Benjamin Hart, DVM, PhD, who has studied animal behavior for almost 50 years, says that one of the questions he hears most frequently from pet owners is: “Why does my dog eat grass?”
Until recently, veterinarians like Hart could only speculate on the reason. Common theories included: The pet must be sick and needs to vomit. Or perhaps there is something wrong with his diet.
But according to new research by Hart and his colleagues at the University of California–Davis, neither of these answers appears to be correct.
With support from the school’s Center for Companion Animal Health, Hart studied 1,500 dogs that had eaten grass at least 10 times in the past year. They found that very few — about 9% — appeared to be ill before eating grass. And less than one in four vomited afterward. Diet or lack of fiber also had no effect on the dogs’ desire to eat these leafy greens.
So if most of these dogs weren’t sick, seldom vomited, and diet wasn’t a factor, why were they eating grass?
“We believe it’s a trait they inherited from their wild ancestors,” Hart says. “We know that wolves and cougars eat grass. That’s because they carry intestinal parasites. That’s just part and parcel of being in nature. Wild animals don’t have anything like the medicines we have for controlling worms. But by eating grass on a regular basis, they can prevent a buildup by purging their systems of these parasites.”
Hart’s study also revealed that younger dogs are more likely to eat grass than their adult counterparts.
“This is also true in nature,” he says. “Younger animals have weaker immune systems, and they need all the protein they can get in order to grow.”
So should you ever be concerned when your dog eats grass?
“Don’t allow your pet on a lawn that has recently been treated for pests or weeds,” Hart advises. If you are concerned about anything your dog has eaten, you should contact your veterinarian immediately.
Hart says that pet owners should be alert to any changes in a pet’s behavior, such as a sudden increase in grass eating.
“Keep in mind that 9% of the dogs we studied showed signs of illness before eating grass. This suggests that the dog is trying to medicate himself. Grass isn’t bad when you’re living in nature. But your veterinarian has far more effective medications to treat the problem.”
But What About Cats?
Cats eat grass less often than dogs, Hart says, but they tend to eat a wider variety of plants. This can present problems, because cats are increasingly kept indoors where the only plants available may be houseplants, several of which are poisonous. The 17 most common poisonous plants are listed in the table.
If your cat likes to eat plants, Hart suggests putting out a homegrown or commercial grass garden.
“By having grass readily available, cats will tend to avoid the other plants and will be less likely to go after something that might be toxic,” he says.
Common symptoms that might indicate plant poisoning are vomiting, diarrhea, excessive salivation and irritation of the lips.
If you suspect that your pet has eaten a poisonous plant, call your veterinarian or the ASPCA Animal Poison Control Center hotline at (888) 426-4435.