are poisonous plants important?
- Poisonous plants are important because they
cause disease and death of livestock. Poisonings have occurred in the past
in which up to one million animals have died.
- The losses as a result of plant poisoning can be
direct or indirect and include death, loss of condition and ill-thrift,
poor production (for example, loss of milk yield) and reproductive failure
(abortions, stillbirths, birth defects, and failure to become pregnant).
- Further economic losses include the cost of
control and treatment measures (fencing, strategic grazing practices,
supplementary feeding, veterinary expenses, medicine), temporary or
permanent non-utilisation of toxic pastures and diminished value of
- There are serious health risks connected to
eating meat from animals that have died from plant poisoning.
- About 600 indigenous poisonous plant species are
known to occur in South Africa. Different parts of these plants (for
example, leaves, pods, seeds) may be poisonous.
- One of the greatest risks to farmers in South
Africa is the loss of livestock as a result of plant poisoning.
When is plant poisoning most
likely to occur?
Animals usually avoid poisonous
Generally poisoning occurs when:
- Animals are introduced into a new area (newly
purchased animals from other areas)
- There is a shortage of food and animals are
forced to eat the available fodder (during drought, after veld fires,
overstocking or during spring when poisonous plants are the first to show
Which factors contribute to
There are plant/veld factors and
animal factors, which contribute to the likelihood of plant poisoning
- After the dry season or a veld fire, poisonous
plants are usually among the first green plants to appear. A number of
poisonous plants are also at their most poisonous in the young stage when
they are most attractive to stock.
- Poisonous plants, which are not normally eaten,
are often eaten during times when grazing may be scarce such as
overgrazing and during adverse conditions.
- Some poisonous plants are very resistant to
drought and may be the only green plants avai lab le and are therefore
eaten during times of drought.
- Poisonous plants are often found as weeds in
harvested lands and along roadsides (areas that are frequently used for
grazing in times of scarcity).
- Certain poisonings occur after a sudden change
in the weather, usually after an unseasonable frost or when wet, cool
conditions are suddenly followed by a warm, dry spell.
- Wind and/or hail can knock acorns or pods to the
ground, making them available to animals.
- The use of fertilisers may increase the toxicity
of some plants.
- Animals are sometimes poisoned when feeding on
fodder (hay, silage, stover, concentrates) containing poisonous plants,
fungi or chemicals.
- When livestock have been kept in an area for
some time they are often familiar with the poisonous plants and will not
eat these unless forced to do so. Animals that are moved from familiar
areas to new pastures tend to graze less selectively and will get poisoned
- Poisoning often occurs when animals are moved
from one area to another I especially when they are allowed to
graze along roadsides where poisonous plants occur i n great numbers.
- Different species of animals are affected in
varying degrees of severity and by different types of poisonous plants.
- Exotic breeds of livestock tend to graze less
selectively, are more susceptible and are poisoned more frequently than
- Some plants affect males and females in
- Young and older animals are more susceptible.
The livers do not have the capacity to eliminate the toxins and young animals
also have not yet learnt to avoid poisonous plants.
- Hungry animals graze more greedily and are less
selective and therefore more likely to be poisoned. This can occur in
conditions of drought, veld fires or overgrazing.
- Thirsty animals look for plants with a high
moisture content, which they would normally avoid. Some of these plants
may be poisonous.
- Pregnant animals tend to be less selective and
have a higher intake than normal and may therefore be poisoned.
- Animals in poor condition are at a greater risk
of poisoning than animals in good condition.
- The skin colour of animals will determine the
extent to which certain poisonous plants will affect them, for example in
the case of photosensitivity (poisonings that result in damage due to
sunburn) unpigmented, white areas on the skin may become red and swollen.
important plant poisonings in South Africa
- Cardiac glycosides (for example, tulp and
In goats and sheep
- Cardiac glycosides (for example, tulp and
Effects of poisonous
plants in animals
- Many different types of toxins occur in the
various poisonous plants, which affect the body in different ways. For
example, some might affect organs such as the heart while others might
affect the liver.
- A single toxin can frequently target more than
one organ i n the body.
- When an animal eats a poisonous plant, it can
either die quickly, or suffer from a prolonged disease state.
- The various poisonous plants eaten can affect
the body in many different ways and some of the signs seen in animals
(depending on the organ or function of the body involved) include:
Restlessness, sensitivity to sounds
and touch, high-stepping, difficulty in walking, muscle tremors, aimless
wandering, staggering, stumbling, pushing against objects, star-gazing,
blindness, convulsions, paralysis.
Animal stops eating, salivation,
dehydration, fluid from the mouth and nose, vomiting, stomach pains, stomach
stops working, constipation, diarrhoea, swollen belly.
In dead animals large quantities of
fluid or gas in the gut may be visible, changes in colour and smell of the gut
contents, reddening of areas of the gut, bleeding.
Little or no urine production,
swelling of the belly with fluid, change in colour of the urine and the urine
may contain crystals (small stones) and the animal drinks a lot.
In dead animals crystals in the
kidney, swollen, wet kidneys filled with fluid, large and pale kidneys, change
in shape of the kidneys and bleeding may be observed.
Difficulty in giving birth, poorly
developed or large udder, enlarged belly, enlarged vulva, suppressed milk
production, abortions, deformed young, oversized or weak young, males not
interested in mating, repeated breeding.
When the heart is affected, an
animal may drop dead suddenly, for example, when it is chased or when drinking
The animal tends to stand with its
head in a low position and the stomach
tucked in. It sometimes grinds its teeth or groans, and the heart rate
increases. Bloat, diarrhoea and weakness of the hindlegs can also occur.
In the dead animal you may notice
pinpoint or larger areas of bleeding, lungs swollen with fluid, fluid in the
chest cavity, around the stomach and in the sac around the heart, froth in the
windpipe and a heart that is enlarged, flabby or pale.
Increased breathing rate, difficult
breathing, animal grunts when breathing, frothing at the mouth.
In dead animals fluid and gas in the
lungs, signs of infection in the lungs (pneumonia), and froth in the windpipe may
and blood-component signs
Pale, yellow, bluish or brownish
colour of membranes, green-tinged faeces, listlessness, animal stops eating,
animal will bleed easily, red-wine to coffee-coloured urine.
In dead animals you may notice ulcers
in the stomach, bleeding, and pale, yellow, blue or brown colour of the
Signs of bones and teeth
Itchiness and reddening of skin,
scale or crust formation, rough coat, thick fluid on the skin, seeds stuck onto
hair, wool or skin, sunburn, especially on white areas and muzzle, hair or wool
loss, animals seek shade, feet are warm and painful to the touch, hoof grows
outwards and turns up, difficulty in walking.
Some of these skin signs occur
because of liver damage.
Signs of bones and teeth
Uneven teeth, mottled or black
teeth, animal shifts weight from one leg to the other, stiffness, bones
Vomiting, weight loss, yellow
discoloration of membranes, swelling of the belly with fluid, sunburn, swelling
of the face, sore feet.
In dead animals you may notice
yellow colour of the carcass, bleeding in the body, fluid in the chest and
abdomen, hard and small liver, intense reddening of the liver, soft and swollen
liver, swollen gall bladder.
How do you know if your animals have
- The signs in sick and dead animals may raise the
suspicion of poisoning, and you may be aware of poisonous plants which
occur in the area.
- However, many of the signs can also resemble
those of other diseases.
- If you are unsure, your animal health technician
or state veterinarian can assist you. They may examine dead animals and
could send some samples to a laboratory for testing as well as search for
poisonous plants where the animal grazed. Once you know what type of
poisoning has occurred, you can decide on the best treatment and
plant poisoning be treated?
- In many cases there is no treatment for plant
- In specific cases there may be treatment
available (such as activated charcoal), but you first need to know which
type of poisoning has occurred.
- Although many animals recover, a number of plant
toxins affect the animals for the rest of their lives and growth and
productivity of stock as well as their resistance to other diseases are
- Poisoned animals have a better chance of
surviving if they are not forced to walk long distances.
- Prevention is therefore better than treatment.
How to prevent plant poisoning
- It is good to know which poisonous plants occur
in your area, and to keep your livestock away from the localities where
the plants can be found.
- Prevent overgrazing and veld fires.
- Keep animals in good condition with supplementary
food and licks during the dry season.
- Always provide water for livestock.
- Take care when introducing animals from other
areas (especially exotic breeds).
- It may be necessary to eradicate some of the
- Do not feed mouldy hay or hay cut from areas
with poisonous plants to your animals.
For further information about recognising poisonous
plants in your area, and about preventing and treating poisonings in your
animals, speak to your animal health technician or state veterinarian
Animal Health for Developing Farmers
ARC-Onderstepoort Veterinary Institute
Private Bag X05
Animal health for Develping Farmers Programme
ARC-Onderstepoort Veterinary Institute
Private Bag X5
Compiled by Directorate
Communication, National Department of Agriculture
in cooperation with ARC-Onderstepoort Veterinary Institute
Printed and published by National
Department of Agriculture
and obtainable from Recource Centre, Directorate Communication,
Private Bag X144, Pretoria 0001, South Africa