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Plant toxicity

Buttercups are on many lists of poisonous plants. They contain an irritant that can cause dermatitis in humans that handle buttercups and salivation, oral ulceration and gastrointestinal irritation in animals that eat them. Buttercups have a bitter taste and are not a problem for rabbits. They can eat small, young leaves that are growing in pastureland without ill effects. The mature leaves, tall plants and flowers unpalatable to rabbits so they do not eat them.

Plant toxicity is a cause of anxiety to rabbit owners and there are many sources of information that will add to their concerns. It would easy if plants could be classified as ‘poisonous’ or ‘non-poisonous. Unfortunately, this is not the case, which is why there are long lists of plants that ‘could be poisonous’ that are unnecessarily alarming to rabbit owners. In reality, rabbits are very difficult to poison with plants. History has proven this to be the case. Unfortunately, long lists of poisonous plants are so disturbing for owners that they frighten them into buying commercial foods instead, which are more likely to cause long term health problems, such as obesity and dental disease, than fresh plants. This risk of poisonous plants can prevent owners picking plants for their pet or allowing the rabbit to have access to a garden. This is a shame because a diet of fresh plants and is enjoyable for the rabbit and has many health benefits. Wild plants also cost nothing, which may be important for owners with many rabbits to feed. Some lists even include vegetables, which is illogical as we feed ourselves and our children on them. Chemical that are sprayed on to vegetables are more likely to be a problem than the vegetables themselves

What is meant by 'poisonous'?

The word poisonous is emotive. It can make owners believe that if their rabbit has even a small mouthful of a plant on the poisonous plant lists, it will die. This is not the case.   Some lists of poisonous plants use the term ‘poisonous’ interchangeably with 'toxic', ‘hazardous’ or 'dangerous'. This difference may seem trivial but it allows plants, such as nettles, buttercups or clematis that cause a skin reaction in humans to be included in lists of plants to avoid. Giant hogweed is another example. This plant is a hazard to the human that picks it because it causes a serious, blistering skin reaction and can result in phototoxicity. Its effects in rabbits are not known. Any plant with thorns is also considered to be hazardous, which is not the same as poisonous.

What makes a plant poisonous

These leaves of the foxglove (Digitalis purpurea)  have been nibbled by a young wild rabbit. It is not unusual for them to taste plants and not try them again. The plant and the rabbit survived.Plants are poisonous if they contain a toxic compound (e.g alkaloids or glycosides)  that could harm an animal that ingests that plant. These compounds may irritate the digestive tract causing nausea, vomitting and diarrhoea in some species. Other toxic principles affect the nervous system causing convulsions and other neurological signs. The amount of the toxic compound is variable in the parts of the plant. Sometimes only parts of the plant contain the toxic priciple. For example, the leaves of the yew tree (Taxus baccata) are extremely poisoning and can cause sudden death in livestock that eat them but the fleshy part of the berries are non toxic. Birds may eat them. Even some humans eat them but this is not recommended. Another example is rhubarb where the stems are not poisonous but the leaves might be. The poisonous content of a plant may change from early growth to maturity. Some plants, are more toxic in advanced stages of growth, whereas others are more poisonous when they are young. In some cases, drying may increase or decrease the potential of a plant to be poisonous.  

The amount of a toxic compound that an animal ingests affects the ability of that compound to be harmful so if a rabbit nibbles the edge of a leaf it will only consume a small dose of a potentially poisonous plant. At the other end of the scale, if a rabbit only eats one type of plant or vegetable and little else, it could receive a high enough dose of a toxic compound. A theoretical example is cabbage, which contains a goitregenic compound that inhibits iodine absorption.                       

Rabbit's resistance to toxic compounds in plants 

Rabbits are resistant to some of the toxic compounds in poisonous plants. For example, rabbits are resistant to pyrrolizidine alkaloids that are the toxic principle of several plants including common ragwort (Senecio jacobea) (http://pubs.aic.ca/doi/abs/10.4141/cjas84-224) and some rabbits are resistant to the toxic effects of deadly nightshade because have high levels of plasma atropinesterase that breaks down atropine.  http://www.ncbi.nlm.nih.gov/pubmed/16736160. Atropine is the toxic principle of deadly nightshade.

Apple pips 

Many websites say that apple seeds are toxic to rabbits because they contain cyanide.  Although, it is true that apple seeds contain a small amount of cyanide, the toxin is protected by the hard seed coating so it passes straight through the digestive system of most animals. Although there is a possibility that a rabbit might chew the seeds so the contents would be released into the gut, the cyanide is present in such small quantities that it can be detoxified by the body. The rabbit would have to eat a large amount of apple pips to suffer any ill effect. There are no reported cases of a rabbit dying from eating apple pips. In the autumn, wild rabbits feast on windfalls, including the pips, with no ill effects.

Deliberate attempts to poison rabbits

Domesticated pet rabbits are descended from wild rabbits that originated in Spain and Portugal and were introduced to many parts of the world (including the UK) to provide meat, fur and sport for voyagers and settlers. Some of the introduced rabbits either escaped or were released into the wild where they bred successfully to become a pest species that destroyed the natural habitat and changed the landscape and ecology dramatically.  Australia is a good example of a location where this has taken place. In some states, drastic control measures have been deployed to control rabbits, including building a fence 2000 miles long and dropping poison in baited food, such as apples or carrots, from helicopters and aeroplanes. The cost has been enormous and illustrates how difficult it is to kill rabbits. Growing a palatable, poisonous plant that rabbits would eat would be a much easier and cheaper solution. Such a plant doesn’t exist. For example, buttercups and apples pips are on many lists of poisonous plants for rabbits. These would definitely have been used if they killed rabbits easily. They don't. 

Rabbit resistant plants

Any gardener who has wild rabbits eating their herbaceous border or entering their vegetable plot knows that rabbits will eat a wide variety of plants. As a result, there are many lists of rabbit resistant plants that gardeners can grow because rabbits will not eat them. An example is on the Royal Horticultural Society website  https://www.rhs.org.uk/Advice/Profile?PID=209. If this list is cross referenced with lists of poisonous plants, it can be seen that rabbits do not eat the poisonous varieties.  The list of poisonous plants is the same as the rabbit resistant plants.

When rabbits have no choice..

Although it is difficult to poison rabbits with plants, it is not impossible. There are experiments where laboratory rabbits have been forced to eat a poisonous plant or plant extract, either because they have no choice or because it has been ground up and incorporated into the pellets that they are fed on. The results of these experiments have shown that rabbits can be ill or die after ingestion of plant poisons. This is not a natural situation because there is usually a choice of plants for a rabbit to eat but it could be mimicked in a house where there are ornamental houseplants and no other vegetation for a rabbit to eat. As a general rule, houseplants and rabbits are a bad combination. Not only is there a risk of poisoning the rabbit but there is the likelihood of damage or destruction of the houseplant.

Reports to Veterinary Poisons Information Service (VPIS)

Although, I have never seen a confirmed case of plant poisoning in a rabbit, I know it can happen. The Veterinary Poisons Information Service (VPIS) http://vpisglobal.com/ collects data (including the outcome) on cases of poisoned animals that are reported to them by vets in practice. They have had some rabbit cases (Nicola Bates, personal communication). The number is small i.e. less than 1% of their enquiries. Most of their enquiries have been due to houseplants such as lilies, ivy, chrysanthemums, aloe vera and poinsettia. Some rabbits showed no ill effects, while other showed signs of disease.  Lethargy, diarrhoea, abdominal tenderness, nystagmus, muscle fasciculation, paralysis, coma, collapse, hypothermia were seen in some rabbits that had eaten ivy. These rabbits either recovered or died.  Rabbits that ingested poinsettia, lilies, swiss cheeseplant (Monstera deliciosa), weeping fig (Ficus benjamina) were generally asymptomatic (no signs of disease). Fatalities were reported in a rabbit that had ingested an umbrella plant (Scheflerra species) and another that had eaten a rubber plant (Ficus elastica). Some rabbits were unwell after eating azaleas. One died suddenly. Ingestion of potentially poisonous garden plants also showed a variety of outcomes. Most rabbits that ate foxglove or rhubarb leaves remained asymptomatic whereas two that ate laburnum (Laburnum anagyroides) died. There was one reported fatality after ingestion ivy (Hedera) and another of willow (Salix sp).  It is known that rabbits can eat both these plants with no ill effect although ivy is not a plants that should be picked for rabbits. Willow is a plant that is considered safe for rabbits and many pet rabbits are offered it. This fatality (and maybe the others) could have been due to another cause. Without a post-mortem examination, the cause of death cannot be certain.

Picking wild plants 

While reports of rabbit deaths following ingestion of poisoning are disturbing, they are rare and should not put owners off allowing their rabbits to graze in the garden or to pick plants for them. The VPIS reported no incidents of toxicity associated with wild plants although, in the literature, there is a case of rabbits dying after being given hemlock in mistake for carrot tops (Short B, Edwards C. 1989 Accidental Conium maculatum poisoning in the rabbit. Vet Hum Toxicol 31:54–57). Hemlock is a rare plant and usually found in damp marshy areas. My advice to owners that have access to weeds, herbs and plants in their gardens, on verges or next to footpaths is to choose 5-6 varieties that they recognise and know their rabbit will enjoy. They can pick these in the knowledge that they are safe. See section on 'Free food for rabbits' It is wise to avoid plants that are known to be toxic. 

 My own experiences

This is a picture of my garden in 2004 when rabbits had free range. Now it is occupied by guinea pigs. The netting in the background was put there to protect the ivy that grows over the wall. The rabbits had started to chew the stems. The snowdrops come up each year and the rabbits (and now the guinea pigs) leave them alone until the leaves die back when they eat them with no ill effect.

As a vet who specialised in treating pet rabbits, I have never seen a case of plant toxicity. I have performed post-mortem’ examinations on many rabbits that have died unexpectedly and have never diagnosed plant poisoning. There are many, many other reasons why rabbits can become ill and die suddenly.  I have kept rabbits in the garden and my conservatory for the last 20 years without ill effect. When the rabbits were first introduced to the garden, they ate most of my annuals and some of the perennials. Nowadays, the mainstay of their diet is grass, vegetables, plants and herbs picked from the field, garden and verges. They have access to hay that they may or may not eat. Outside, my rabbits have had free access to fallen apples, rhubarb, ivy, snowdrops and daffodils without ill effect. The picture on the left shows part of my garden in 2004. The netting in the background was put there to protect the ivy that grows over the wall. The rabbits had started to destroy it by chewing the stems. The snowdrops come up each year and the rabbits leave them alone until the leaves die back when they eat them with no ill effect.

Some of my rabbits live in the conservatory. They differ in their efforts to eat the plants but over the years, the rabbits that have lived in there have destroyed my cheeseplant, ring-barked citrus trees and consumed or nibbled other houseplants. Some plants e.g philodendron ( a plant that is listed as dangerous ) and clivia don't seem to tempt them. Now the conservatory has been adapted so the rabbits can't reach the plants but this is to protect the plants rather than the rabbits.