Why do dogs eat poop?

Theories abound: They’re bored; they have enzyme deficiencies; it’s a problem with the pancreas; they do it for attention (if so, it’s working, but maybe not the way they were hoping); they like the taste (ugh); and, most annoying of all, they’re just really, really, hungry.

Jeez, dude. Wait for dinner! It’s not that far away . . .

But so far, there hasn’t been a lot of convincing evidence for any of these answers. Now, new research suggests that dogs might eat their own poop for the most counter-intuitive of reasons:

To keep from getting sick.

Contacted by email, study co-author Benjamin Hart, DVM, PhD, and director of the Center for Animal Behavior at Davis, concedes that there are a lot of opinions on this problem without any data to back them up, adding, “I think because writers of websites, veterinarians, and others want to say something other than ‘I don’t know.’” 

So, Hart and a team of veterinary researchers at the University of California, Davis, surveyed thousands of dog owners on their pets’ poop-eating habits. Technically, eating feces is called coprophagy, and it’s normal behavior among many animals. According to the survey, 16% of dogs regularly eat feces, either their own or another animal’s. And while eating feces isn’t necessarily good for dogs, it isn’t necessarily harmful, either. The biggest problem with coprophagy is that people get upset by it.

Hart says, “This behavior is very, very disturbing to dog owners and thus, veterinarians are asked frequently about why this occurs and what can be done to stop it.” It’s so disturbing that some dog owners will rehome a coprophagous dog, or even use it as an excuse to have him euthanized. “As a behaviorist I decided it was time to collect enough data about frequently-stool-eating dogs to test some of the more common ideas.”  

Among the common ideas they tested, Hart and his team found no evidence that coprophagy is related to a dog’s age or diet. Nor did they see a link between sex or sexual status (although this finding conflicts with an earlier study that did find a correlation—specifically, that intact female dogs were more likely to eat feces than intact males, and that neutering increased the proportion coprophagous dogs from 34 % to 55.8 %).

Nor was there any correlation with ease of housetraining or compulsive behavior.

What they did find was that owners of coprophagous dogs were much more likely to describe them as “greedy eaters.” They were more likely to be found in multidog households, where you would also expect to find a greater concentration of stools, i.e., more targets of opportunity. And there was a slight association with breed group, showing terriers and hounds as the most likely to eat feces, and poodles the least.

More significantly, better than 80% of coprophagic dogs preferred their feces fresh. Less than two days old, in most cases.

Older than that, and most of the dogs weren’t interested. And this freshness finding supports the researchers’ main hypotheses: that coprophagic behavior in dogs is an adaptive evolutionary mechanism that dates back more than 15,000 years.

Wolves did it (and still do).

The researchers point out that wolves usually defecate away from their dens, in part because their feces contain intestinal parasite eggs. But if a wolf was too sick or injured to move and had to defecate at home, those parasitic eggs became a potential problem. But because parasite eggs don’t typically hatch into infectious larvae for a couple of days, the feces wouldn’t necessarily be dangerous right away.

So, what to do with the poo? You can see where this is going.

The researchers theorize that wolves would eat the feces to get rid of it and protect the pack. And while that might sound extreme, remember that it’s not like those wolves had a pooper scooper handy. Or the opposable thumbs necessary to use one if they did. And if they ate it fresh, right away, before the larvae eggs hatched, it would be safe to eat.

Smart wolves.

Now the bad news. Or, if your dog is coprophagic, maybe more bad news.

The survey also quizzed the dog owners on the effectiveness of 11 commercially available food additives and tablets that claim to treat coprophagy. Respondents reported a success rate of between zero and 2 percent.

You’ll have slightly better luck breaking a coprophagic dog’s poop-eating habits with behavioral training, like saying “Good dog,” and offering him a treat when he poops. That works in up to 4 percent of cases.

Just make sure the treat is tastier than the alternative.

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