Why Do Dogs Eat Grass?

All medical claims reviewed by Dr Pippa Elliott. BVMS, MRCVS.

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It’s one of life’s little mysteries: Why do dogs eat grass? Or is it.

But wait…you say…Dogs eat grass to make themselves sick. All dog owners know that!

A-ha! Gotcha.

Experts (presumably with plenty of time on their hands) have studied how many dogs vomit after eating grass. And the surprising answer is “Not very many.”

As it turns out, there’s quite a lot of myth and misinformation about dogs eating grass, so let’s put the record straight. It’s time to bust some myths about why dogs eat grass.

Myth Busting

#1: Dogs Eat Grass to Make Themselves Sick

Why do dogs eat grass to make themselves sick?

Does your dog eat grass then bring up a pile of froth afterwards?

It turns out this isn’t as common as you suppose.

The typical explanation for this is that fibre in the plant material rubs stomach lining and triggers them to be sick. Indeed, there’s an argument that their wild dog ancestors were omnivores (yes, that’s right, not pure carnivores, eating just meat but gobbling down the prey’s gut contents as well) and modern dog food is so highly refined that it doesn’t meet their inner urge for roughage.

Since 2008 there have been around four research projects looking at the frequency of vomiting after dogs eat grass. It turns out the percentage of dogs with a strong link to being sick afterwards is as low as 8% in one study, rising to 22% in another.

This still means less than a quarter of dogs that eat grass are regularly sick, so perhaps we should keep looking for our explanation.

#2: Dog Eat Grass when they have an upset stomach

Why do dogs eat grass when they are unwell?

Actually, it turns out that this also is a myth and there no evidence of a link between grass eating and ill health.

Those studies looking at the frequency of with which dogs vomited after eating grass, also inquired after the dog’s state of health. It turns out most herbage-eating hounds are bouncing with good health in the first instance.

Only a small number of grass-eating chowhounds, around 8% at most (from the study where 22% regularly vomited) showed signs of ill health before eating their organic dinner.

#3: Dogs Eat Grass because they Crave Fiber

These days many of our canines eat processed dog food consisting of kibble or canned meals. On the face of it, this processed food could well contain reduced amounts of fibre compared to a natural diet of a freshly killed rabbit. So the argument that dogs are seeking extra fibre at least sounds plausible.

Grazing on grass is indeed a natural source of vegetable fibre and roughage, which helps with regular bowel movements.

But guess what? There doesn’t seem to be a link.

Those ever-inquisitive scientists compared the grass-eating habits of dogs on naturally high fibre diets with those on low residue foods. It turns out which type of food the dogs ate had no statistical bearing on whether they ate grass or not.

Another grass-eating myth was blown out of the park. Heck, may they just like the taste of grass!

So Why Do Dogs Eat Grass?

It Purges Parasites

Actually, a dog eating grass mimics the behaviour of wolves and other wild dogs.

You guessed it….researchers picked through wolf poop and found grass fibre. Indeed, wolf stools can contain between 11 – 47% grass fibre. It turns out grass has natural deworming properties, which help to clear the gut of parasites.

The theory is that eating grass causes strong contractions of the gut wall, which dislodges intestinal worms. The grass blades then wrap round the parasites, pull them along for the ride, so they are passed out in poop.

However, this doesn’t mean pet owners should throw away those prescription worming medications. Grass eating can only ever lower a parasite burden, rather than fully eliminate them. And remember, our pet dogs live a lot longer than wild wolves, precisely because of the advantages of modern preventative care.

Don’t ditch the dewormers!

Should you let your dog eat grass?

It might just be that the green stuff tastes nice to dogs. But should you let your dog eat grass?

If the grass is growing naturally and not covered in pesticides, there’s little harm in a dog or puppy eating it. Indeed, most dogs seem to enjoy eating grass, so leave them to it.

However, one word of caution. Eating a lot of long grass does carry a slight risk of causing a particular type of bowel obstruction. Those long grass blades can twist together to form a long string-like length of knotted stalks. If one ends becomes anchored in the stomach and the other end travels down the intestine, this can cause the gut to concertina upon itself.

Although rare, this condition is like having a linear foreign body and can have serious consequences. The signs of this complication include extreme dullness, uncontrollable vomiting, and lethargy. And the treatment is surgical removal of the grass from the intestine. Ouch!

Why do dogs eat grass? An instinctive urge to get rid of parasites seems the strongest contender.

Can dogs eat grass? Yep, but just be sure to cut the lawn regularly to avoid chowing down on long blades.

If your herbage hound likes to go green, there’s no need to stop him. But as to why he loves the green stuff…it could be as simple as they like the taste of grass.

And finally, is eating grass as a sign of pica (craving unusual foods, often linked to nutritional deficiency) or one of the more subtle signs of illness? Maybe. Dog owners know their dog, and if it’s unusual for your best buddy to nibble on grass, then take note. Whilst normal dogs may eat grass, if this is unusual dog behavior then it could be significant and consider getting your pet pal checked by a vet.

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