My childhood dog, Sammy, enjoyed eating cat vomit and trash (in general), and once she ate a live toad. What Sammy truly enjoyed, however, was poop — whether it was her own or the feces of her brethren. Why dogs like Sammy eat poop is somewhat of a zoological mystery, and veterinarians can offer only vague hypotheses when owners ask why their dogs lust for number two.

Scientists from the University of California, Davis recently took a stab at answering this question in a paper published on January 12. In Veterinary Medicine and Science, they explain that the predisposition of some dogs to eat poop — a practice formally called canine conspecific coprophagy — is somewhat of a paradox. Dogs typically do their business away from where they sleep, creating some distance between themselves and the poop, so it doesn’t seem to make sense that their taste for turds has persisted throughout the years.

While it’s been theorized that dog coprophagy could be triggered by malnourishment or digestive enzyme deficiencies, this new paper offers a different argument: Eating poop, the researchers write, could be a “variant of an innate behavioral predisposition, possibly stemming from wolf ancestors.” Ancient wolves, they explain, kept their dens free of feces from sick members of the pack by eating their fresh droppings.

dog poop
Will this dog eat her poop? Maybe.

By doing this, they could keep the rest of their pack away from fecal-born intestinal parasites. Larvae found in poop can’t cause sickness, but they can become living, harmful parasites within two days after a dump is dropped. So, wolves — and now our good boys — make sure to eat the poop while it’s fresh to eliminate the larvae before they become a threat. The scientists describe this as an “evolved parasite defense strategy.”

Study author Benjamin Hart, Ph.D. told the Washington Post that, while the case isn’t closed on poop eating, this is the most logical explanation that they have. Hart and his team came to it by conducting the first data-based, published study on the prevalence of coprophagy in domestic dogs. They used the data from two web-based surveys filled out by dog owners: one covered 1,552 poop eaters and their classier peers, and another collected data on 1,475 poop-eating dogs with owners that tried using professional treatments to stop the feces eating.

wolf
Wolves may have given dogs the habit of eating poop.

The analysis showed that 16 percent of the dogs engaged in “frequent coprophagy,” meaning they had been seen by their owners eating stool at least six times. Dogs that were house trained were just as likely to be coprophagic as the others, and there was no link between a dog’s diet and its proclivity for poop eating. What did unite the coprophagic dogs was their relatively higher categorization as “greedy eaters” that overwhelmingly chose to eat stool fresher than two days old. This observation supports the idea that some evolutionary cue is telling them to eat the poop before larvae hatches.

Interestingly, while modern wolves still carry intestinal parasites, present-day dog poop is usually parasite-free thanks to preventative medical treatments. Your pup’s lingering coprophagic desires, it seems, are just innate impulses left over from their wolf days.

The study also showed that none of the preventative poop eating treatments on the market — neither Potty Mouth nor For-Bid — worked. Designed to make poop taste really bad, these treatments were zero to two percent likely to be effective. It’s unfortunate for grossed-out dog owners, but knowing this, Hart and his team have decided to try to begin clinical trials and invent a treatment of their own. They have science on their side, but they’ll also be fighting thousands of years of evolution.


You’ve made it to the end! Now watch some robot dogs.