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As a general rule, fresh plants have a smaller concentration of therapeutic secondary metabolites than plant extracts. In the wild, an animal has the opportunity to self-medicate as soon as it starts feeling unwell and so can knock the condition on the head as soon as it arises. Captive and domestic animals do not usually have this opportunity, which means their condition can worsen to such an extent that the concentration of secondary metabolites found in the fresh plant would not be enough. For example, one of the elephants we worked with, Sinya, at the Sheldrick Wildlife Trust in Kenya, selected 5ml of undiluted garlic essential oil on some days and 2ml on others to bring her back to health from a life threatening illness. This is equivalent to 10 kilos of garlic bulbs. The lipid soluble nature of the essential oils allows them to be more easily absorbed through the membranes in the mouth, thus offering a potent application. This route of administration will mean that fewer compounds are broken down by the liver and so more compounds are able to target the problem, in garlic’s case allicin.

Plants are made up of a cocktail of chemical constituents that share many different plant species across the world, in the same way that food constituents are found in many varieties of foods. Over the course of evolution animals have evolved the ability to detect the therapeutic constituents within plants. These constituents can be produced by different species of plants throughout the world. For example linalool is the principle constituent in lavender, which is found in Europe. Linalool is also found in over 200 species of plant throughout the world including cinnamon (South East Asia) and coriander (Europe, North Africa and Asia). Another example is hyperforin, the anti-depressant molecule found in St John’s Wort (Europe). It has also been recently found in the Baikal Skullcap, a completely unrelated species of plant found in eastern Russia.

It appears that animals have evolved the innate ability to detect the required therapeutic constituents in plants rather than the plants as a whole. Since many constituents are found in plants all over the world animals are able to reliably select many foreign plants. However given the choice between a local plant and one that grows elsewhere of the same species, the choice will generally be the local plant.  For example, when I offered elephants in Kenya French peppermint they all wanted to ingest some, however when given the choice between French peppermint and Mount Kenya peppermint, they preferred the latter.

Food is usually eaten until the animal is full, plant secondary compounds (plant medicines) are selected till the taste changes from pleasant to unpleasant (sweet to bitter).   Fats, Carbohydrates and Proteins: Fats, carbohydrates and proteins (also known as primary metabolites) are used for energy production, growth and repair. An animal may select these when they are not immediately needed since they can be stored for later, allowing the animal to have an energy source when food is scarce.  

Nutrients (Barley grass, Rose hips etc): The body uses nutrients (vitamins and minerals) to assist in the production of energy, growth and repair. Vitamins and minerals cannot provide energy by themselves and so animals will not treat them as an energy source to be stored for later. So, unlike the food groups above, the animal will select these nutrients only when needed. Nutrients will be selected when there is either a deficiency or when there is a need for extensive repair to bring the body back into a healthy state. For example, vitamin C helps enzymes produce more collagen.  

Medicinal plant constituents: These would not be eaten for food. Since such constituents can be detrimental to healthy animals, the body tries to get rid of them rather than storing or regulating them; using detoxification enzymes to break them down into products that can be easily removed from the body. Secondary compounds affect the body in ways other than energy production, growth and repair. As a general rule they affect how cells communicate with each other (e.g. how nerve cells talk to each other and how messages are sent from the cells surface to the DNA).  

Essential oils and absolutes would be considered medicinal plant constituents as they do not contribute to energy production, growth or repair.  Macerates & Dried Herbs may have some nutritious compounds (e.g. the fatty oil in macerates). However, the presence of medicinal plant constituents would still deter healthy animals from using them for food.  Nutritional Powders and rosehips have high concentrations of vitamins and minerals so would be put nearer the nutrient end. However, animals would treat these as a supplement rather than as a staple food as they still have little energetic value. 

It is an unfortunate fact that animals sometimes poison themselves. In many instances this is due to consumption of artificial compounds but occasionally plants can be the causative agent. New Forest ponies sometimes succumb to acorn poisoning, domestic horses have been known to fall ill after chronic ragwort consumption and there have reports of dogs poisoning themselves on grapes. This is hard to reconcile with the observations that animals can accurately select the plants needed to rectify any problem they are experiencing. So if the ability to self-medicate is innate why would an animal select something that is bad for them?    

1) Hunger: If food is scarce animals may have no option but to start foraging on toxic plants it would not normally eat. This may happen to animals who only have access to poor pastures; if there is nothing good to eat but ragwort, you will have to eat ragwort as it has at least some sustenance. This may also explain why ragwort is more toxic when it is taken systematically over a significant period of time. As a wild animal can wander, it may only have to supplement its diet with ragwort for a short period of time before it finds more nutritious food.  

2) Inability to sequentially select: Several species have been seen to ingest neutralizing compounds after eating plants with high levels of plant toxins. Clay can neutralize most plant toxins whilst saponins (such as though found in Slippery Elm & Marigold) can neutralize tannins (acorn poisoning occurs due to their high tannin content). Captive animals often do not have access to neutralizing compounds and so will not be able to sequentially select.  

3) Artificial context: For example it is well known that chocolate can poison dogs. This is due to its theobromine content, an alkaloid found in the coca plant that dogs cannot metabolize very well but that humans can. Chocolate also contains other ingredients, most notably sugar and flavourings such as vanilla. It may be that the additional ingredients in chocolate mask the smell and taste of the theobromine, preventing the dog from perceiving it as distasteful (just as adding sugar to other medicines makes them more palatable). Anti-freeze would also come under this category, since dogs do not have the detection mechanisms in place for artificial chemicals that taste applealing.  

4) Grapes are considered toxic to dogs though it is important to note that the first reported case of grape poisoning in dogs was in 1998. The Veterinary Medicine Association suggests that grapes and raisins can be toxic and fatal to dogs in rare instances; however, it is unclear as to whether the whole grape can be toxic or if it is just the flesh and skin (and not the seed oil). The Ingraham Academy have had no known instances of poisoning with grape seed oil, which dogs often select with relish and to great effect, however it is a subject that needs further investigation.

Sarah Kinson a graduate of the Ingraham Academy, who works with captive meerkats, recently offered them powdered green clay to see their reaction to it; initially they scratched around in the clay and rolled in it. However, she then noticed some of the meerkats taking their food, dusting it and rolling it in the clay before eating it. On further observation, she realized that the only food being taken to the clay was the grapes. The only other food she had seen them roll in the clay was a chick; they are fed dead day old chicks as part of their diet, however she did not see this happen again, only the grapes.  

Another student had a dog that had a seizer due to eating grapes, however when she read that dogs often select the oil with positive effects she decided to offer the grape seed oil, which her dog continued to take with no ill effect. This made me consider the possibility of if the culprit is mycotoxin (a fungal toxin) found on the skin of some grapes, especially as another student noticed his parrot pealing the skin off some grapes but not others.  

As green clay is a well -known detoxifier, this could be why they are utilizing it in this way. lso considered toxic to dogs though it is important to note that the first reported case of grape poisoning in dogs was in 1998.   

It is important to note that very few plant constituents are inherently toxic. A plant secondary metabolite may be detrimental when not needed but can confer health benefits when it is needed (when the correct concentration has been self-administered). For example, we witnessed a young puppy who, instead of eating his food, chose to eat an onion. Onions are normally considered toxic to dogs but not only did the puppy show no ill effects, he also purged a large quantity of tapeworm segments shortly afterwards and then had no further interest in the onion.  

In the 25 years since we enabled the first animal to self-medicate there have been no reported cases of an animal poisoning itself.  

N. B. When working with horses, always have a bottle of seaweed, German chamomile and peppermint to hand. Horses are very vulnerable to colic and there are many circumstances that can act as a trigger. For example, horses can get colic from consuming too much of something too quickly. Considering that domesticated animals tend to be deprived from plant secondary metabolites, when some become available they may want to ingest large quantities in a short space of time, which might theoretically induce colic. Peppermint, German chamomile and seaweed are oils that horses with colic select.  

If an animal does show the effects of tannin poisoning e.g. acorn poisoning in horses, try offering extracts rich in saponins such calendula/marigold and slippery elm or clay whilst waiting for the vet. Clay is good one to offer with other poisonings.

Your dog may select remedies to purge toxins, this is a natural dog behaviour and signs of improved from the original condition should be seen within 24 hours. If the toxins are in the hind gut then this will be seen as loose stools or diarrhoea.

here are several websites that make statements along the lines of “There is a lot of information out there on essential oil toxicity in cats.” Unfortunately, these websites do not cite their sources (which is a reliable indicator of an unsubstantiated claim). The fact is there is hardly any information out there on essential oil toxicity in cats. Do not trust any website that makes claims without citing its sources.

An extensive publication search brings up just three reports on essential oil toxicity to cats; two involved the use of tea tree (1,2), the third with potpourri (3).  

There are no reports on the toxicity of other essential oils with cats and not even a mention in two popular veterinary toxicology (4,5). There are plenty of mentions of toxic household plants but none of these feature in the applied zoopharmacognocist’s kit.

The concern with cats over other species is more theoretical than actual. The issue is that cats have very low glucuronyl transferase activity, an enzyme involved with breaking down some foreign chemicals including alcohols and, more importantly, phenols (3). There are only a small number of essential oils that contain significant levels of phenols, the most commonly used being clove, cinnamon, wintergreen, yellow birch and the phenol rich chemotypes of thyme. In our experience and the experience of our students, it is incredibly rare for a cat to select any of these oils, and in the odd case where there has been a selection it has almost exclusively been through inhalation.

Almost invariably cats will select essential oils through inhalation and will almost never select them orally (the form of administration cited in the above papers are either topical or unknown). Some websites claim that allowing cats to inhale is also risky; again there is no evidence to suggest there is a risk, especially if the oil is offered in well ventilated areas and the cat is free to remove itself from the odour.

 

References 

1 Bischoff (1998). Australian tea tree (Melaleuca alternifolia) oil poisoning in three purebred cats. Journal of Veterinary Diagnostic Investigation

2 Villard D, Knight MJ, Hansen SR et al (1994). Toxicity of Melaleuca oil and related essential oils applied topically on dogs and cats. Veterinary & Human Toxicology 36: 139-142. 

3 Schildt Julie C.; Jutkowitz L. Ari; Beal Matthew W (2008). Potpourri Oil Toxicity in Cats (2000-2007)  Journal of Veterinary Emergency and Critical Care 18: 515-516

4 Peterson ME & Talcott P (2007). Small Animal Toxicology. Elselvier Inc.

5 Campbell A, Chapman M (2000). The Handbook of Poisoning in Dogs and Cats. Gray Publishing.