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Domesticated dogs are among the most popular companion animals and forge strong bonds with both people and other animals. But aggressive behaviour nevertheless remains a common problem and in many cases leads to animals being euthanised. To some, the role of gut microorganisms in canine aggressiveness and other psychological symptoms may seem far fetched, but is it really?


Microbiota refers to the entire population of microorganisms that colonizes a particular location; and includes not just bacteria, but also other microbes such as fungi, archaea, viruses, and protozoans[]. Significant interest have evolved on the gut microbiota in the recent years within the scientific community; and the gut microbiota have been associated with a large array of human diseases ranging from luminal diseases such as inflammatory bowel diseases (IBD)[] and irritable bowel syndrome (IBS)[], metabolic diseases such obesity and diabetes[], allergic disease[] to neurodevelopmental illnesses, though the strength of evidence is not robust with many of them. It has been speculated since long that the gut microbiota bear significant functional role in maintaining the gut in the normal individual and human health as a whole. There is now mounting evidence resulting from studies on humans and germ free mice that supports these speculations. Several high quality data from the US Human Microbiome Project (HMP)[], European Metagenomics of the Human Intestinal Tract (MetaHIT)[] and several other studies have now demonstrated the beneficial functions of the normal gut flora on health down to the genetic level.

From an immunological perspective, microorganisms are viewed as pathogens by the host immune system that recognizes and eliminates them. However, majority of the gut bacteria are non-pathogenic and, co-habit with the enterocytes in a symbiotic relationship. The gut commensals predominantly aid in nutrient metabolism, drug metabolism, prevention of colonization of pathogenic microorganisms and in intestinal barrier function. At the same time, the immune system has co-evolved to live in a collaborative relationship with the healthy microbiota, while serving its function to fight off invasive pathogenic microorganisms.


The concept of intestines as second brain has been known to science for some time now. "The enteric nervous system (ENS) contains millions of neurons essential for organisation of behaviour of the intestine," wrote the team of researchers from Australia who observed the so-called second brain hard at work using a combination of high-precision neuronal imaging techniques. However this "second brain" seems to be controlling not only our guts but also our "primary" brain i.e our psyche. In her ground breaking book Gut and the Psychology Syndrome Dr Natasha Campbell Mcbride explains all the intrcacies of this highly sophisticated mechanism or cascade of events. I cannot recommend this book strongly enough not just those suffering from mental disorders but to anyone who is interested in leading healthy and productive life. Certain microorganisms thrive on certain foods, highly processed foods rich in complex carbohydrates favour certain types of bacteria and these bacteria, through domino effect can wreck havoc both on our physical and mental health. Therefore, by manipulating our diet we can manipulate our mental health.
Natasha has been proving this theory in practice. Since 1998 she has successfully treated wide variety of mental disorders for which there is not cure according to conventional wisdom, from autism to schizophrenia..



Last week OSU College of Science published a groundbreaking study of more than two dozen rescued dogs, some aggressive and some not, which  showed a clear link between aggressive behavior and the microbes that live in the dogs’ guts. The findings, published today in PeerJ, stop 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 Nicole Kirchoff, a graduate student in microbiology in the OSU College of Science. “To our knowledge no other study has looked at the relationship between dog aggressiveness and gut microbes.”

The study involved 31 “pit bull type dogs,” 14 males and 17 females, who were living at a temporary shelter after having been rescued from a dogfighting operation.Upon reaching the shelter, and prior to the start of the research, each dog was put through a series of tests by an animal welfare agency and categorized as aggressive or non-aggressive. Animal welfare workers also collected a fecal specimen from each animal so the scientists could analyze the dogs’ gut bacteria.

Firmicutes, Fusobacteria, Bacteroidetes and Proteobacteria were the dominant phyla among all stool samples, but their abundance differed significantly between aggressive and non-aggressive animals.Proteobacteria and Fusobacteria were more abundant in relative terms in non-aggressive dogs, whereas Firmicutes was relatively more abundant in dogs showing aggression.

Other microbiome differences between aggressive and non-aggressive dogs were observed at the operational taxonomic unit, or OTU, level; an OTU classifies groups of closely related organisms. Seven OTUs differed significantly between dogs that were aggressive and those that were not aggressive: four from the genus Dorea, two from Lactobacillus and one from Turicibacter.

Also among the findings: Nine clades within the Bacteroides genus were elevated in the gut microbiomes of the non-aggressive dogs, and 25 clades from Lactobacillus were relatively abundant in aggressive animals; a clade is a group of organisms thought to have descended from a common ancestor.

We’re finding associations between types of organisms in the gut and aspects of vertebrate physiology we wouldn’t have hypothesized about prior to the emergence of microbiome research over the last couple of years,” said co-author Thomas Sharpton, a microbiology and statistics researcher in OSU’s College of Science. “The gut-brain axis, the reciprocal communication between the enteric nervous system and mood or behavior, is a rapidly growing and exciting body of research.


The role these tiny organisms play in overall health is fascinating if not mind-boggling. I sincerely believe that future of medicine be it human or veterinary, lies in complete understanding of this role. This research is still in its infancy but what we already know only reinforces my belief that the only way to vibrant health both for us and our furry companions is through species appropriate natural food and complete elimination of processed foods rich in complex carbohydrates. Antibiotics can indeed save lives in certain situations but they are largely misused and abused in both human and veterinary medicine. We can only hope for new advances in microbiota research which will put an end to this.



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