Aaaah, the most asked question of dog owners! The simple answer…because your dog can!
Dogs are, what are called, opportunistic carnivores. What does that mean? It means they eat meat (carnivore) but they also eat other vegetable/grass/grain matter (opportunistic) if is available. I think some dog breeds are more opportunistic than others, like the labrador retrievers who eat just about anything! The definition (omnivore vs carnivore) has had a lot of debate because some think dogs may actually be omnivores (eat meat, plants, grains) much like people.
If you look at evolutionary biology and the development of the domestic dogs, our pet dogs developed all over the planet eating diets based on the ecology of the area. Certain dog breeds have better ability to digest starches (plants) better than others studies have found. We tend to lump “all dogs” into one group, just like we lump “all humans” into one group and make recommendations. As a general rule, dogs do well on diets that are meat based but they can survive (not necessarily thrive) on plant based items if need be.
So what about grass? If grass is available, they have the opportunity to eat it. I have four dogs. If food is available to all four of them, they will all eat it because of the competition present. If I take one of those dogs and separate them, they may not eat what I give them. I have eliminated the competition and they become more selective. So trying to decide why a dog eats grass can be very complicated. Some eat grass and then vomit. Perhaps they have an upset stomach and want to get rid of something. Some eat grass and don’t vomit. Perhaps they need more vegetable matter. Some don’t eat grass at all. Maybe because there is no competition or they simply don’t like grass.
My final answer is dogs eat grass because they can. You do not have to worry about it unless they are repeatedly vomiting, acting ill or your grass is laden with chemicals. See your veterinarian if they are eating grass and repeatedly vomiting. Keep them off the grass if you use chemicals and consider not using chemicals at all on your lawn. Stop worrying if its a problem–its okay and normal for the majority of dogs. I know what you’re going to ask next too…”Why does my dog eat poop?” More on that in a future blog post!