The question is very positive in that it is asking if it is healthy and useful for a cat to eat grass. It is not asking whether it is acceptable to allow a cat to eat grass. The answer can be found in the cat’s behaviour. If a domestic cat is allowed outside into a backyard where there is grass it is quite possible that they will eat a small quantity of it. They will do this voluntarily.
A domestic cat wouldn’t eat grass voluntarily unless it serves some purpose. This must be a behaviour inherited from the domestic cat’s wild ancestor. In the wild, wild cat species frequently eat some sort of vegetation. They do this when they eat the insides of the stomach of the prey animal that they have killed. Some wild cats such as the snow leopard specifically and deliberately eat certain plants. Plants are part of a wild cat’s diet if you like. Although, it’s in very small quantities relative to the flesh upon which they are reliant as strict carnivores.
So what benefit is the domestic cat seeking when they eat grass? There are a lot of theories, from making themselves sick to remove hairballs or to eat roughage to improve digestion. However, the best answer – and I have mentioned this before on more than one occasion – is provided by Dr Desmond Morris. He argues cogently that grass contains folic acid, a vitamin that is vital to domestic cats because it plays a role in the production of haemoglobin.
This essential chemical substance is missing, he says, from a modern, purely meat diet. Cats are driven to search for it to complete their diet. Dr Desmond Morris argues that if a cat is deficient in folic acid their growth suffers and they may become anaemic. He claims that this can be a major problem for indoor cats with no access to a garden. He suggests that owners of indoor cat should provide their cats with a small tray of grasses inside the home for their cats to chew on when the mood takes them.
There is one big caveat which I’m sure you are aware of. Not infrequently people treat their lawns and back gardens with weedkillers and chemicals to enhance the appearance of their lawn. These chemicals will nearly always be poisonous to a cat. They should not be used by cat owners who let their cats go into the garden (‘backyard’ in America).
An alternative theory comes from researchers presenting their argument at the annual convention of the International Society for Applied Ethology in Bergen, Norway. Based on primate behavior they say that eating grass helps animals ‘expel intestinal parasites’ by increasing muscle activity in the digestive tract. I find this argument less credible.
Either way, to recap, eating grass is good for your cat. Don’t worry about it and even encourage it if he or she is a full-time indoor cat. But expect them to sometimes sick it up! Why do they do this if it is beneficial? I think it is because some grasses irritate the stomach. If a domestic cat ingested grass from the stomach contents of a small mammal they wouldn’t vomit it up. Eating grass is a second best process.
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