If you peruse the internet looking for answers to why cats eat grass, and whether they even should, you will likely not find the 'real answer'. That may be because there just isn't one. There are far more websites selling grass and promoting the eating of grass by your pet cats, than sites that objectively explain why your cat eats grass or if it is really a good thing or not. As a veterinarian, this is a question I am asked regularly, and although I certainly have an opinion about cats eating grass, I cannot cite any references or studies that back me up. (I am not saying there are none; I just don't know of their existence.) The following is a brief discussion of the pros and cons of grass-eating by cats.
There actually is a plant called cat grass: Avena sativa, or the common oat. However this name is not in common use in the non-cat world, and a Google search of Avena sativa will take a long time before you come up with an entry that includes the common name ‘Cat Grass'. Few discussions of this plant on the internet discuss its use in cat nutrition. You have to Google ‘Cat Grass' to find any discussion of cats eating grass. And in these websites ‘cat grass' really includes a large number of young grass species, from flax and barley to several varieties of wheat. So the common oat is not the only ‘cat grass'. Even catnip (Nepeta cataria) is often included in the ‘cat grass' categories though catnip is not a grass at all. This plant will be discussed in a future article, though.
A typical cat grass ad showing young Avena satira (photo by CurtisJones)
Though no one can deny that cats eat grass, there are only theories as to why they do. Some claim it is to get extra niacin, a B vitamin abundantly available in most fresh young grain grasses. Perhaps cats eat it to make themselves vomit. Some people believe cats eat it to help pass fur balls along while others say they just need the fiber for other nutritional purposes. And some say cats eat grass because the like it or like to ‘try' things. Which theory is correct, or are any of them right?
Whether or not cats extract any nutritional products from grass ingestion is not clear and I cannot find any scientific studies that support this claim, though it might happen. Whether or not it does, it is highly unlikely cats eat grass for this purpose, as few cats are truly deficient in any B vitamins (unless they are being fed an improper homemade diet or are starving.) If a cat ate grass for this reason, I assume it would be an instinctual behavior. Then why do some cats not eat grass even if it is offered to them? Evolutionarily, cats eat a lot of vegetation incidentally when they consume the stomachs and intestines of their prey. But it is very difficult to determine whether this incidental ingestion is an essential part of their nutrition. Either way, it is highly unlikely that catgrass supplies a necessary ingredient that a cat does not get from some other common food source.
Do cats need fiber? Even the answer to that simple question is not terribly clear, but it is likely they do. However it seems unlikely that cats need much, if any, plant fiber. Cats eat meat, and there is some fiber in red meat, but some people claim that isn't enough fiber. Many cat foods include plant fiber, and some veterinary diets even include excess plant fiber as it seems to help with some digestive and other metabolic problems that cats can develop. But new research is now showing that perhaps other dietary changes are equally effective, if not superior, in treating these metabolic problems. Nothing so far shows that cats need plant fiber, at least not in the form of edible grass. However, there is no research that shows plant fiber, consumed in moderation, is bad for cats, either.
What about fur balls? Cats do ingest quite a bit of fur and some will vomit up fur balls now and then, while other will vomit them up frequently. Eating cat grass may indeed help some cats pass fur through their digestive tracts more easily. But from an evolutionary standpoint,vomiting up fur balls frequently is not likely to be a ‘natural' process. Lions and tigers do vomit up fur occasionally, but not very commonly. Modern domestic cats have been bred to grow all sorts of ‘unnatural coats' that include very long and/or very fine hairs and these hairs may cause more digestive problems than nature has been able to deal with. So we may have created, through selective breeding and gene manipulation, populations of cats that have more trouble with hair ingestion and processing than do wild cats. Maybe these modern creations do need some added fiber to help take care of their unnatural hair burdens. Most feline veterinary specialists think that cats that vomit up hairballs frequently (more than one to two times a month) probably have something wrong with their digestive tracts; relying on cat grass to treat their vomiting problems is ignoring potentially more serious illnesses. Either way, this still does not answer the question of whether eating the grass is good for cats, or if this is why cats eat grass in the first place. The first answer is unknown but the second answer is probably no.
Tiger vomiting up after eating grass
Do cats eat grass to make themselves vomit on purpose? This is also unlikely in most cases, but I cannot say for sure this is never the case. Many dogs will eat grass when their stomachs are bothering them and these dogs seem to eat grass purposefully (though perhaps not truly knowing why they are doing it) to make themselves vomit. However it is obvious that many dogs will eat grass almost anytime they get the opportunity and it seems they just like to do so. Vomiting then is the unintended result. And this is probably the case with almost all cat-vomiting post cat grass ingestion. Cats just seem to like eating grass. Perhaps it's the sweet flavor, the crunch or some yet unknown attraction. Why they vomit from eating grass is known, however. Grass is indigestible and also has rough edges (some more than others). This combination irritates the gastric mucosa and the result is vomiting. By the way, mature grass has awns which can not only be extremely irritating, but can ‘bore' holes into the GI tract and even sometimes penetrate it completely. For this reason it is not a good idea to let your cat eat grass with awns on it (mature Avena sativa will develop awns, also known as oats.)
Mature awns (oats) of Avena satira (photo by kennedyh)
Though I can't say for certain that eating cat grass is healthful, I can at least say that it is probably safe in most cases. Offering grass to a cat, particularly an indoor cat, can distract them from nibbling on other, potentially hazardous and toxic indoor houseplants and other items. It is far better for a cat to eat immature cat grass than lilies, or philodendrons, or string etc. So I can say that in many cases eating fresh, young cat grass at least does not appear to be bad for most cats. And that is about as concrete a statement that I can make in the argument FOR cats eating cat grass.
Mr Smith, my cat, checking out available vegetation
In summary, it is my opinion that you do NOT need to offer your pet cat cat grass. Cat grass ingestion probably does not have any true benefits for the normal, healthy cat, other than the distraction argument. It does make them vomit, but rarely is that a good thing. It does add fiber to the diet, but it is doubtful that that is necessarily a good thing, either. It is possible it may assist in a cat's ability to move hair through its intestinal tract, but a normal cat should be able to do that anyway without the added ‘benefit' of cat grass. And it is very unlikely it actually improves a cat's nutritional status. But it at least seems to be relatively harmless. So if you really want to feed your cat this vegetation, I will not try to stand in your way, as long as you understand it is not necessary, nor strongly recommended, at least by this veterinarian.