Fattori che influenzano il microbioma intestinale di cani in buon stato di salute.

The field of microbiome is a research topic in expansion, especially regarding the study of the gut microbiome in companion animals, in relation to diet and health status of the subject. Recently, several factors have been study to understand their influence on the variation of the microbial composition of the gastrointestinal (GI) tract. Unfortunately, there are a large amount of research with a few numbers of dogs per study. In particular, when it comes for nutritional investigation, the change in the diet corresponds to a modulation of one nutritional element per time, and a few researches take into account the effect of different type of diet – such as dry extruded diet Vs home-made diet – on the gut microbiome. The purpose of this doctoral thesis was to complement the information in the literature, by implementing a standardized method of analysis, from the collection of feces to the final taxonomic annotation, for all the studies carried out. Furthermore, the main aim was to form a sufficiently large database of data collected from healthy subjects. With this purpose, an attempt has been made to characterize the intestinal microbiome of healthy dogs. In the first place, we tried to understand if there were factors that influences the microbiome even in the absence of disease, in order to divide the subjects into macro-categories and to facilitate subsequent analyzes. The two factors initially identified were the type of diet administered and the sex of the animals, together with their hormonal status. Following these results, several studies have been conducted to confirm this hypothesis. Initially, a classic diet modulation study was carried out to verify whether the addition of a certain class of polyphenols could influence the intestinal microbial composition. Together with the analysis of the fecal microbiome, the level of serotonin and cortisol in saliva was also analyzed. Some changes were observed at the level of a single taxa during the course of the experiment, but not to induce a shift in the entire gut microbial composition. The level of serotonin, on the other hand, was strongly influenced by the addition of polyphenols in the diet, so further studies will be necessary to understand what is the action mechanism of polyphenols in GI tract. Subsequently, an attempt was made to analyze the metabolome of healthy dogs, using a new method that could determine, in addition to the specific metabolites, also the generic metabolic profile, and that did not destroy the samples after being analyzed. The implementation of this method has allowed us to appreciate how the metabolic profile also changes based on the type of diet that is administered to the dog. An innovative study, on the other hand, was the comparison of the fecal microbiome with that of the blood in healthy animals. Firstly, the primary objective was the verification of the presence of bacterial DNA in the blood of healthy dogs. Subsequently, another aim was the correlation of the intestinal microbiome with those of the blood. Unfortunately, the annotations were not overlapping, but in terms of beta diversity, both the fecal and the blood microbiome divided the subjects on the basis of the type of diet given to the animals. Finally, to conclude the results obtained so far, we wanted to do a network analysis on the database of healthy dogs analyzed at the beginning. This allowed a definition of the relationships existing between the microorganisms that make up the microbiome, and which relationships are significant based on the type of diet administered to dogs and their sex. This study provides a turning point in studies on the intestinal microbiome in dogs, establishing which relationships are useful for the definition of macro-categories of healthy subjects, and which are the threshold values of abundance of these key microorganisms for the definition of enterotype.