Poisonous Plants & Toxic Compounds

Listed below are some of the most commonly encountered poisonous plants and toxins that cause issues with companion animals and livestock.

If you are concerned that your animal has had access to any of these poisons, or if they are showing signs that can be attributed to any of these compounds, please contact your vet as soon as possible, as early intervention is usually required if a positive outcome is to be achieved.


Macrocarpa and Pine

MacrocarpaPlant description

Macrocarpa: Evergreen with red-brown bark. Up to 25m tall. Produces 2-4cm cones and thin leaves
Pine: Up to 60m tall. Pine needles found in clusters of three. Produces cones that are egg-shaped and approximately 12cm long

Animal species affected

  • Cattle
  • Pine may affect sheep

Symptoms of poisoning

Macrocarpa causes depression in adult cattle, followed by abortion late in pregnancy. The abortion may be followed by retention of the membranes. Deaths can occur. 

Pine needles may cause abortion on death in cattle, but this is anecdotal. Otherwise dehydration, loss of condition and lethargy seen. 

Treatment and prevention

Prevent access to adult cows in late pregnancy, and take care of following storms, as branches may be blown into the grazing area. 

Vet check any animals showing signs of illness



RhododendronPlant description

An evergreen shrub, 1-5m tall. Oblong, smooth, shiny leaves. Clusters of flowers of various colours. Popular garden shrub

Animal species affected

All species - goats fond of eating this plant

Symptoms of poisoning

Salivation, vomiting greenish froth, colic, constipation/diarrhoea, trembling, lying down, death


Prevent further access to plant and call vet Ensure clippings and plants not readily available to animals


Nitrate toxicity

All of the commercially farmed ruminant species i.e. cattle, sheep, deer and goats are susceptible to nitrate toxicity. Nitrate is taken up by plants from the soil and is converted into protein for plant growth. Under certain growing conditions these levels can build up enough to be dangerous to grazing animals.

These conditions include drought followed by rain, cloudy weather with active growth and the addition of nitrogenous fertilizer. Plants that have been associated with nitrate problems include rape, choumoellier, turnips, ryegrass (particularly new grass and short rotation Italian types), wheat, barley, sorghum and oats. 
When animals graze plants high in nitrate, nitrite (this is not a chemistry lesson but nitrite is simply nitrate with one oxygen removed) builds up and binds to the haemoglobin in the blood. This interferes with the blood's ability to carry oxygen and turns the blood a brownish colour. Symptoms range from sudden death through to increased breathing rate, gasping, increased heart rate, incoordination and salivation.

If you are concerned that this profile fits your animals, remove them from the offending material immediately and call Tararua Vets. This is one toxicity for which we have a specific antidote: if given early, methylene blue can minimise losses.

However, prevention is better than cure! There are several management strategies that can be employed to reduce the risk of grazing potentially dangerous crops or pastures. These are essentially concerned with reducing the time grazing these paddocks, managing the amount of gut-fill prior to being introduced onto the paddock or new break, and careful observation.

If you have paddocks that you are concerned about, bring in a supermarket bag of the plant material. We can analyse the nitrate levels and give you advice on how safe this pasture is to use.


Oak and acorns

Plant description

The trees often stand alone and are up to 30m tall. They have characteristic leaves, usually 2-4 at the end of a twig. Unripe acorns are the most dangerous.

Animal species affected

All species but cattle, sheep and deer seem to seek acorns out. 

Symptoms of poisoning

Symptoms first seen 2-3 days after ingestion and for up to 5 days after removal of acorns. Depression, anorexia, constipation, rumen stasis, severe abdominal pain and acorn remnants may be seen in the faeces. Death may occur. The milk from affected animals may taste bitter. 


Call the vet. Blood tests can help determine the animal's prognosis, and symptomatic care may help those that have not ingested a large volume of acorns.



RagwortPlant description

Flat rosette of tough, dark green, irregular leaves and closely packed heads of small, yellow, daisy-like flowers present in summertime. Seeds are downy for wind distribution. 

Animal species affected 

Horses and cattle mainly. Sheep, goats, poultry and pigs can also be affected but usually to a lesser extent. 

Symptoms of poisoning

Rapid onset signs (heavily contaminated pasture) - dull, weak, colic, yellow eyes and gums, nervous signs, death Slow onset signs (chronic exposure) - loss of condition, loss of appetite, constipation, decreased milk production, depression, loss of coordination when walking, dark urine, drowsiness. 


Remove from source. Feed a highly-digestible diet with low protein, high energy. Keep in safe, flat paddocks while they are weak. Provide easy access to food and water.


Goat's Rue

Goat's Rue.jpgPlant description

This legume grows to 1.5m tall, with unequal pinnate leaves that have oval-shaped leaflets 2-5cm long. The flowers can be purple to light blue, with pods up to 5cm long. Poisoning occurs when the plant is flowering or has pods. 

Animal species affected

Cattle and sheep

Symptoms of poisoning

No signs were seen for 24 hours after eating, after which breathing difficulty develops. Death can occur if grazed on pasture rife with goat's rue. 


No effective treatment - do not graze this weed where possible



PoroporoPlant description

Soft-wooded shrub, up to 3m tall with dark green irregularly-lobed leaves. Has white to pale purple flowers and an ovoid yellow-orange berry. 

Animal species affected

Cattle and sheep

Symptoms of poisoning

Abdominal pain, vomiting, diarrheoa, weakness, inco-ordination, trembling, drooling, nasal discharge, jaundice, deep depression, difficulty breathing and cardiac failure leading to death. Ironically, the faster the toxin passes throught the body (the worse the diarrhea), the less toxin is absorbed and the better the prognosis. 


Call the vet - symptomatic treatment and drugs to minimise toxin absorption.



TutuPlant description

A native with roughly oval, dark green leaves. The tree tutu can grow up to 6m tall, with a trunk of 30cm, compared to the smaller varieties that grow up to 40cm tall. 

Animal species affected

Cattle (sometimes sheep) - usually only graze tutu when short of grass Symptoms of poisoning: 
Symptoms seen within 24-48 hours of ingestion. Drooling, nausea, excitement, convulsions, coma and death. Cattle may become aggressive, bloated and may regurgitate


Call vet - need to give medication (barbiturates) to antagonize tutin action



NgaioPlant description

Grows up to 10m tall, dark brown furrowed bark. Leaves are 4-10 cm long, sharply pointed with minute serrations above the middle half of the leaf. If held up to the light, they have distinctive glands that can be seen as clear vacuoles. Flowers are white with purple dots and are found in bunches of 2-6. The fruit is reddish-purple with an oblong kernel. 

Animal species affected

Cattle, sheep, pigs and horses

Symptoms of poisoning

Sublethal dose causes sensitivity to sunlight (photosensitivity) Lethal cases will display severe constipation; abdominal pain; small quantities of dry, blood-stained faeces; lethargy; anorexia and possibly jaundice


Symptomatic treatment of the photosensitivity An enema of raw linseed oil, soap and water



OleanderPlant description

A flowering shrub that can grow up to 3m tall. It has elongated and pointed leaves with a prominent midrib. It has large clusters of red, white or pink flowers in late spring and early summer. 

Animal species affected

All livestock, especially cattle

Symptoms of poisoning

Abdominal pain, trembling, weakness, drooling, frequent urination and bloody mucoid diarrhoea may be seen, but death can occur rapidly. 


Call the vet - aggressive decontamination required but prognosis is poor.


Wandering Jew

Wandering JewPlant description

Wandering Jew is a dark green, succulent, creeping carpet up to 50cm thick. A hairless trailing plant, it has oval, shining leaves (3-6cm) with very short stems. Wandering Jew produces clusters of small, white, three-petalled flowers from August to November. It is widely found as part of the undergrowth on the banks of rivers. 

Animal species affected

Causes allergic dermatitis in dogs and other animals walking through mats of this plant. 

Symptoms of poisoning

Red, itchy skin in areas that make contact with the plant, so commonly seen under the abdomen and in the groin area. Cases are usually seen during the summer months. 


Soothing ointments such as Aloe Vera may help, but usually, the animal will require medication to get the itch under control and to alleviate any secondary skin infections sustained due to the skin being broken while scratching.


Onion and Garlic Toxicity

The hidden dangers of onion and garlic toxicity Did you know that onions and garlic in any form (raw, cooked, dehydrated or powdered in a seasoning) can create a life-threatening form of anaemia in both dogs and cats! 

What happens in onion and garlic toxicity?

Onions and garlic contain a substance called thiosulphate which dogs and cats cannot properly digest. A build-up of thiosulphate causes a protein called haemoglobin, which is carried by red blood cells, to form clumps which in turn cause the red blood cells to rupture. When enough red blood cells are destroyed, anaemia occurs and the body is starved of oxygen. The degree of anaemia usually depends on the amount of onion/garlic eaten and some dogs and cats can develop severe reactions even after eating very little. Small amounts of onion/garlic fed over a longer period of time can create illness just as a one-time dose can. Symptoms of toxicity sometimes take several days to become apparent and can include weakness/lethargy, vomiting, diarrhoea, difficulty breathing, collapse, pale or bluish gums and/or an increased heart rate. 

How much onion or garlic is toxic?

The amount of onion/garlic (in grams) that can cause toxicity is equal to 0.5% of the animal's body weight. For example, a 10kg fox terrier needs to ingest 50 grams and symptoms may become apparent. This works out to be only a quarter of an average-sized onion. 

Treatment of onion and garlic toxicity

If ingestion was recent, making the animal vomit and giving intravenous fluids is the traditional treatment. If anaemia is severe, a lengthy hospital stay and a blood transfusion may be necessary. 

Preventing onion toxicity:

Onions and garlic are common in many human foods, including some baby foods, sandwich meats, canned spaghetti, burger patties, gravies and fast foods. Carefully check the ingredients of any table food before treating your dog or cat to a snack. Avoid adding onions in any form to homemade pet food recipes and always make sure rubbish is kept covered and away from your pets.


Nitrate poisoning

Nitrate poisoning threatens both the cow and her unborn calf. Nitrate only becomes a health risk when plant levels become extreme (>2.0 g nitrate/kg dry matter). The risk of nitrate poisoning can be managed.

Reducing risk factors

The best approach is not to feed high-risk feeds until nitrate levels decline. In reality, by following some basic principles you can minimise the risk.

Feeding risk factors

  • Don't put hungry stock on a high-risk crop. Fill them up first with hay or grass.
    • Provide a shallow break that is long across the face so all animals have access.
    • This controls the amount and rate at which feed is eaten.
    • The greatest risk is in the first few days of feeding, so introduce stock gradually over 7-10 days.
  • Plant risk factors:
    • Rapidly-growing forage and fodder crops can accumulate excess nitrate. Allow the crop to mature but feed before flowering.
    • Grazing level of plant. Nitrate levels tend to be higher in the lowest third of the stalk.
    • The first grazing of newly-sown perennial ryegrasses, short-rotation ryegrasses, forage crops, and brassica crops may be particularly dangerous.
  • Environmental risk factors that may increase plant uptake of nitrate are:
    • Drought stress.
    • Reduced photosynthesis following temperatures <12°C, plant damage (frost or disease), and cloudy days.
    • Nitrogen fertiliser, particularly if plant growth is limited by other factors, such as drought or low temperatures.
  • Ensure stock always have access to fresh, clean water.
  • MONITOR STOCK! Symptoms of nitrate poisoning will show within an hour or two of eating excess toxic feed. Look for increased salivation, pain, diarrhoea, muscle tremors, and open-mouth breathing and sudden death.
    • At first sign of any trouble, remove animals from suspect feed quickly and QUIETLY. Offer good quality hay or silage, and call the vet.

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