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The Horse |
Health Features - Poisonous Plants |
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New Zealand horses are at risk from
toxic plants both native and imported. Some plants which cause problems
to livestock overseas such as lantana, have not here, while the reed
canary grass which causes neurological disorders in some sheep every
year in New Zealand does not appear to cause the same issue overseas.
It is also important to recognise
that even some food plants can cause problems if overfed. To ensure that your horse is safe in
his paddock, use the following guidelines:
Plants may be toxic to animals for
a number of reasons. If a plant is unpalatable or causing
sickness in the insects and animals that would browse on it, then it
can be a great advantage for that species. On the other hand the
toxicity of the plant to mammals, or even just to horses, may be a by
product of producing substances which attract insects or animals to
its seeds or flowers.
The toxic substances in plants may be split into the following groups:
Toxic plants work in many an
various ways. Some will affect the central nervous system either
causing failure of the heart and respiration system or convulsions.
Other plants may cause eczema, photosensitisation, anaemia, weight
loss, irritability, diarrhoea or haemorrhaging. Toxins such as
oxalates may work by depositing crystals in the kidneys leading to
renal failure.
In many plants the concentrations of toxins in the plant may change during the life of the plant. Some are only highly toxic while the plant is fresh and can be safely included in dried feed. Others however, remain potent when dried. Foxglove for example can easily kill a horse if accidentally included in hay.
There is often the potential for
death if a horse is exposed to toxins, even when treatments are
available the outcome may be uncertain or permanent damage may have
been done, so prevention is essential.
The plants listed here are, of
course, not all of the plants in New Zealand that may be harmful to
your horse. Much of the information here is based on
H.E.Connor's "The Poisonous Plants in New Zealand" which is available
in most public libraries. Your vet, feed merchant and MAF should
be able to assist also.
Azaleas
 Castor Oil
Plant Ricinus
communis
Although all animals are
susceptible to poisoning from this plant Horses will suffer from lower
dosages. Both the leaves and beans will cause poisoning but the
beans are particularly toxic. As well as being toxic when
ingested the plants and beans are allergens which may cause nausea,
vomiting, asthma, irritation of the eyes, nose, ears and throat.
Symptoms:
Nausea, vomiting, drowsiness and gastroenteritis. In severe cases collapse is almost
immediate.
Foxglove
All parts of this widespread weed and
garden plant are very poisonous
Larkspur These ornamental
annuals are closely related to delphiniums, and all parts are
poisonous. Although larkspurs and delphiniums have no fleshy fruits,
they are so poisonous that even the pretty flowers could cause
illness if eaten. Commonest in colder areas.
Japanese Yew (all Yews)
Oleander
Poison Hemlock
Potatoes (as with
humans, the leaves and any green or sprouting potatoes are toxic)
 Privet
Ligustrum
Privet poisoning is not common
but the wide distribution of this invasive plant makes it a possible
danger. Both Tree Privet Ligustrum lucidum and Chinese
Privet Ligustrum sinense have poisonous leaves and berries.
The toxin glycoside is present in all parts of this plant and the
berries are particularly poisonous. The toxin affects both humans
and animals and any land owner is required to remove all privet from the property if
a health related complaint (respiratory problems) are received by the
regional officers.
Symptoms: Loss of power in the hind limbs, rapid pulse, pupils dilated. Death may occur within 48hours.
Ragwort
Senecio Jacobea
A native of Europe and Asia,
New Zealand feeding trials at Ruakura Station in 1902 were
instrumental in identifying Ragwort's as the cause of 'stomach
staggers'. It is a biennial herb which grows up to 1 metre
tall and bears bright yellow flowers each summer. Death from
ragwort poisoning may occur weeks after the animal has last grazed
ragwort as it kills through progressive and cumulative damage to
the liver. All parts of the plant are toxic, both fresh and
dried. In NZ Ragwort is a declared 'Total Control plant,
this means that each land owner\occupier is responsible for the
removal and control of all plants. If this is not undertaken
by the owner, Plant Pest Control officers will perform a pest
control programme at the owners cost.
How to get rid of Ragwort
- small infestations may be controlled by grubbing out
the plants, however it will regrow from any root fragment and no
plant material must be left onsite to dry out as animals will eat
the dried material. The best time to remove plants is during
flowering, the flower heads should be removed first and burnt to
ensure that seeds do not ripen.
Larger infestations will require chemical and\or
biological control. Blanket spraying in winter time is very
effective if followed up with spot spraying each Oct\Nov (pre
flowering) to catch mature plants that were missed.
Biological control requires the artificial spreading of the
Ragwort Flea Beetle.
Prevention is
hard, but good pasture management practices which ensure that the
soil is free draining, not overly fertilised with manure and
maintains a pH level between 5.5 and 6.0 will help minimise pest
plant invasion.
Other plants in the same
family: German Ivy, Groundsel
Symptoms:
Dullness, unsteadiness, aimless wandering, slow deliberate eating
of food, dark urine, yellowness of mucous membranes (jaundice).
Rhubarb - leaves or stems Sorghum
St John's Wort
Hypericum perforatum
St John's Wort causes hyper
sensitivity to sunlight. This can be particularly
troublesome in New Zealand's harsh sunlight, and in those spring
months when the ozone hole appears. White or light coloured
animals are most at risk (like any sunburn). The symptoms
are as for extreme sunburn with the skin splitting and sloughing
off in large chunks. An affected animal needs to be kept
completely out of the sun (even indirect sunlight) for a week.
Tomato Plants
 Tree Nettles
Urtica ferox (Onga Onga)
Common on the fringes of bush,
this plant is dangerous to horses and humans. Grows to 3
metres high, but more commonly 1-2 metres.
Horses have
been known to die quite soon after blundering into tree nettles.
Each of the needle like hairs can deliver an extremely painful
sting, not just the irritation of its other nettle cousins. The
sting is caused by formic acid and other chemicals present as a
tiny drop at the end of the hairs. Mild contact with Onga Onga
will result in extensive red rashes and blisters.
Other stinging nettles in New Zealand, Urtica
urens, Urtica dioica will sting but are nowhere near as
dangerous as the tree nettle simply because they are not as
large and horses are less likely to blunder through them.
Symptoms: Intense pain followed by convulsions and death.
T
 utu
Coriaria
The classic poison plant of New
Zealand. Although Tutu caused enormous losses of cattle and
sheep in New Zealand's early years, and continues to be highly
dangerous to a wide range of animals (including cats and pigs)
horses are rarely poisoned and are not attracted to Tutu.
However, when feed is low, be aware of the potential harm
this plant can do if you horse should decide to do some
experimenting.
 Yew
Taxus baccata
Poisoning by Yew is regularly
reported sometimes due to careless disposal of garden clippings or
from limbs blown from trees during storms which are not removed
from a paddock immediately. Animals have been known to drop
dead with the yew still in their mouths, this plant is
exceptionally toxic!
Symptoms:
Hyper excitement, nausea and vomiting, trembling, staggering and
death.
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| On This Page | |||||||||||
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Why is a plant Toxic? How do they work? Poisionous plants Ragwort Other poisons Regional Councils NZ Poisons Centre Links Books |
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Click on any thumbnail photo to view full sized |
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| Additional Poisonous Substances | |||||||||||
| Additionally,
here's a list of common plants and substances that are potential sources
of poisoning:
Arum lily All parts are poisonous, particularly the attractive spikes of yellow-orange berries. Likewise nearly all other members of this family have similar poisonous properties in all their parts. The toxins present mainly affect the alimentary system from the mouth downwards. Even a tiny part ingested can cause burning in the mouth and throat as well as stomach pains, the onset of these symptoms occurring dramatically and beginning within a minute or so. Fortunately it is very rare for horses to even vaguely interested in these plants. NOTE - The Taro is a member of this family! Taro is toxic if not cooked properly and should not be given to horses. Avocado skins, leaves and nuts,
Bracken
Pteridium aquilinum
Horses are more resilient to
bracken poisoning than cattle but it can still pose a serious threat.
When horses eat large amounts of bracken over a reasonably long period
of time it results in uncoordinated movements, muscle tremors,
convulsions and death. 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).
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. Although most horses will avoid it there is some evidence
to suggest that some can become addicted to it and will seek it out
once this occurs.
Newly grown fronds are the most toxic,
however 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.
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Symptoms:
Dullness, slow pulse, weight loss, lack of appetite, high temperature, muscle
tremors, convulsions,staggering (bracken staggers).
 Buttercup
Annulus
Buttercups of most varieties are
mildly toxic, although sometimes not when dried. Varieties such
as Spearwort are known to be be poisonous to horses. Waoriki is
a native species which is abundant in swamps, creeks and damp places
below 1000m. It is quite toxic and the chances of poisoning are
increased by its habit of growing in water.
 Celery-leaved
buttercup (Ranunculus sceleratus). This is one of the most toxic
species of buttercup. It grows in wet places such as in ditches,
along streams and around ponds and lakes. The parts most likely to
be put into the mouth are the glossy divided leaves which resemble
those of celery. Contact with mouth and lips can produce blistering,
but fortunately the bitter burning sensation usually prevents
material being swallowed.
Symptoms:
Colic, salivation, blackened faeces, bleeding and blindness.
Broom - The seeds are poisonous, especially if chewed and crushed before swallowing. The poisons are similar to those in its relation, the laburnum, but broom seems to be less harmful. Spanish broom (Spartium junceum) has larger flowers and is commonly grown in some areas although it has not naturalised extensively like the common broom. The seeds of the two species are similar and probably have similar poisonous properties, Cape honey flower, Cape weed, Cherry Laurel, Daphe, Datura, Hemlock, Hydrangeas, Goat's Rue, Italian Arum, Ivy, Karaka, Kowhai - The yellow seeds are very poisonous if eaten, but only if they are ground or crushed before swallowing. Otherwise, they pass through the digestive system and cause no harm Laburnum - The black seeds are very poisonous if they are chewed or crushed before swallowing, as with kōwhai. It mainly grows in the southern half of the North Island and in the South Island. Larkspur, lawn clippings, Linseed (must always be boiled, soaked or ground if it is to be included in feed) , Macrocarpa leaves, Mgano,
Oak (Quercus Spp) Symptoms: lack of appetite, staring coat, constipation followed by diarrhoea which may be bloodstained, abdominal pain, blood in urine There is no antidote. The horse is treated with drugs
to reduce the pain and control the diarrhoea, antibiotics may be
prescribed. Paspalum, Poppy, Ryegrass (a parasite can cause grass staggers), Jerusalem Cherry, Bittersweet, Thom Apple, Wild Parsnip.... Regional Councils - Environmental Services All regional councils in New Zealand provide information on pest plant control and most have free leaflets on various weed varieties. In addition most will have a wide variety of services to help you identify and control any pest species on your land. A network of plant pest control officers in each region can provide advice on effective methods of control, programmes planned for neighbouring properties and policy and procedural matters.
For Non-emergency information: 9am to 5pm week days Phone (03)479 1200 Fax (03)477 0509 or email poisons@otago.ac.nz TOXINZ is an Internet database containing information regarding toxic compounds and the management of poisoned patients. Reference photo galleries - toxic and common pasture plants
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| Links | |||||||||||
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Landcare New Zealand's guide to
Poisonous Plants,
you can also purchase a wall poster etc
Royal NZ Institute of Horticulture
- list of
poisonous plants
Small Farmer Magazine
- back issues index, including
information on poisonous plants
Massey University Databases online
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Pasture Plants
Weeds
Overseas sites - these still provide
excellent information, but do remember that some species may not exist
here, or may not be a problem here. Also remember that some of the
photos may show varieties that look different from those found here.
In New Zealand the Castor Oil plant is a deep rich red brown, however
photos on American or British sites may show the green variety.
Cornell University - an excellent site with clear pictures
Ontario Ministry of Agriculture, Food
and Rural Affairs -
Poisoning of Horses by Plants by Penny Lawlis, Animal Care Inspector,
OMAFRA, Komoka
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| Books | |||||||||||
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Poisonous Plants in New Zealand (Out of Print)
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