Visiting Veterinarian : Chew on this
By Michelle Gerhard Jasny V.M.D.
Published: January 15, 2009
The world is full of mysteries. What happened to Amelia Earhart? Why is Mona Lisa smiling? What's the story behind Stonehenge? Why do dogs eat grass? Where's Waldo? We may never know the answer to many of these questions, but thanks to a few docs at the University of California at Davis School of Veterinary Medicine we now have a little scientific insight into one of those enigmas - the grazing habits of pet pooches.
So your dog, Ralph, likes to snack on the lawn. He is not alone. Eating grass, leaves, and other vegetation is frequently observed by dog owners. People have proposed many theories to explain this behavior, including boredom, dietary deficiencies, illness, and instinct. Biologists point out that wolves and coyotes prey on herbivorous animals such as mice, rats, deer, and rabbits. When Ralph's wild cousins consume these critters, they eat all the parts, often starting with the delectable entrails, which are full of vegetation. Perhaps Ralph has a natural taste for greens that is not satisfied by that bowl of Dog Chow served up nightly.
Here's another theory: Wild canids that scavenge for carrion may consume rotten meat, leading to food poisoning. Eating grass can irritate the stomach slightly and elicit vomiting, thus purging the system of spoiled food. Along the same lines is the proposition that eating plants is a natural way to treat intestinal worms, the fibrous vegetation getting tangled up with the parasites and dragging the worms out of the gut via the feces. This is not to say that Ralph (or his wild cousin Rolf) is consciously thinking, "That chunk of moose didn't sit too well. I'd better eat grass and barf." But what it might mean is that, historically, individuals who responded instinctively to gastrointestinal distress by eating plants might have been more likely to survive than individuals who did not. Then these plant-eaters would go on to reproduce, hence insuring any genetic predisposition to munching a little flora along with all that fauna would be passed on and amplified over generations in the population as a whole.
Does this mean Ralph eats grass only when he's not feeling well in an unconscious urge to make himself ralph? Researchers at UC Davis designed a survey to test this hypothesis. They questioned veterinary students with dogs, pet owners who brought their dogs to the UC Davis teaching hospital, and also conducted an online survey. With more than 3,000 responses, they weeded out those that did not meet the study criteria, ending up with 1,571 cases to evaluate. More than two-thirds of owners said their dogs ate plants on a daily or weekly basis. Were all these dogs sick? Nope. Only a small percentage showed signs of illness prior to eating the plants. Most of those did, in fact, vomit afterwards, but the majority of grass-eating pooches did not seem sick before grazing, did not vomit, and did not seem sick afterwards.
What about nutritional deficiencies? Nope. No correlation was found between Ralph's standard menu and his taste for vegetation. High-fiber food, raw diet, table scraps, the most expensive premium commercial dog chow available - none of these increased or decreased the likelihood of him mowing the lawn. The only trend noted was that younger dogs were observed eating plants more often than their elders. One doc speculated that this might be because youngsters are more susceptible to intestinal parasites, and that such parasitism could have a greater impact on an actively growing dog than on a mature one. Sounds good. On the other hand, as the mother of small children, my hypothesis is simpler. Kids (and puppies) will put anything in their mouths. As a group, grown-ups tend to be more discriminating.
The key is to know your dog and your environment. The other night a woman was grooming her two-year-old Cairn terrier, removing bits of sticks and burs that had tangled in the coat, wadding them up along with the fur that was brushing out. Suddenly, the pup grabbed a fur ball and swallowed it whole, complete with the small, prickly stick in the middle. The dog seemed fine initially, but at 3 am woke up and asked to go outside, where she proceeded to eat grass and try to vomit. "And she doesn't usually eat grass," her mom concluded as I examined the dog the following afternoon. In this case, grass eating was clearly a response to gastrointestinal distress. Luckily the stick passed in the feces the next day. Another friend's dog was not so lucky. After chewing up a pair of flip-flops and a rope toy, that dog also ate grass and tried to vomit, but ultimately ended up in surgery to relieve the intestinal blockage.
But these are the exceptions. If your Ralph regularly eats grass, don't worry, even if he ralphs afterwards. (I once heard a veterinarian opine that most dogs go around looking for a reason to vomit.) As long as Ralph seems healthy and is getting a balanced, nutritionally complete diet, let him graze - with a few precautions. Eschew greenery treated with fertilizers, herbicides, or pesticides. Check for poisonous plants. Avoid areas contaminated with animal feces. Have Ralph's stool tested regularly by your veterinarian for microscopic evidence of intestinal parasites. Steer clear of stuff like beach grass. These long, tough strands may not pass through his system as readily as the tender new shoots of grass that most dogs seem to prefer. The study ultimately concludes that consuming plant material is a normal canine behavior and generally not associated with illness, gastrointestinal or otherwise. The mystery is solved. For 25 years, whenever someone asked me, "Why do dogs eat grass?" I would reply, "Because they're dogs." And now it's official.
