The comments on online forums are sometimes resigned, sometimes plaintive. One four-year-old "has always has some OCD issues," reports Brookey77, "especially when it comes to tennis balls. When he was a pup, he sucked on them as a baby would suck on a pacifier...Then he started eating them...For the last few months, he has been eating his leg."
An 8-month-old pitt bull is "a shadow chaser," says ultimatek9. "She is fine at night and when it is overcast, but when the sun comes out she goes into a trance. She locks onto the shadows and will start salivating and trembling."
Dogs with compulsion may pace, chase imaginary flies, or lick their flanks until they get sores, despite their owners' best efforts to make them stop. Certain breeds are especially vulnerable. A staple of canine compulsion is tail chasing, which frequently strikes bull terriers and German shepherds. On one forum, user MatrixsDad complains that his German shepherd "is constantly chasing and barking at her tail...She comes up and puts her backside against anyone who's standing around so she can get a better view of her tail before she starts chasing it."
Although they may seem like nothing more than cute YouTube material, dog compulsions can turn unfunny fast. A user called Fodder describes a cocker spaniel that used to chase and bite his tail whenever stressed. "Finally the day came—we pulled into the garage where he had been staying and he was cowering on the steps...as I got closer I realized that he was sitting in a puddle of his own blood. He had chewed his tail completely off."
Because of the apparent similarities between human OCD and dog compulsions, researchers led by Katriina Tiira at the University of Helsinki decided to investigate just how close the connection is. They gave detailed questionnaires to the owners of 368 German shepherds, bull terriers (standard and miniature), and Staffordshire bull terriers. Among their subjects, 218 were tail chasers.
The first clear similarity between tail chasing and human OCD is that they have a genetic component. In humans, OCD is estimated to affect 1 to 3 percent of the population in general. But the twin of a lifetime OCD sufferer has at least a 25 percent chance of OCD himself. Likewise, the fact that certain breeds of dogs chase their tails more suggests that somewhere in the breeding process, that tendency was embedded in their DNA.
The questionnaires turned up many similarities between obsessive dogs and humans. One was the early onset of the behavior: Human OCD often shows up in childhood or adolescence; tail chasing began for the greatest number of dogs in the study between 3 and 6 months old. Some dogs only tail chased occasionally, while others couldn't get enough and repeated the behavior several times a day. And some dogs also seemed to freeze or go into a trance, a symptom similar to one in human OCD patients called "obsessional slowness."
Certain factors appear to make dogs more or less likely to be tail chasers. Owners reported that tail-chasing dogs had been separated from their mothers earlier as puppies. Dogs that live with a lot of other dogs, though, don't chase their tails as often.
Dogs given vitamin and mineral supplements by their owners were less likely to tail chase, and so were females that had been neutered. This might mean that the presence of certain vitamins, or absence of certain hormones, makes tail chasing less likely. However, the authors acknowledge, it could also mean that owners who neuter their dogs or give them supplements are treating the dogs in some other way that lowers their risk of obsessive behaviors.
A subset of the dog owners in the study also filled out a questionnaire on the "personality" of their pets. Tail chasers were shyer and likely to have additional compulsions. Senior author Hannes Lohi says this resembles anxieties and behavioral inhibitions in human OCD sufferers.
"Our major aim is to identify new anxiety genes" in dogs, Lohi says. Those genes could teach us about how these conditions develop in dogs as well as in humans, who share the same environment and aren't that far off physiologically. We might even learn about new treatment avenues in humans. An earlier study found a genetic region that's linked to a flank-sucking obsession in Dobermanns—and the same region has been tied to human OCD and autism. But the new study found no connection between that genetic area and tail chasing.
It's likely, the authors write, that obsessive behaviors in dogs have many different origins and manifestations. The same seems to be true of humans. Hunting down the roots of these behaviors in our canine companions, then, might help us cure our own kinds of tail chasing.
Tiira K, Hakosalo O, Kareinen L, Thomas A, Hielm-Björkman A, Escriou C, Arnold P, & Lohi H (2012). Environmental effects on compulsive tail chasing in dogs. PloS one, 7 (7) PMID: 22844513