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Grass Eating: Why Dogs and Cats Go for the Greens


"Why does my dog or cat eat grass?" Pet owners often ask this question, and are surprised to find that there is no clear answer. It's a mystery even to veterinarians and researchers. This is especially puzzling for owners of the carnivorous cat. Most dog and cat owners report that their pets eat grass or other plant material on a daily or weekly basis, and some report that the pet vomits afterward. There is a common belief that pets eat grass because they are ill and need to vomit.


This hypothesis does not hold true, according to a recent web-based survey of 3,000 pet owners. Only a small percentage of pet owners reported signs of illness before or after their pets ate grass. In fact, less than one in four reported that their pets vomited afterward. Younger dogs were more likely to eat grass than older dogs, and were more likely to get sick afterward. But, grass-eating does appear to be a normal behavior unrelated to illness.


Another hypothesis is that eating grass provides nutritional value the pet is not getting in its daily diet. Pet owners who serve their dogs and cats specialized diets and those who serve table scraps or non-prescription dry or canned foods all reported grass-eating behavior. Nutritional deficiency does not appear to be a reason that pets eat grass. There is no evidence that pets that eat less fiber are prone to eating plants, either.


Veterinarians now believe that grass-eating is a normal behavior unrelated to illness or nutritional deficiency. It is more likely an instinctual activity passed down from dog and cat ancestors in the wild that suffered far more than today's pets with intestinal parasites. Eating grass and plant material helps to purge the animals' intestinal tracts. The theory is that the plant material passes through the intestinal tract and wraps around worms (nematodes), thus expelling them in the feces. The reason younger animals eat less grass is that they are less immune to parasites.


The conclusion is that more study is needed, but it is likely that grass-eating is perfectly normal and typical in healthy pets. If the pet exhibits signs of illness before or after eating grass and vomiting persists, a medical exam is in order. Otherwise, if pets run outside and put their noses in the lawn, they are simply exhibiting instinctual behavior passed down from wild ancestors. So, let them eat grass.