Gut Microbiome Composition is Associated with Age and Memory Performance in Pet Dogs

Large intestinal nutritional and physicochemical parameters from different dog sizes reshape canine microbiota structure and functions in vitro

Different dog sizes are associated with variations in large intestinal physiology including gut microbiota, which plays a key role in animal health. This study aims to evaluate, using the CANIM-ARCOL (Canine Mucosal Artificial Colon), the relative importance of gut microbes versus physicochemical and nutritional parameters of the canine colonic environment in shaping microbiota structure and functions. CANIM-ARCOL was set up to reproduce nutrient availability, bile acid profiles, colonic pH, and transit time from small, medium, or large dogs according to in vivo data, while bioreactors were all inoculated with a fecal sample collected from medium size dogs (n = 2). Applying different dog size parameters resulted in a positive association between size and gas or SCFA production, as well as distinct microbiota profiles as revealed by 16S Metabarcoding. Comparisons with in vivo data from canine stools and previous in vitro results obtained when CANIM-ARCOL was inoculated with fecal samples from three dog sizes revealed that environmental colonic parameters were sufficient to drive microbiota functions. However, size-related fecal microbes were necessary to accurately reproduce in vitro the colonic ecosystem of small, medium, and large dogs. For the first time, this study provides mechanistic insights on which parameters from colonic ecosystem mainly drive canine microbiota in relation to dog size. The CANIM-ARCOL can be used as a relevant in vitro platform to unravel interactions between food or pharma compounds and canine colonic microbiota, under different dog size conditions. The potential of the model will be extended soon to diseased situations (e.g. chronic enteropathies or obesity).

The Relationship between Canine Behavioral Disorders and Gut Microbiome and Future Therapeutic Perspectives

Canine behavioral disorders have become one of the most common concerns and challenging issues among dog owners. Thus, there is a great demand for knowledge about various factors affecting dogs' emotions and well-being. Among them, the gut-brain axis seems to be particularly interesting, especially since in many instances the standard treatment or behavioral therapies insufficiently improve animal behavior. Therefore, to face this challenge, the search for novel therapeutic methods is highly required. Existing data show that mammals' gut microbiome, immune system, and nervous system are in continuous communication and influence animal physiology and behavior. This review aimed to summarize and discuss the most important scientific evidence on the relationship between mental disorders and gut microbiota in dogs, simultaneously presenting comparable outcomes in humans and rodent models. A comprehensive overview of crucial mechanisms of the gut-brain axis is included. This refers especially to the neurotransmitters crucial for animal behavior, which are regulated by the gut microbiome, and to the main microbial metabolites-short-chain fatty acids (SCFAs). This review presents summarized data on gut dysbiosis in relation to the inflammation process within the organism, as well as the activation of the hypothalamic-pituitary-adrenal (HPA) axis. All of the above mechanisms are presented in this review in strict correlation with brain and/or behavioral changes in the animal. Additionally, according to human and laboratory animal studies, the gut microbiome appears to be altered in individuals with mental disorders; thus, various strategies to manipulate the gut microbiota are implemented. This refers also to the fecal microbiome transplantation (FMT) method, based on transferring the fecal matter from a donor into the gastrointestinal tract of a recipient in order to modulate the gut microbiota. In this review, the possible effects of the FMT procedure on animal behavioral disorders are discussed.

Comparative Analysis of Gut Microbiota between Captive and Wild Long-Tailed Gorals for Ex Situ Conservation

The long-tailed goral is close to extinction, and ex situ conservation is essential to prevent this phenomenon. Studies on the gut microbiome of the long-tailed goral are important for understanding the ecology of this species. We amplified DNA from the 16S rRNA regions and compared the microbiomes of wild long-tailed gorals and two types of captive long-tailed gorals. Our findings revealed that the gut microbiome diversity of wild long-tailed gorals is greatly reduced when they are reared in captivity. A comparison of the two types of captive long-tailed gorals confirmed that animals with a more diverse diet exhibit greater gut microbiome diversity. Redundancy analysis confirmed that wild long-tailed gorals are distributed throughout the highlands, midlands, and lowlands. For the first time, it was revealed that the long-tailed goral are divided into three groups depending on the height of their habitat, and that the gut bacterial community changes significantly when long-tailed gorals are raised through ex situ conservation. This provides for the first time a perspective on the diversity of food plants associated with mountain height that will be available to long-tailed goral in the future.

Associations between memory performance and Bifidobacterium pseudolongum abundance in the canine gut microbiome

Memory has been identified as the least heritable cognitive trait in canines, suggesting a significant influence of non-genetic factors. We observed a trend that overall memory scores (OMS) improve with age in a cohort of 27 young dogs, but considerable plasticity exists. Employing linear discriminant analysis of gut microbiome data from dogs exhibiting low and high OMS, a single bacterial species, Bifidobacterium pseudolongum, was identified and confirmed to be correlated with elevated OMS. Subsequent analysis using a random forest regression model revealed that sex, litter, and breed identity had minimal predictive importance. Age had some predictive value but failed to achieve statistical significance in this dataset. In sharp contrast, the abundance of 17 bacterial taxa in the microbiome showed a stronger predictive capacity for memory performance. Our findings provide insights into microbiome underpinnings of mammalian cognitive functions and suggest avenues for developing psychobiotics to enhance canine memory and learning.

Microbiota insights into pet ownership and human health

The relationship between pet and owner has already been studied in several studies. Reviewing and summarizing studies on human and pet microbiota and their effects due to keeping pets is the purpose of the current study. Microbiota of the gut, oral cavity, and skin are unique to each individual, and this is also true of their pets (cats and dogs). Microbiota homeostasis is essential for the health of pets and their owners. Dysbiosis or imbalances in the microbiota can increase the risk of disorder progressions such as IBD or Clostridium difficile infections, among others. The microbial communities of humans change as a result of various factors, such as keeping pets. Pet owners frequently contact domestic dogs and cats, which affects their microbiota. As a result of keeping pets, the microbiota of different areas of the human body has changed, which has been associated with a decrease in pathogenic bacteria and an increase in beneficial bacteria.

A revisiting of "the hallmarks of aging" in domestic dogs: current status of the literature

A progressive decline in biological function and fitness is, generally, how aging is defined. However, in 2013, a description on the "hallmarks of aging" in mammals was published, and within it, it described biological processes that are known to alter the aging phenotype. These include genomic instability, telomere attrition, epigenetic alterations, loss of proteostasis, deregulated nutrient sensing, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication (inflammation), and changes within the microbiome. This mini-review provides a detailed account of the progress on each of these hallmarks of aging in the domestic dog within the last 5 years. Additionally, when there are gaps in the literature between other mammalian species and dogs, I highlight the aging biomarkers that may be missing for dogs as aging models. I also argue for the importance of dog aging studies to include several breeds of dogs at differing ages and for age corrections for breeds with differing mean lifespans throughout.

Gut-Brain Axis Impact on Canine Anxiety Disorders: New Challenges for Behavioral Veterinary Medicine

Anxiety disorders in dogs are ever-growing and represent an important concern in the veterinary behavior field. These disorders are often disregarded in veterinary clinical practice, negatively impacting the animal's and owner's quality of life. Moreover, these anxiety disorders can potentially result in the abandonment or euthanasia of dogs. Growing evidence shows that the gut microbiota is a central player in the gut-brain axis. A variety of microorganisms inhabit the intestines of dogs, which are essential in maintaining intestinal homeostasis. These microbes can impact mental health through several mechanisms, including metabolic, neural, endocrine, and immune-mediated pathways. The disruption of a balanced composition of resident commensal communities, or dysbiosis, is implicated in several pathological conditions, including mental disorders such as anxiety. Studies carried out in rodent models and humans demonstrate that the intestinal microbiota can influence mental health through these mechanisms, including anxiety disorders. Furthermore, novel therapeutic strategies using prebiotics and probiotics have been shown to ameliorate anxiety-related symptoms. However, regarding the canine veterinary behavior field, there is still a lack of insightful research on this topic. In this review, we explore the few but relevant studies performed on canine anxiety disorders. We agree that innovative bacterial therapeutical approaches for canine anxiety disorders will become a promising field of investigation and certainly pave the way for new approaches to these behavioral conditions.

Investigating causal associations among gut microbiota, metabolites and autoimmune hypothyroidism: a univariable and multivariable Mendelian randomization study

Background

Accumulating evidence suggests that the gut microbiota and its metabolites may be involved in autoimmune hypothyroidism. However, the causal association between gut microbiota, metabolites and autoimmune hypothyroidism remains to be determined.

Methods

Instrumental variables were screened from the GWAS datasets of 211 gut microbiota taxonomic groups, gut microbiota-derived metabolites, and autoimmune hypothyroidism. Univariable Mendelian randomization (MR) and multivariable Mendelian randomization (MVMR) were used to analyse the potential causal relationship between autoimmune hypothyroidism, these metabolites, or these microbiota. During the MR analysis, we alternated multiple MR methods with different model assumptions to assess the consistency and robustness of the findings: inverse variance weighted (IVW), weighted median, MR pleiotropy residual sum and outlier (MRPRESSO) and MR-Egger methods. Reverse MR analysis was performed to assess the possibility of reverse causality. Finally, enrichment analyses were used to investigate potential biofunctions.

Results

The IVW results of univariable MR showed that the phyla Actinobacteria, genus DefluviitaleaceaeUCG011, genus Eggerthella, family Defluviitaleaceae, genus Subdoligranulum, genus RuminococcaceaeUCG011, and genus Intestinimonas were associated with autoimmune hypothyroidism. After FDR adjustment, the absence of a causal relationship between gut microbiota and autoimmune hypothyroidism (PFDR > 0.05) suggested a possible marginal association. The results on gut metabolites showed that N-(3-furoyl)glycine, pipecolate, phenylalanine, allantoin, indololactate and alanine were associated with autoimmune hypothyroidism. After FDR correction, only indololactate was associated with hypothyroidism (OR=1.592; 95% CI, 1.228-2.065; PFDR= 0.036). Family Defluviitaleaceae and genus DefluviitaleaceaeUCG011 were suggestively significant in the MVMR. The results of reverse MR analysis showed no reverse causality between autoimmune hypothyroidism and the identified gut microbiota. Enrichment analysis revealed that several key regulatory pathways were significantly enriched.

Conclusion

This study supported that there were beneficial or detrimental causal effects of gut microbiota and its metabolites on autoimmune hypothyroidism risk, which provides more theoretical support for mechanistic research on the "thyroid-gut" axis.

New methods to unveil host-microbe interaction mechanisms along the microbiota-gut-brain-axis

Links between the gut microbiota and human health have been supported throughout numerous studies, such as the development of neurological disease disorders. This link is referred to as the "microbiota-gut-brain axis" and is the focus of an emerging field of research. Microbial-derived metabolites and gut and neuro-immunological metabolites regulate this axis in health and many diseases. Indeed, assessing these signals, whether induced by microbial metabolites or neuro-immune mediators, could significantly increase our knowledge of the microbiota-gut-brain axis. However, this will require the development of appropriate techniques and potential models. Methods for studying the induced signals originating from the microbiota remain crucial in this field. This review discusses the methods and techniques available for studies of microbiota-gut-brain interactions. We highlight several much-debated elements of these methodologies, including the widely used in vivo and in vitro models, their implications, and perspectives in the field based on a systematic review of PubMed. Applications of various animal models (zebrafish, mouse, canine, rat, rabbit) to microbiota-gut-brain axis research with practical examples of in vitro methods and innovative approaches to studying gut-brain communications are highlighted. In particular, we extensively discuss the potential of "organ-on-a-chip" devices and their applications in this field. Overall, this review sheds light on the most widely used models and methods, guiding researchers in the rational choice of strategies for studies of microbiota-gut-brain interactions.

Effects of microalgae as dietary supplement on palatability, digestibility, fecal metabolites, and microbiota in healthy dogs

The current trend of dog owners increasingly favoring the functional value of food to assure preventive health and wellbeing of their pets has been raising the interest in microalgae as natural additives with bioactive properties. However, scientific studies addressing the effects of microalgae supplementation in diets for dogs are scarce. This study aimed to evaluate the effects of dietary supplementation with three microalgae species (Chlorella vulgaris, Nannochloropsis oceanica, and Tetradesmus obliquus) on diet palatability, total tract digestibility, metabolizable energy content, fecal metabolites and microbiota of dogs. Twelve adult Beagle dogs were used in three two-bowl tests to compare the palatability of a commercial complete diet for adult dogs without (reference diet) and with 1.5% supplementation of each microalgae. From the results obtained, three digestibility trials were performed according to a replicated Latin square 3 × 3, with six adult Beagle dogs, three experimental periods of 10 days each, and three dietary supplementation levels of microalgae (0.5, 1.0, and 1.5%). In each trial, effects of microalgae supplementation levels on total tract digestibility, metabolizable energy content, fecal metabolites and microbiota of dogs were evaluated. First diet approached or tasted was not significantly affected by microalgae inclusion, but dogs showed a preference for the reference diet over the diets with 1.5% inclusion of C. vulgaris and N. oceanica, no difference being observed with 1.5% T. obliquus. In all digestibility trials, dietary supplementation with microalgae up to 1.5% did not greatly affected the dietary chemical composition and kept unaffected food intake, fecal output and metabolites, and digestibility of nutrients and energy. Compared with the reference diet, supplementation with C. vulgaris increased protein digestibility. Fecal characteristics and metabolites were affected by microalgae supplementation, being the effects dependent on the species. Fecal microbiota composition of dogs fed with microalgae-supplemented diets was modified by promoting the beneficial Turicibacter and Peptococcus genera associated with gut health and activation of the immune system. Overall, the results support C. vulgaris, N. oceanica, and T. obliquus as sustainable functional supplements that potentially enhance gastrointestinal health of dogs through the selective stimulation of microbiota without detrimental effects on food intake and digestibility.

Insect-based diets (house crickets and mulberry silkworm pupae): A comparison of their effects on canine gut microbiota

Background and Aim

The gut microbiome plays an important role in the overall health and well-being of dogs, influencing various physiological processes such as metabolism, nutrient absorption, and immune function. Edible insects are a sustainable and nutritious alternative protein source attracting increasing attention as a potential component of animal feeds, including pet food. However, little is known about the effects of insect-based diets on the gut microbiota of dogs. This study aimed to examine the fecal microbiota of dogs fed a diet that substituted common protein sources (poultry meal) with the house cricket (Acheta domesticus [AD]) or mulberry silkworm pupae (Bombyx mori pupae [BMp]) at different levels.

Materials and Methods

Fifteen healthy adult mixed-breed dogs were systemically randomized and assigned into each block under a completed randomized block design into the following five experimental dietary groups: control diet, 10% AD, 20% AD, 7% BMp, or 14% BMp for 29 days. The amounts fed to the dogs were based on the daily energy requirement. Fecal samples were collected on days 14 and 29 and analyzed for bacterial community structure using 16S ribosomal ribonucleic acid gene sequencing.

Results

At the phylum and genus levels, microbiota and their diversity were generally relatively similar among all treatments. The diets containing insects did not significantly alter the major phyla in the gut microbiome of dogs (p > 0.05). A few significant changes were found in the relative abundance of bacterial genera, with the levels of Allobaculum and Turicibacter being reduced in dogs fed a higher level of BMp. In contrast, only a decrease in Turicibacter was found in dogs fed the lower level of AD than the control diet (p < 0.05). Corynebacterium and Lactobacillus levels in the dogs fed 14% BMp were significantly increased compared with those in the control group (p < 0.05).

Conclusion

These findings suggest that insect-based diets may slightly alter the gut microbiota of dogs. Further research is needed to fully understand the mechanisms by which insect-based diets influence the gut microbiota of dogs and the long-term potential health implications.

The gut microbiota is an emerging target for improving brain health during ageing

The gut microbiota plays crucial roles in maintaining the health and homeostasis of its host throughout lifespan, including through its ability to impact brain function and regulate behaviour during ageing. Studies have shown that there are disparate rates of biologic ageing despite equivalencies in chronologic age, including in the development of neurodegenerative diseases, which suggests that environmental factors may play an important role in determining health outcomes in ageing. Recent evidence demonstrates that the gut microbiota may be a potential novel target to ameliorate symptoms of brain ageing and promote healthy cognition. This review highlights the current knowledge around the relationships between the gut microbiota and host brain ageing, including potential contributions to age-related neurodegenerative diseases. Furthermore, we assess key areas for which gut microbiota-based strategies may present as opportunities for intervention.

Biologia Futura: four questions about ageing and the future of relevant animal models

Understanding how active and healthy ageing can be achieved is one of the most relevant global problems. In this review, I use the "Four questions" framework of Tinbergen to investigate how ageing works, how it might contribute to the survival of species, how it develops during the lifetime of (human) individuals and how it evolved. The focus of ageing research is usually on losses, although trajectories in later life show heterogeneity and many individuals experience healthy ageing. In humans, mild changes in cognition might be a typical part of ageing, but deficits are a sign of pathology. The ageing of the world's populations, and relatedly, the growing number of pathologically ageing people, is one of the major global problems. Animal models can help to understand the intrinsic and extrinsic factors contributing to ageing.

Early life Western diet-induced memory impairments and gut microbiome changes in female rats are long-lasting despite healthy dietary intervention

OBJECTIVE

Western diet consumption during adolescence results in hippocampus (HPC)-dependent memory impairments and gut microbiome dysbiosis. Whether these adverse outcomes persist in adulthood following healthy dietary intervention is unknown. Here we assessed the short- and long-term effects of adolescent consumption of a Western diet enriched with either sugar or both sugar and fat on metabolic outcomes, HPC function, and gut microbiota.

METHODS

Adolescent female rats (PN 26) were fed a standard chow diet (CHOW), chow with access to 11% sugar solution (SUG), or a junk food cafeteria-style diet (CAF) containing various foods high in fat and/or sugar. During adulthood (PN 65+), metabolic outcomes, HPC-dependent memory, and gut microbial populations were evaluated. In a subsequent experiment, these outcomes were evaluated following a 5-week dietary intervention where CAF and SUG groups were maintained on standard chow alone.

RESULTS

Both CAF and SUG groups demonstrated impaired HPC-dependent memory, increased adiposity, and altered gut microbial populations relative to the CHOW group. However, impaired peripheral glucose regulation was only observed in the SUG group. When examined following a healthy dietary intervention in a separate experiment, metabolic dysfunction was not observed in either the CAF or SUG group, whereas HPC-dependent memory impairments were observed in the CAF but not the SUG group. In both groups the composition of the gut microbiota remained distinct from CHOW rats after the dietary intervention.

CONCLUSIONS

While the metabolic impairments associated with adolescent junk food diet consumption are not present in adulthood following dietary intervention, the HPC-dependent memory impairments and the gut microbiome dysbiosis persist.

Two valid and reliable tests for monitoring age-related memory performance and neophobia differences in dogs

The prolonged lifespan of companion dogs has resulted in increased behavioural and physical challenges linked to old age. The development of behavioural tests to identify and monitor age-related differences has begun. However, standardised testing requires validation. The present study aimed to assess external validity, interobserver reliability, and test-retest reliability of an indoor test battery for the rapid assessment of age-related behavioural differences in dogs. Two experimenters tested young dogs (N = 20, mean age ± SD = 2.7 ± 0.4 years) and old dogs (N = 18, mean age ± SD = 11.8 ± 1.3 years) in the test battery once and then again after two weeks. Our results found external validity for two subtests out of six. On both test occasions, old dogs committed more errors than young dogs in a memory subtest and showed more object avoidance when encountering a novel object. Interobserver reliability and test-retest reliability was high. We conclude that the Memory and Novel object subtests are valid and reliable for monitoring age-related memory performance and object neophobic differences in dogs.

Insight into the Fecal Microbiota Signature Associated with Growth Specificity in Korean Jindo Dogs Using 16S rRNA Sequencing

Gut microbiomes are well recognized to serve a variety of roles in health and disease, even though their functions are not yet completely understood. Previous studies have demonstrated that the microbiomes of juvenile and adult dogs have significantly different compositions and characteristics. However, there is still a scarcity of basic microbiome research in dogs. In this study, we aimed to advance our understanding by confirming the difference in fecal microbiome between young and adult dogs by analyzing the feces of 4-month and 16-month-old Jindo dogs, a domestic Korean breed. Microbiome data were generated and examined for the two age groups using 16S rRNA analysis. Comparison results revealed that the 16-month-old group presented a relatively high distribution of Bacteroides, whereas the 4-month-old group presented a comparatively high distribution of the Lactobacillus genus. Microbial function prediction analyses confirmed the relative abundance of lipid metabolism in 4-month-old dogs. In 16-month-old dogs, glucose metabolism was determined using microbial function prediction analyses. This implies that the functional microbiome changes similarly to the latter in adults compared with childhood. Overall, we discovered compositional and functional variations between genes of the gut microbial population in juveniles and adults. These microbial community profiles can be used as references for future research on the microbiome associated with health and development in the canine population.

The effect of age and processing on the in vitro fermentation of fibrous feedstuffs by labrador retriever dogs

Dietary fibre substances in dog foods are composed of cell wall polysaccharides, non-cellulose polysaccharides, and structural non-polysaccharides. The purpose of this study was to determine the effects of dog age and heat-steam pressure (extruding process) on the in vitro fermentation of fibrous feedstuffs (sugar beet pulp, tomato pomace, wheat bran, corn bran, and rice bran) to be included in dog foods. The fibrous feedstuffs were incubated with a fermentation medium mixture and faeces inoculum, which were collected from two 6 month old (puppy), two 2 year old (adult), and two 8 year old (geriatric) dogs. The in vitro cumulative gas production (at 6, 12, 18, 24, 36, and 48 h), true-organic matter disappearance (T-OMd) (at 6, 12, 24, and 48 h), and molarities of short chain fatty acids (SCFA) (acetic, propionic, and butyric acids; AA, PA, and BA) in fermentation fluid (at 24 h) of fibrous feedstuffs were determined. The extruding process increased the in vitro cumulative gas production of rice bran (at 12, 18, 24, and 48 h) and wheat bran (at 6, 12, 24, and 36 h) (P < 0.05). In addition, in vitro cumulative gas production values of tomato pomace (at 12, 18, 24, 36, and 48 h) were reduced by the extruding process (P < 0.05). The extruding process increased the in vitro T-OMd values of sugar beet pulp (at 6, 12, and 24 h), wheat and rice bran (at 6 and 12 h), and the molarities of AA, BA, and total SCFA of the in vitro fermentation fluid of sugar beet pulp and wheat bran (P < 0.05). The in vitro cumulative gas production values of tomato pomace from faecal inoculums of the puppy and adult dogs were higher than that of the geriatric dog (P < 0.05). The in vitro T-OMd of sugar beet pulp (at 48 h) and extruded corn bran (at 6 h) with faecal inoculums of adult dog was higher than those of inoculum from puppy faeces (P < 0.05). The molarity of AA of tomato pomace with adult dog's faecal inoculum was higher than those from puppy and geriatric dog (P < 0.05). The molarities of AA, BA, and total SCFA with corn bran from faeces inoculums of the puppy and adult dog was higher than that of the geriatric dog (P < 0.05). The molarities of AA and total SCFA of the in vitro fermentation fluid of extruded rice bran with faecal inoculums from the geriatric dogs was higher than those with faecal inoculums from the puppy and adult dogs (P < 0.05). As a result, the extruding process positively affected the in vitro fermentation values of sugar beet pulp, wheat bran, and rice bran. Furthermore, the organic acid molarities of the in vitro fermentation fluid of extruded rice bran from the geriatric dog was higher than those from the puppy and adult dogs. Sugar beet pulp, tomato pomace, wheat bran, and corn bran can be used as a source of fibre in food for puppy, adult, and geriatric large dogs.

Canine Fecal Microbiota Transplantation: Current Application and Possible Mechanisms

Fecal microbiota transplantation (FMT) is an emerging therapeutic option for a variety of diseases, and is characterized as the transfer of fecal microorganisms from a healthy donor into the intestinal tract of a diseased recipient. In human clinics, FMT has been used for treating diseases for decades, with promising results. In recent years, veterinary specialists adapted FMT in canine patients; however, compared to humans, canine FMT is more inclined towards research purposes than practical applications in most cases, due to safety concerns. Therefore, in order to facilitate the application of fecal transplant therapy in dogs, in this paper, we review recent applications of FMT in canine clinical treatments, as well as possible mechanisms that are involved in the process of the therapeutic effect of FMT. More research is needed to explore more effective and safer approaches for conducting FMT in dogs.

Recent Advances in Understanding the Structure and Function of the Human Microbiome

Trillions of microbes live within our bodies in a deep symbiotic relationship. Microbial populations vary across body sites, driven by differences in the environment, immunological factors, and interactions between microbial species. Major advances in genome sequencing enable a better understanding of microbiome composition. However, most of the microbial taxa and species of the human microbiome are still unknown. Without revealing the identity of these microbes as a first step, we cannot appreciate their role in human health and diseases. A shift in the microbial balance, termed dysbiosis, is linked to a broad range of diseases from simple colitis and indigestion to cancer and dementia. The last decade has witnessed an explosion in microbiome research that led to a better understanding of the microbiome structure and function. This understanding leads to potential opportunities to develop next-generation microbiome-based drugs and diagnostic biomarkers. However, our understanding is limited given the highly personalized nature of the microbiome and its complex and multidirectional interactions with the host. In this review, we discuss: (1) our current knowledge of microbiome structure and factors that shape the microbial composition, (2) recent associations between microbiome dysbiosis and diseases, and (3) opportunities of new microbiome-based therapeutics. We analyze common themes, promises, gaps, and challenges of the microbiome research.

Mutual Links between the Endocannabinoidome and the Gut Microbiome, with Special Reference to Companion Animals: A Nutritional Viewpoint

There is growing evidence that perturbation of the gut microbiome, known as “dysbiosis”, is associated with the pathogenesis of human and veterinary diseases that are not restricted to the gastrointestinal tract. In this regard, recent studies have demonstrated that dysbiosis is linked to the pathogenesis of central neuroinflammatory disorders, supporting the existence of the so-called microbiome-gut-brain axis. The endocannabinoid system is a recently recognized lipid signaling system and termed endocannabinoidome monitoring a variety of body responses. Accumulating evidence demonstrates that a profound link exists between the gut microbiome and the endocannabinoidome, with mutual interactions controlling intestinal homeostasis, energy metabolism and neuroinflammatory responses during physiological conditions. In the present review, we summarize the latest data on the microbiome-endocannabinoidome mutual link in health and disease, focalizing the attention on gut dysbiosis and/or altered endocannabinoidome tone that may distort the bidirectional crosstalk between these two complex systems, thus leading to gastrointestinal and metabolic diseases (e.g., idiopathic inflammation, chronic enteropathies and obesity) as well as neuroinflammatory disorders (e.g., neuropathic pain and depression). We also briefly discuss the novel possible dietary interventions based not only on probiotics and/or prebiotics, but also, and most importantly, on endocannabinoid-like modulators (e.g., palmitoylethanolamide) for intestinal health and beyond.

Effect of Nutrition on Age-Related Metabolic Markers and the Gut Microbiota in Cats

Age-related changes in the gut microbiota and metabolites are associated with the increased risk of detrimental conditions also seen with age. This study evaluated whether a test food with potential anti-aging benefits results in favorable changes in plasma and fecal metabolites and the fecal microbiota in senior cats. Forty healthy domestic cats aged 8.3–13.5 years were fed a washout food for 30 days, then control or test food for 30 days. After another 30-day washout, cats were switched to the other study food for 30 days. Assessment of plasma and fecal metabolites showed lower levels of metabolites associated with detrimental processes (e.g., uremic toxins) and higher levels of metabolites associated with beneficial processes (e.g., tocopherols) after cats consumed the test food compared with the control food. A shift toward proteolysis with the control food is supported by higher levels of amino acid metabolites and lower levels of carbohydrate metabolites. Operational taxonomic units of greater abundance with the test food positively correlated with carbohydrate and nicotinic acid metabolites, and negatively correlated with uremic toxins, amino acid metabolism, secondary bile salts, and branched-chain fatty acids. Taken together, the test food appears to result in greater levels of metabolites and microbiota associated with a healthier state.

Effects of Zinc Source and Enzyme Addition on the Fecal Microbiota of Dogs

Supplemental zinc from organic sources has been suggested to be more bioavailable than inorganic ones for dog foods. However, the bioavailability of zinc might be affected by dietary constituents such as phytates. The present study aimed to evaluate the effects of two zinc sources (zinc sulfate and zinc proteinate) and the addition of a multi-enzymatic complex from the solid-state fermentation of Aspergillus niger on end-products of fecal fermentation and fecal microbiota of adult Beagles fed a high-phytate diet. The experimental design consisted of three 4 × 4 Latin Squares with a 2 × 2 factorial arrangement of treatments (n = 12 Beagles), with four periods and four diets: zinc sulfate without (IZ) or with (IZ +) enzyme addition, and zinc proteinate without (OZ) or with (OZ +) enzyme addition. Enzyme addition significantly affected Faith’s phylogenetic diversity index, whereas zinc source did not affect either beta or alpha diversity measures. Linear discriminant analysis effect size detected nine taxa as markers for organic zinc, 18 for inorganic source, and none for enzyme addition. However, with the use of a negative binomial generalized linear model, further effects were observed. Organic zinc was associated with a significantly higher abundance of Firmicutes and lower Proteobacteria and Bacteroidetes, although at a genus level, the response varied. The DNA abundance of Clostridium cluster I, Clostridium cluster XIV, Campylobacter spp., Ruminococcaceae, Turicibacter, and Blautia was significantly higher in dogs fed IZ and IZ + diets. Higher abundance of genus Lactobacillus was observed in dogs fed enzyme-supplemented diets. End-products of fecal fermentation were not affected by zinc source or enzymes. An increase in some taxa of the phyla Actinobacteria and Firmicutes was observed in feces of dogs fed organic zinc with enzyme addition but not with inorganic zinc. This study fills a gap in knowledge regarding the effect of zinc source and enzyme addition on the fecal microbiota of dogs. An association of zinc bioavailability and bacteria abundance is suggested, but the implications for the host (dog) are not clear. Further studies are required to unveil the effects of the interaction between zinc sources and enzyme addition on the fecal microbial community.

Dogs' Microbiome From Tip to Toe

Microbiota and microbiome, which refers, respectively, to the microorganisms and conjoint of microorganisms and genes are known to live in symbiosis with hosts, being implicated in health and disease. The advancements and cost reduction associated with high-throughput sequencing techniques have allowed expanding the knowledge of microbial communities in several species, including dogs. Throughout their body, dogs harbor distinct microbial communities according to the location (e.g., skin, ear canal, conjunctiva, respiratory tract, genitourinary tract, gut), which have been a target of study mostly in the last couple of years. Although there might be a core microbiota for different body sites, shared by dogs, it is likely influenced by intrinsic factors such as age, breed, and sex, but also by extrinsic factors such as the environment (e.g., lifestyle, urban vs rural), and diet. It starts to become clear that some medical conditions are mediated by alterations in microbiota namely dysbiosis. Moreover, understanding microbial colonization and function can be used to prevent medical conditions, for instance, modulation of gut microbiota of puppies is more effective to ensure a healthy gut than interventions in adults. This paper gathers current knowledge of dogs' microbial communities, exploring their function, implications in the development of diseases, and potential interactions among communities while providing hints for further research.

Age and Giardia intestinalis Infection Impact Canine Gut Microbiota

Giardia intestinalis is a flagellated protozoan responsible for giardiosis (also called giardiasis in humans), the most prevalent and widespread parasitic infection in humans and mammals worldwide. The intestinal microbiota is highly diverse and any alteration in its composition may impact on the health of the host. While studies on the mouse model of giardiosis described the role of the gut microbiota in host susceptibility to infection by the parasite, little is known about the gut microbiota during natural infections in dogs and particularly in puppies. In this study, we monitored naturally G. intestinalis-infected puppies for 3 months and quantified cyst excretion every 2 weeks. All puppies remained subclinically infected during the sampling period as confirmed by fecal examination. In parallel, we performed 16S Illumina sequencing of fecal samples from the different time points to assess the impact of G. intestinalis infection on gut microbiota development of the puppies, as well as gut health markers of immunity such as fecal IgA and calprotectin. Sequencing results revealed that the canine fecal microbiota of Giardia-infected puppies becomes more complex and less diverse with increasing age. In addition, significant differences in the structure of the microbiota were observed between puppies with high and low Giardia cyst excretion. Chronic subclinical G. intestinalis infection appears to be associated with some detrimental structural changes in the gut microbiota. G. intestinalis-associated dysbiosis is characterized by an enrichment of facultative anaerobic, mucus-degrading, pro-inflammatory species and opportunistic pathogens, as well as a reduction of Lactobacillus johnsonii at specific time points. Calprotectin levels increased with age, suggesting the establishment of chronic low-grade inflammation in puppies. Further work is needed to demonstrate whether these alterations in the canine gut microbiota could lead to a dysbiosis-related disease, such as irritable bowel syndrome (IBS) or inflammatory bowel disease (IBD).