Dog eats Grass and Monkey Business

It’s not just humans that use plants as medicine. Zoopharmacognosy - the study of animal plant self-medication is a fascinating field and I thought I’d share a few examples...

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People often ask me how I think humans developed herbal medicines? Was it trial and error? Knowledge handed down the generations? Or did we learn from animals? Or even the plants themselves? The truth embraces aspects of all of these. We too are also animals and there is an inherent instinctive use of plant medicines in a wide range of animal species. There is also evidence that some medicinal knowledge is taught - especially among the apes.

Most dog and cat owners will tell you that their pet occasionally eats grass but the whole field of animal herbal self-medication is far broader and more interesting than just the ‘dog eats grass’ scenario. When I told a friend of mine that I was writing this article, she started to tell me about an old dog of hers that had had a cancerous tumour.

“Even when he was on his last legs and could barely walk,” my friend told me, “he would still go out and try to eat…”

“Cleavers?” I interrupted.

She look surprised. “How did you guess?”

“Because cleavers is well-known for its traditional use in treating cancerous cysts” I replied.

Galium_aparine

One of the best sources of information on what sick animals chose to eat, is not actually scientific journals - although I have quoted from some below. There was an amazing English veterinary and herbalist called Juliette de Baïracli Levy (1912 – 2009) who lived for many years among the Romani gypsies of Western Europe, recording their veterinary use of herbs - much of it learned from observing what the animals chose to eat themselves.

Of the 24 books that she published, the two that are best known are Herbal Handbook For Farm and Stable (1952) and The Complete Herbal Handbook for the Dog and Cat (1971). These classics are as relevant today as they were then. Zoopharmacognosy - the study of animal plant self-medication - is an expression coined as recently as 1987, so it is still a relatively new branch of science despite our association with animals over millennia!

Apes, being so like us, have always been particularly fascinating. They choose specific medicinal plants - that they’d never eat as food - to rid themselves of intestinal parasites. They fold the leaves carefully and swallow them virtually whole. Whether this is to provide coarse roughage to scrape and dislodge the offending worms, or to avoid the bitter taste, we don’t know. However, Aspilia leaf - a favourite medicine of chimpanzees - contains thiarubrin-A, known to be antibacterial. antifungal and a killer of intestinal worms. Mahale chimpanzees infected by parasites will eat the bitter pith of Vero commonia amygdalina fruit. These fruits contain an anti-parasitic compound called vernonioside.

I only recently learned that a baby orangutan stays with its mother for 8 years as it needs time to learn 300 species of edible plants and a range of other skills.

(Coincidentally, in studies of indigenous peoples most human children can identify at least 300 species by the age of 6.)

What is even more fascinating is that some animal medicine is quite sophisticated. For example, some apes use plants to control their fertility, consuming some species to enhance their fertility but other plants to prevent conception! Female woolly spider monkeys in Brazil also add plants to their diet to increase or decrease their fertility. They are very aware of which species to choose depending on whether they wish to become pregnant or when they don’t. Choosing a plant high in phytoestrogens will raise their own oestrogen level, simulating pregnancy, acting as a type of contraceptive pill. They do this when there are already small youngsters that still need feeding or parenting, to control numbers.

I have also heard of some monkeys using contraceptive plants to deliberately thwart pregnancy. When a new alpha male takes over a troupe of monkeys, they will often kill the existing monkey babies. The aim of this appears to to be to encourage the females into oestrus to sire the new male’s own offspring. The females seem to feed on contraceptive plants to deliberately avoid pregnancy - almost as an act of revenge!

Pregnant lemurs in Madagascar nibble on tamarind and fig leaves and bark to aid in milk production, kill parasites, and increase the chances of a successful birth. Females elephants, in the late stages of pregnancy, will often travel out of their way to consume the leaves and bark of a tree in the Boraginaceae family that they eat at no other time. This is the same plant that Kikuyu women brew as a tea to help labour go smoothly.

Here are some more areas where animals self-select medicines:

Wound-healing: Apes will pack plants and earth into exposed wounds as a dressing. Some lizards are believed to respond to a bite by a venomous snake by eating a certain root to counter the venom.

Insecticides: Plants are used by both animals and birds to repel and control insects. Bears, for example, will chew osha root (Ligusticum porteri) then smear it all over their fur to relieve them from insects and their bites. Osha may contain as many as 105 plant insecticide compounds! The white nosed coatis of Panama also smear an insect-repelling resin into their coats.

Detox: Some animals and birds, including red and black macaws, will even eat clay or earth - known as geophagy - as a form of intestinal parasite detox. Humans sometimes do this too, consuming fuller’s earth or activated charcoal, for example. Baboons in Ethiopia eat the leaves of a plant to combat the flatworms that cause schistosomiasis. Insects are also in on plant medicine. Fruit flies lay eggs in plants containing high ethanol levels when they detect parasitoid wasps, as a way of protecting their offspring.

Vermifuges: When it comes to getting rid of parasites, animals and birds often turn to mud, clay and minerals. Birds with mites infecting their skin will take dust baths. They’re not the only ones. Mud and dust baths are popular for flea, tick and other parasite removal by pigs, wild boar, buffalo, peccaries, anteaters, rhinos and elephants.

Mood-altering: Some South African baboons have got into the daily habit of taking a small dose of leaves from plants well-known for their stimulant property!

Antibacterial: A little closer to home, bees in the spring collect resin off sticky tree buds and use it to make propolis. When they are given free choice and access, they will choose the buds of black poplar over and above all other species, and the sticky buds of horse chestnut are the least popular. Guess what? When analysed, the black poplar buds have the strongest antibiotic properties while horse chestnut has the weakest.

These are just a few of many examples. I am sure that we humans also once shared an innate ability to detect the therapeutic constituents in plants. We have just lost our sensitivity for taste and our ability to interpret the universal meanings of chemical communication - it is after all a type of universal ‘Esperanto’, a signalling language that I call biosemiosis. One example everyone will still be familiar with though is the taste of tannin. It’s that drying and puckering of the mouth when you’ve drunk too many cups of tea. If a plant tastes of tannins it will have that drying and toning effect on your body’s tissues. Hence why blackberry leaf will dry up and stop dysentery in the gut, or raspberry leaf will dry up and disinfect pus and a sore throat. Once we knew these things.

However, I’ve yet to answer the burning question. If your dog or cat is eating grass it is likely to cause either retching or diarrhoea. This puzzling behaviour may be an attempt to self-medicate against bacteria if it’s eaten something that’s infected by vomiting it up, or it may be to rid itself of an overload of worms or parasites from the gut via the bowels. Either way, take note! Dogs cannot digest grass. They don’t produce the enzymes needed to break down grass fibres. So the trigger for eating grass may be a feeling of nausea. Dogs may have learnt this helps to sooth stomach irritation.

References

Álvaro, M. M., Luis, R. R., de Lollano, S., & Joaquin, P. (2019). The origins of zoopharmacognosy: how humans learned about self-medication from animals. IJAR, 5(5), 73-79.

Costa-Neto, E. M. (2012). Zoopharmacognosy, the self-medication behavior of animals. Interfaces Científicas-Saúde e Ambiente, 1(1), 61-72.

Isidorov, V. A., Bakier, S., Pirożnikow, E., Zambrzycka, M., & Swiecicka, I. (2016). Selective behaviour of honeybees in acquiring European propolis plant precursors. Journal of chemical ecology, 42(6), 475-485.

Mamillapalli, V. A., Jujjavarapu, B. E., & Kantamneni, P. A. (2016). Zoo pharmacognosy: Animal self-medication. Journal of Critical Reviews, 3(3), 13-17.

Plotkin, M. J. (2000). Medicine quest: in search of nature's healing secrets (pp. 48-57). New York: Viking.

Shurkin J. (2014). News feature: Animals that self-medicate. Proceedings of the National Academy of Sciences of the United States of America, 111(49), 17339–17341. doi.org/10.1073/pnas.1419966111

Cleavers Image Source: Hugo,arg. upload.wikimedia.org/wikipedia/commons/thumb/2/22/Galium_aparine001.JPG/1024px-Galium_aparine001.JPG