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Rescue dogs study

Oregon State University researchers, from left Monique Udell, Thomas Sharpton and Nicole Kirchoff are shown in a laboratory at Nash Hall. The trio recently completed a study that indicates that microbes in the guts of rescue dogs can sometimes signal that a dog is aggressive.

What makes dogs aggressive?

Three Oregon State University researchers say the key might — emphasis on might — have something to with microbes in the guts of canines.

Nicole Kirchoff, a graduate student in microbiology, Monique Udell, an assistant professor and animal behavior researcher, and Thomas Sharpton, an assistant professor who specializes in microbiology and statistics, published a paper on the topic Jan. 9 in PeerJ, an open access scientific journal that posts articles on a range of topics.

Following up on research that has been done with mice and anxiety disorders, the researchers worked with a rescue dog organization on its study. The research involved 31 “pit bull-type dogs” who had been tested for aggressiveness. The OSU group then tested their feces for the presence of microbes.

The research revealed that there is a clear link between aggressive behavior and the types of microbes that live in the dogs’ guts. The research group stopped short of saying the composition of a dog’s gut microbiome causes aggressiveness, or vice-versa — only that there are statistical associations between how an animal acts and the microbes it hosts.

“In terms of how microbes potentially influence dog behavior, this lays the foundation for how aggression and gut microorganisms may be connected,” said lead author Kirchoff. “To our knowledge no other study has looked at the relationship between dog aggressiveness and gut microbes.”

Firmicutes, fusobacteria, bacteroidetes and proteobacteria were the dominant microbes among all stool samples, but their presence differed significantly between aggressive and nonaggressive animals. Proteobacteria and fusobacteria were more abundant in relative terms in nonaggressive dogs, whereas firmicutes was relatively more abundant in dogs showing aggression.

Domesticated dogs have lived with humans for more than 14,000 years, are among the most popular companion animals and forge strong bonds with both people and other animals. But aggressive behavior nevertheless remains a common problem and in many cases leads to animals being euthanized.

“Aggression is really stigmatized,” said Udell. “It tends to get viewed as a shortcoming of the individual animal. But it’s important to look at aggression and other behavioral syndromes in terms of physiology as well. Maybe there are underlying physiological causes we can address, or if not, maybe there are behavioral predictors with physiological implications.”

The researchers emphasized that they haven’t proven anything yet and that more research is needed. Sharpton said the findings first need to be validated in a small population of dogs and then work should be done with additional dogs and additional breeds.

“Maybe there’s a microbiome component that contributes to aggressiveness, but we need follow-up experimentation to determine if there is a causative role,” Sharpton said. “We’ve opened a new door. It will require appropriate resources to find out what is on the other side.”

Sharpton said that such support could come from the community, foundations or corporations.

Also dangling out there is the question of how the microbes get into dog guts to begin with. The researchers say it could be a function of genetics or their environment.

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Contact reporter James Day at or 541-758-9542. Follow at or