Domestic cats eat grass to purge parasitic worms from their gut

There has been a long discussion on the internet about the reasons why domestic cats eat grass. Many years go, Dr Desmond Morris suggested that domestic cats ate grass to ingest folic acid in the grass to aid in digestion. A study carried out at the University of California, Davis, School of Veterinary Medicine: Characterization of plant eating in cats, came to a different conclusion. The study refers to ‘plant eating’. My interpretation of the word ‘plant’ typically means ‘grass’ although cats do like to eat other plants sometimes which is why warnings are issued about plants which are toxic to cats.

Cat eating grass

In short, the study concluded that regular plant eating was a standard feature of the behaviour of the domestic cat’s wild ancestors and the behaviour has been inherited by domestic cats.

There are numerous reports of wild carnivores eating plants. Studies on primates reveal that eating digestible plants purges the intestines of parasitic worms. This is to be expected because the study concludes that all wild carnivores carry an intestinal parasite load. Therefore, regular instinctive plant eating is a way of “maintaining a tolerable intestinal parasite load, whether or not the animal senses the parasites”.

There you have it: grass eating helps clear the intestines of parasitic worms such as tapeworms and roundworms (helminthic parasites) according to these scientists.

Some facts about the study

The study was web based and the participants had to observe their cat’s behaviour for 3 or more hours a day. They reported that 71% of the cats had been seen eating plants at least six times. 11% of participants said that their cat never ate plants. 61% said that they ate plants more than 10 times. Of these cats 67% were estimated to eat plants daily or weekly. The participants said that their cat always appeared normal beforehand. 27% said that their cat often vomited after eating plants. This lowish percentage indicates that the reason for eating plants was not to vomit.

It appears that young cats of 3 years of age or less engaged in more plant eating compared to older cats of 4 years of age or older. 39% of the younger cats ate plants while 27% of the older cats ate plants.

A higher percentage of older cat vomited after eating grass. The researchers did not conclude that cats ate grass to vomit because they felt ill. They also said that dogs behaved in a similar way in respect to grass eating. The researchers also stated that they did not believe the hypothesis that young animals learn plant eating from older ones.

Researchers: Benjamin L. Hart, Lynette A. Hart and Abigail P. Thigpen – University of California, Davis, School of Veterinary Medicine, 1 Shelds Ave, Davis, CA 95616, USA.

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