Paws, claws, and microbes



The hidden world of pet microbiomes

Sponsored by Hill's Pet Nutrition

The study of the microbiome in veterinary science has become a critical area of research, with significant implications for the health management of companion animals such as cats and dogs. The microbiome, a complex consortium of commensal, symbiotic, and pathogenic microorganisms, includes bacteria, archaea, fungi, viruses, and protozoa.1 These microbial communities are found across various niches in the animal host, including the gastrointestinal tract, skin, oral cavity, respiratory system, and urogenital tract. Comprised of 1010 to 1014 microorganisms and at least 20 million unique microbial genes, the microbiome is the largest genetic component of the human or animal superorganism.1

A diverse and balanced microbiome is crucial for health. However, dysbiosis, or the imbalance in the microbial community structure, is linked to gastrointestinal issues like inflammatory bowel disease (IBD), as well as systemic conditions including obesity and diabetes. This positions the microbiome to be a key focus for diagnostic and therapeutic research into intestinal, skin, oral, respiratory, and urogenital health in companion animals.

In the realm of animal health, the gastrointestinal microbiome has been the most extensively characterized. The microbiome of companion animals is predominantly composed of bacterial phyla, with Fusobacteria, Firmicutes and Bacteroidetes being the most abundant, followed by Proteobacteria and Actinobacteria.2-5 These microbes engage in a myriad of biochemical pathways that are crucial for host physiology, including the fermentation of indigestible dietary polysaccharides, production of short-chain fatty acids (SCFAs) like butyrate, propionate and acetate, as well as the synthesis of essential vitamins and amino acids. These microbial metabolites are vital for proper functioning of multiple organ systems and overall health and wellness.

The gut microbiome also plays a pivotal role in the development and function of the host immune system, protecting the host from pathogens, helping the intestinal barrier function and providing beneficial metabolites.6 The composition of the intestinal microbiome is influenced by diet, stress, drug therapies such as antibiotics or nonsteroidal anti-inflammatory drugs (NSAIDs), inflammation of the intestinal tract and the structure of the intestine to name a few.7,8 Microbial metabolites of the gut microbiome provide multiple benefits for intestinal health as well as distant organ systems, such as the kidneys, brain and heart.

The cutaneous microbiome of cats and dogs is equally complex, with distinct microbial populations occupying various skin niches influenced by factors such as sebaceous gland density and moisture content.9 The skin microbiota contributes to the protective barrier against pathogenic invasion and modulates local immune responses. Dysbiosis of the skin microbiota has been associated with dermatological conditions such as atopic dermatitis, where alterations in microbial diversity and the proliferation of opportunistic pathogens like Staphylococcus spp. can exacerbate skin inflammation.10

The oral microbiome of companion animals is a diverse microbial ecosystem which can be protective and provide essential barriers and interactions with the host immune system, or pathogenic and cause diseases. It is also a significant contributor to oral health, with an imbalance in this community is associated with periodontal disease, which can have systemic health implications.11 Because the oral microbiome can be altered by many factors, including age, food consumption, health condition and environmental changes, the oral microbiota provides a potential diagnostic tool and therapeutic target for preventing periodontitis and its associated comorbidities.

While the respiratory, urogenital, and otic microbiomes are less well-characterized, they are recognized for their roles in local defense mechanisms and potential implications for systemic health. For example, the respiratory microbiome may influence susceptibility to respiratory pathogens,12 and the urogenital microbiome has been associated with urinary tract infections and reproductive health.13 Research to further characterize and define the role the local microbiomes play in each of these organ systems is ongoing.

Advancements in high-throughput sequencing technologies and bioinformatics have allowed for in-depth analysis of the pet microbiome, providing insights into not only its composition, but also its functional potential. Metagenomic and metatranscriptomic approaches enable the identification of microbial genes and their expression profiles, shedding light on the metabolic activities within these communities and their interactions with the host.

The microbiome is a fundamental component of feline and canine health, with extensive implications for therapeutic interventions. As veterinary healthcare professionals, learning about the microbiome and its interactions with the host is helpful for the development of targeted treatments and preventive measures that support the overall health and well-being of companion animals. That is why our goal at Hill’s Pet Nutrition is to conduct groundbreaking microbiome research to learn how to develop products that feed and nourish pets and their unique microbiomes, and share this knowledge with fellow researchers, pet parents and veterinary health care team members.



Benefits of products

Utilization of otherwise inaccessible nutrients and energy from the diet

Production of short-chain fatty acids (SCFAs; acetate, propionate, butyrate)14

Release and metabolism of fiber-bound plant polyphenols15

Acetate and propionate are energy substrates for microbial growth but are also absorbed from the colon and provide sources of energy for the body. Butyrate is an important energy fuel for colonocytes. SCFAs facilitate the absorption of sodium and water in the colon.

Polyphenols are molecules from fruits and vegetables with antioxidant and anti-inflammatory properties.

Synthesis of vitamins

Microbial synthesis of vitamin K and water soluble B vitamins16 

Vitamin K is a fat soluble vitamin involved in blood coagulation and in binding calcium in growing bones.

B vitamins (biotin, cobalamin, folate, niacin, pantothenate, pyridoxine, riboflavin and thiamin) are a class of water-soluble vitamins that play important roles in cell metabolism and help the body to utilize energy from food.

Development and activity of the immune system

Intestinal bacteria present early in life are necessary to establish oral tolerance to commensal bacteria and food antigens17, 18

In healthy animals, the microbiota and the immune system maintain a balance so that excessive immune and inflammatory responses are avoided.

Protection against harmful microbial species

The gut microbiota induce the gut immune system to produce Immunoglobulin A ( IgA)19

The microbiota stimulate intestinal secretory cells to produce antimicrobial compounds (beta-defensins, cathelicidins, bactericidal/permeability-increasing protein and chemokines)21, 22

Beneficial bacteria competitively exclude pathogens by occupying receptor sites, competing for space and nutrients23

Ig A limits local epithelial bacterial colonization and prevents penetration of bacteria through the epithelial layer. The secreted antimicrobial peptides are retained in the mucus layer, which provides a physical and antibacterial barrier while allowing the presence of luminal microbiota20

Improved integrity of the mechanical mucosal barrier

The microbiota stimulates the mucus layer24 and alters the mucin chemical composition25

Mucins (highly glycosylated macromolecules) form the first barrier between the gut contents and epithelial cells, protecting them from direct contact with commensal bacteria and their components, such as lipopolysaccharide, peptidoglycans, superantigens and bacterial DNA to name a few.


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