)
Another plant commonly found in hedges and open woods. Horses have died after
eating this plant from the hedge in their field.
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Click on Picture to Enlarge
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- Buttercup (Ranunculaceae family)
Frequently found in horse grazed pasture. Buttercups are potentially poisonous
because they contain a compound called protoanemonin, which is a powerful irritant,
causing inflammation or ulceration of the mouth, often with sorenes, increased
salivation and sometimes colic. However this usually causes the horse to stop
eating which makes this condition self-limiting, although it is always advisable
to contact your vet if you are concerned.
- Box Privet (Buxusa sempervirens)
This is most frequently grown as a hedge. However it is usually avoided because
it has a disagreeable odour when bitten. There have been recorded cases of horse
poisoning.
Another extremely dangerous plant, usually found in damp pasture.
The root or leaves can be fatal whether green or dry. This plant can be fatal
in a few hours, although survival of the first few hours can mean recovery in
a few days.
This shrub is commonly seen in parks and often found in hedges. The
leaves can cause cyanide poisoning.
Click
on Picture to Enlarge
- Deadly Nightshade (Atropa belladonna)
Normally found in hedges and wood clearings. This whole plant is poisonous. Typical
symptoms include dilated pupils and an inability to stand. However it is not
normally fatal to horses.
- Water Dropwort (Oenanthe crocata)
Also found in damp pasture. Poisoning usually occurs when the roots, which are
sweet tasting, are brought to the surface during drainage and ditching work.
Death is rapid.
This causes diarrhoea, abdominal pain, tremors and convulsions, however
is only usually eaten if found in hay.
Found in grassland, hedges and open woods. This plant causes photosensitation
in areas of unpigmented skin, so that when exposed to sunlight they become red
and irritated which leads to rubbing and possible infection. When dried this
plant loses 80% of its toxicity but can still be dangerous when baled in hay.
All parts of this tree are poisonous, in particular the bark and
seeds.
This shrub is commonly seen in parks and often found in hedges. The
leaves can cause cyanide poisoning.
Found in damp meadows and woodlands. The usual cause of poisoning
in the spring comes from eating the leaves and seed vessels and in the late summer
and autumn it is the flowers.
Believe it or not, many parts of the humble potatoe are poisonous.
Potatoe poisoning is caused by eating tubers that have decayed, sprouted or become
green through being exposed to sunlight. The green leaves and shoots as well
as the berries of the plant itself are also poisonous.
This is most frequently grown as a hedge. However it is usually avoided
because it has a disagreeable odour when bitten. The toxix glycoside is present
in all parts of this plant and the berries are particularly poisonous. Privet
poisoning though rare, can cause death within four to forty eight hours, so no
chances should be taken with privet. Fence off privet hedges and prevent access
to hedge clippings.
Found in grassland, hedges and open woods. This plant causes photosensitation
in areas of unpigmented skin, so that when exposed to sunlight they become red
and irritated which leads to rubbing and possible infection. When dried this
plant loses 80% of its toxicity but can still be dangerous when baled in hay.
Also found in damp pasture. Poisoning usually occurs when the roots,
which are sweet tasting, are brought to the surface during drainage and ditching
work. Death is rapid.
Another extremely dangerous plant, usually found in damp pasture.
The root or leaves can be fatal whether green or dry. This plant can be fatal
in a few hours, although survival of the first few hours can mean recovery in
a few days.
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Published
by J A ALLEN Price: £4.95
Published
by J A ALLEN Price: £4.95
Published
by J A ALLEN Price: £4.95
Published
by The Stationery Office Books Price: £11.75