Grass Allergies
Dogs have been eating grass without any side effects for, well since dogs have been around. Our dog eats grass all the time, especially the new grass that comes up between the rocks in our rock garden. Some, not all, of our other dogs have eaten grass occasionally. Molly is a Labrador Retriever and Labs tend to eat everything. She has not had any side effects from it, thrown up a couple times but I'm not convinced it was from the grass. If she decides it's not in her best interests, she will stop eating it on her own.
Grass Allergies
Nobody knows why dogs eat grass. There are a few theories out there. First one to come to mind is that they eat grass because they have an upset stomach and want to make themselves vomit. Another one is that they are trying to supplement their diet with greens, like we do with a salad. Another is that dogs are omnivores as opposed to carnivores, meaning they will "eat anything".
Grass Allergies
We have a lot of dogs in our neighborhood, many Labs and Beagles as we are in a hunting region, and all the dogs eat grass like cows. They also do not get any side effects, like vomiting, so I don't believe dogs eat grass to make themselves throw up. If they do, it could be because the grass they ate irritated their stomach lining. Dogs are quite capable of making themselves throw up without the aid of grass.
Grass Allergies
As far as supplementing their diet, most high quality dog food contain the nutrients your dog needs daily. With the key phrase here "high quality". If you only fed your dog canned meat, this theory could be valid. Feeding only canned meat is not healthy for their teeth or bowels being too soft. And dogs do need additional vitamins and minerals that are not contained in meat. Your dog is more likely to develop dental problems or constipation from the lack of fiber if they are only fed a canned meat diet.
Fertilizers and pesticides are very toxic to dogs, so if your dog eats grass you need to really keep an eye on him when they are out in an area that has or may have been treated with chemicals. Especially tempting are the clumps of grass that drop from the lawnmower but they can have gasoline or grease mixed in with them so be alert for those. One of the first commands we teach our dogs is "drop it". It is a great command to be able to use, especially when they are off leash.
Some things you can try are giving them some vegetables in their diet. Carrots and apples are good. Do not give them grapes, raisins or onions though. Those are toxic to dogs.
Dogs don't actually need variety in their diet like we do. Being creatures of habit, they are happy to eat the same thing day after day as long as it tastes good. Eating grass is just one of those things they do that doesn't hurt them and seems to make them happy.
Maybe the reason why dogs eat grass is because it just plain tastes good.
