Companion Animal Behavior and the Microbiome

Does companion animal behavior influence the make-up of the animal’s microbiome? Or vice versa: Does the makeup of the animal’s microbiome influence companion animal behavior? Those questions and many others occurred to me after I read a study that explored the possible relationship between the gut biome and canine aggression. ( Kirchoff NS, Udell MAR, Sharpton TJ.2019. The gut microbiome correlates with conspecific aggression in a small population of rescued dogs (Canis familiaris). PeerJ 7:e6103 10.7717/peerj.6103 )

The authors’ results suggest that differences in the bacterial make-up of the microbiome could be associated  with canine aggressive and nonaggressive behavioral states.

The key phrase is “associated with”. It will take a lot more research to sort out all the variables that might be involved in just this one small population of shelter dogs seized from a dog-fighting organization. Much as I would love to see that magical verb “causes” instead of “associated with” or “correlates with”, this study raises more questions than it answers…Which is exactly what good science should do. It explores one small facet of a defined problem that might be associated with it. Then those same or other researchers will corroborate or refute those findings or conduct experiments on other elements that could be related to this same subject.

Granted this process can be incredibly slow.  But for those who take a more integrated view of animal behavior, such studies also serve as catalysts that trigger thoughts of  the possible implications related to this canine behavior-microbiome association.  I personally spent many happy hours bringing in wood, shoveling snow and otherwise battling the elements thinking about such mind/body behavior/microbiome interactive possibilities. And I spent a comparable amount of time enjoying similar discussions with interested friends.

On the one hand, the idea that the gut—or rather the itty bitty critters that call it home—can influence behavior seems more the stuff of sci-fi than science. But enough other studies in mice and humans support a behavior-biome correlation to convince me it’s for real. If I need more proof, I need only recall the  animals with behavioral problems I’ve encountered who also had  chronic or intermittent GI disturbances.

But wait. Doesn’t that stress-related churning gut phenomenon suggest that behavior could influence the gut instead of vice versa? Or could it be a combination of both?  I suspect both and a lot more. After all, other microorganisms beside bacteria call the gut home. Among these are viruses, yeasts,  and helminths (i.e., worms). The micro-lineup also includes protozoans, single-celled  creatures who may live either freely or as parasites. Try to resist any temptation to divide these normal denizens of the gut into beneficial or pathogenic factions because such thinking could create more problems than it solves.

Consider today’s new canine population in some areas: transport/rescue dogs who evolved to eat who-knows-what, where, for how many generations. Do dogs from long lines of successful scavengers or predators of small prey possess the same micro-organisms in their microbiomes? How do their microbiomes compare to that of generations of dogs fed diets manipulated by humans in one way or another?

Just as behavior and biome interactions may be mutually dependent on each other, so may those between diet and the biome. In that case, logic would argue that established canine scavengers would support microbiome populations that enable them to digest a wide variety of foods and  display the behaviors scavengers need to succeed. Meanwhile, successful canine predators would possess gut biomes that support the capture, consumption, and digestion of their prey. Scavengers wouldn’t need the ability to locate, kill, and digest a rabbit any more tha the free-roaming canine predator would need a microbiome that supports the location and digestion of moldy French fries, mac and cheese, and rotten fruit. In both groups, the successful microbiomes almost certainly would include a population of intestinal parasites.

Anyone who’s had to change their pet dog’s diet for some reason knows there’s a wrong way and a right way to do it. The wrong way is  stop feeding the old food one day and begin feeding  the new food the next. The right way involves gradually replacing part of the old diet with the new over a period of weeks. That’s the body side of the process.

However, there’s a behavioral/bond side of this process too. The switch-over goes much more smoothly if the dog likes the new food, and the owner believes the new food is better for the dog. If the dog doesn’t like the smell, taste, or texture of the food for some reason, life can get very complicated for dog and owner alike. And owners who consider it unloving to feed their dogs anything other than food from their plates will complicate this process for their dogs and themselves too.

Although we didn’t think of it this way in the pre-biome-awareness era, this gradual diet transition protocol most likely gives the mind/body microbiome time to adjust to its new food supply. In this case though, the dog’s diet and behavior regarding it change, whereas only the owner’s beliefs related to the new food change. Maybe.  (So much to know, so little time!)

But what about our transport/rescue dogs? I don’t recall anyone ever mentioning their rescue dog’s pre-rescue diet beyond labeling it “garbage” or “prey“, both of which were considered “bad”.  But regardless what these animals ate prior to rescue, they presumably ate whatever the rescuer considered a “good” diet post-rescue.  Nor do I believe—and I’d be overjoyed to learn otherwise—that much effort is made to ensure that these dogs were fed the same new diet through the capture, rescue, transport, and adoption process.

Oh, to be a microscopic drone hanging out in these dogs’ guts observing all the changes in the micro-flora and -fauna during all this! What wonderful things we might learn about how these different micro-organisms interact with each other as they seek to achieve physiological and mental stability with each other and the dog!  And while our friendly micro-drone collects that information, what we think of as “the dog” somehow magically processes this and a lot more data in her attempts to achieve behavioral, bond, and micro- and macro-environmental stability.

For now though, I must attribute any changes in the microbiomes of the tough canine survivors I see in my practice to divine intervention.  But as mere human mortals slowly unlock the biome’s secrets bit by bit, that undoubtedly will change. Already some of those results are pretty amazing.  Perhaps some wonderful day in the future, we’ll discover that the readily available, lowly,  and oft derided fecal sample truly does hold the keys to the human and animal mind-body kingdom.



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