(Originally written for DogWatch, a newsletter for the general public from the Cornell University College of Veterinary Medicine)

Recently I was shocked to discover my dog eating my cat’s stool out of the litter box. When I mentioned this to a collection of other dog owners, one said her dog rolls in animal waste, and a third confessed his dog eats its own stool. Is this normal dog behavior or is something strange going on in my neighborhood?

When we discover our dogs happily munching animal feces or catch a whiff of manure on a beloved pet’s coat or breath, we often react more emotionally than scientifically. Rather than analyzing why the behavior occurred, most of us become consumed with the idea of brushing the animal’s teeth, gums, and tongue and/or giving it a bath, ideally as quickly as possible and without retching.

However, although any kind of canine fecal focus strikes most of us as abnormal (and disgusting!), dogs come by their interest legitimately and paying closer attention to the behavior may reveal some very interesting facts.

When canine fecal fascination exists, several questions should pop into mind:

  • Is the dog playing with the waste, rolling in it, or eating it?
  • If the dog is eating the stool, whose stool is it eating? Another animal’s or its own?
  • If another animal’s stool, does the waste belong to a member of another species or to another dog?

In the winter in colder climates, some dogs delight in flipping frozen cow flops into the air and catching them. Owners who report this behavior note that they can trade their pets over to a ball or Frisbee, but the latter don’t hold quite the appeal. The reason why dogs may feel this way brings us to animals who roll in or eat stool.

Although no conclusive evidence exists regarding why dogs roll in other animal’s waste (as well as dead animal parts), it seems reasonable to assume they do this to provide themselves with a sort of camouflage. Animal waste carries a rich supply of pheromones, potent chemicals that reveal its source’s species, sex, reproductive status, and even social rank. Because many mammals rely on scent rather than vision to identify each other, a dog who rolls in waste or other debris from a member of another species could conceivably fool members of that species into accepting it as one of their own. In the wild, this would enable a predatory dog to get closer to a potential meal than it could otherwise, thereby improving its chances for survival. Because of the survival advantage the behavior conferred, it would become firmly entrenched in the wild dog’s repertoire and persist even after domestication.

Dogs who eat other animals’ waste usually eat that belonging to a species possessing different nutritional requirements. For example, cats require a much higher protein diet than dogs, and the horses, cattle, sheep, deer, and rabbits which serve as the sources of the meadow muffins and field raisins so relished by many dogs feed on grasses and plants. Given these different diets and digestive products, these other animals’ “waste” isn’t waste to the dog at all, but rather an alternative food source. Moreover, because this material has already received some processing, it may provide the dog with nutrients it couldn’t gain from eating that animal’s food directly. Thus, while we rarely see wolves eating vegetation, wolves often first zero in on the vegetation-stuffed stomach and intestinal tract of their plant-eating prey following a kill.

Dogs who eat their own stool also may do so because they perceive it more as food rather than waste. In this case, however, the behavior may result because the dog can’t completely digest its food for some reason. For some dogs, a lack of the necessary digestive enzymes to break down the nutrients in certain kinds of food may cause the problem. Others may experience problems that interfere with their ability to absorb the nutrients from their digestive tracts. A third group may eat stool simply because it’s become a habit. Because medical or behavioral problems may cause the problem, dogs who eat their own stool should be examined by a veterinarian.

Dogs who eat other dogs’ stool generally do it for one of two reasons. Occasionally a very timid dog may eat another dog’s stool in an attempt to remove the intruder’s “mark” from its own territory. Other dogs who eat dog stool may do if the other animal suffers from the aforementioned digestive problems.

Admittedly, none of us likes the idea of our pets rolling around in or eating waste. On the other hand, and like a lot of other seemingly uncouth canine behaviors, this one, too, offers us a glimpse of the fascinating world in which our dogs live.