A short time ago a friend dropped by my house for a visit. We were sitting on my sofa sipping some wine and catching up on recent events when my Cavalier King Charles Spaniel, Ripley, jumped up beside me and began to lick my ear. My friend's face contorted in a look of disgust and she blurted out "Why do you let him do that? You don't know what he might have just eaten. I love my Gertie [her Labrador retriever] but I won't let her lick my face. She goes out into the backyard and eats her own poop. I can smell it on her breath and the thought of her licking me after she's eaten their own feces is revolting. I've tried everything to get her to stop doing that, but nothing seems to work."
It is well accepted that some dogs eat poop. They will eat their own droppings, that of other dogs, as well as the stools of other animals (I can't tell you how many times people have complained about their dog getting into the cat's litter box for a snack). The scientific term for this behavior is coprophagy. The eating of feces is widely distributed in the animal world, and among mammals it is found in rodents, rabbits, beavers, elephants and non-human primates, to name just a few. It is generally believed that the reason for this behavior is because, when an animal's diet is rich, digestion does not extract all of the useful dietary components, and eating the droppings of other animals provides a second chance for the animal to extract valuable nutrients. Humans tend to find this behavior in their pets to be gross and objectionable and it is listed in some studies as being among the top 10 reasons that dogs are surrendered to shelters.
It actually turns out that despite the fact that an Internet search will produce hundreds of pages discussing this problem, very little scientific data on the issue exists. However recently a new study on this issue appeared in the journal Veterinary Medicine and Science which tried to fill the gap in our understanding of this problem. The study was done by a team of investigators headed by the well-respected pair of animal researchers Benjamin and Lynette Hart, of the University of California at Davis. The research consisted of two web-based surveys. The first survey involved 1475 dog owners and was designed to see just how common this behavior was. The second survey looked at only 1552 dogs that were confirmed as being coprophagic and was designed to explore the reasons behind the behavior.
The data demonstrated the fact that 16 percent of dogs consume feces frequently (which means that their owners have seen them do it more than six times), while if you look at how many people have seen their dog do this at least once you bump the percentage up to 23 percent. The data also seems to show that the age of the dog made no difference, nor were there differences based on diet. The researchers also looked at whether coprophagy was associated with other compulsive behaviors, such as tail chasing, but found that that was not the case. Furthermore, the results showed that stool-eaters were just as easily housetrained as other dogs, a fact which seems to rule out the idea that the coprophagic dogs are just more comfortable with poop than their more discriminating peers.
Dogs who live in a household where there is more than one other dog were also more likely to be coprophagic, presumably since, with higher numbers of dogs around more poop is simply available. One personality factor which emerged was that the coprophagic dogs tended to be described as "greedy eaters".
I was somewhat surprised to see that in the first survey there was no significant sex difference. My surprise was because every female dog who has puppies ultimately becomes coprophagic, at least while the puppies are still very young. The reason for this is that females lick each puppy's urogenital and anal regions in order to stimulate them to urinate and defecate. In order to keep the nesting area clean, she then eats the waste products that the puppies produce. One might expect that such tendencies which are wired into female dogs might predispose them to eat stools in other situations. However, if I read the results of the second survey correctly, those results are different. Although the main text of the paper has no report on sex differences from the second survey, supplementary material which provides the raw data may is also attached. If that second survey is a true representation of coprophagic dogs, then female dogs are nearly twice as likely to be coprophagic (61 percent versus 39 percent for males) and this is a statistically significant difference.
The researchers also found that there are breed differences in the predisposition to eat droppings. When they analyzed the results by breed groupings they found that Hounds and Terriers are the breeds of dogs most likely to be coprophagic. When it comes to individual breeds, according to their data the little Shetland sheepdog is the greatest offender while Poodles appear to be the least likely to show this behavior.
When we focus on those dogs who are clearly coprophagic, we find that the dogs who eat poop tend to do it often. The survey showed that 62 percent ate stools daily and 38 percent did so weekly. However, these coprophagic dogs are not indiscriminate. Over 80 percent of the coprophagic dogs tended to only eat the poop that was fresh (no more than two days old). They selectively avoided any stools that were older than that. This apparently trivial observation actually led the researchers to hypothesize a reason why some dogs are coprophagic. They note that wolves typically defecate some distance away from their dens, partially because feces contain intestinal parasite eggs. They note however a sick or injured wolf might be forced to do its business at home. However, the droppings would not necessarily be dangerous immediately. Apparently, parasite eggs don't usually hatch into infectious larvae for several days. So if a wolf eats it right away the stool is safe to eat and the animal won't get infected by parasites. This led the investigators to suggest that coprophagic domestic dogs have inherited this wolf-like instinct to keep the region around their living area parasite-free thanks to the preventative treatment involving eating the droppings.
I know that some of you have persisted in reading this article, despite its distasteful topic, in the hopes that I would finally get to the point where the research would tell you how to solve this unpleasant problem in your own dog. However here the news is not so wonderful. The researchers tried to find out how successful dog owners had been using commercial products which are designed to make a dog's stools taste bad (as if dog droppings did not already taste bad). The foul taste is supposed to deter dogs from eating their stool. They tested 11 such products with names like "Deter", "Nasty Habit", and even one with the name "Potty Mouth". When it comes to the ability of these products to stop the poop eating they report that the success rate was dismal, ranging from 0 to 2 percent.
Behavioral methods and management techniques are not much more promising. Chasing dogs away from stools when they approach it, rewarding successful responses to the command "leave it alone", lacing stools with pepper, or punishing the dog by using electronic, sound emitting, or citronella dispensing collars have success rates which were reported in the 1 to 4 percent range.
So what are you supposed to do if your dog is engaging in this gross behavior? Well, that was the question which my friend asked me and I offered her the only advice which I know has any effect. That is to pick up the dog's droppings and dispose of them in a place that the dog has no access to. If you do this whenever your dog has a bowel movement you effectively prevent the behavior. As an old Baptist minister once proclaimed "If you remove the temptation you can prevent the sin."
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Hart, B. L., Hart, L.A., Thigpen, A. P., Tran, A. & Bain, M. J. (2018). The paradox of canine conspecific coprophagy. Veterinary Medicine and Science, DOI: 10.1002/vms3.92