By Dr. Sarah Dodd BVSc, MSc
The gastrointestinal (GI) tract, commonly referred to as the gut, is a complex organ system on which every living animal relies. In essence, the GI tract can be thought of as an interface through which the exterior environment interacts with the animal, though in reality the tract bears its own complex ecosystem.
Within the GI tract, ingested items are broken down, nutrients and pharmaceuticals are absorbed, and toxins are excreted. Additionally, the gut acts as a defense against the external environment, protecting the animal from invasion by pathogens and noxious substances.1 In part, this activity is regulated by the animal, the other part regulated by the extensive microbial community existing within the gut.2 Indeed, there are more microbial cells contained within the GI tract than somatic cells within an animal’s body.3
Overall Health Starts in the GI Tract
A healthy GI tract is paramount for systemic health. The front-line workers are the enterocytes that make up the brush border forming the boundary between the lumen of the gut and the lymphatics and blood vessels transporting absorbed substances from the gut to the portal vein and eventually to systemic circulation. Gastrointestinal disturbances can have sudden and obvious outcomes, such as occasional vomiting and diarrhea, or more long-term effects, far reaching and subtle effects. The gut is intrinsically linked with a number of different body systems, through which manipulation, disease and therapy can all occur.
When considering gut health, there are a number of individual but related factors to consider. Nutrients can be added to support enterocyte health, modulate inflammation within the gut and support or even directly manipulate the microbial community. Different approaches are required for different situations or conditions.
Though the splanchnic blood flow accounts for over 20% of all the circulating blood volume in the dog 4, the enterocytes lining the gut derive much of their nutrition directly from the nutrients within the gut. One key nutrient is glutamine, a dispensable amino acid some consider to be conditionally essential for the gut. It serves an important role in protein and nucleic acid synthesis, but most importantly for the enterocytes, it can be metabolized as a primary energy source.5
Nutritional Support for Gut Health
Natural food-derived or nutraceutical supplements may be added to an animal’s diet to reduce inflammation. These include antioxidant vitamin E, immunomodulatory zinc, and omega-3 fatty acids eicosapentaenoic acid and docosahexaenoic acid.6 Additionally, a number of plants containing specific beneficial phytochemicals, such as turmeric and green tea extract, have also demonstrated local anti-inflammatory effects within the gut. These can be utilized to reduce inflammation when disease processes are active or can be used in a protective capacity.
The environment within the gut is a complex milieu of digesta, indigestible materials, secretions and products from the gut microbiota and exocrine secretions from the GI tract and associated organs. This microenvironment is host to an incredibly diverse and abundant population of bacteria, fungi, archaea and other numerous microorganisms.2, 3
Certain functional foods may support stable populations of beneficial microbiota while inhibiting the growth of unwanted microorganisms these are termed ‘prebiotics’. Prebiotics are typically indigestible but soluble fibers that bacteria within the gut can ferment as an energy source. In turn, these bacteria excrete compounds such as short-chain fatty acids that nourish the cells lining the gut.7 These beneficial bacteria may also be added directly to the gut in the form of probiotics – stabilized viable colony forming units of specific strains of bacteria. When prebiotics and probiotics are provided together they are termed synbiotics.
The GI tract is a complex and critical system providing nourishment for every other cell in the body, preventing infection and excreting noxious substances. Supporting the health of the GI tract thus supports systemic health and can play a critical role in prevention and maintenance of a plethora of health conditions.
Dr. Sarah Dodd earned her veterinary degree at Massey University in New Zealand. After graduation, Dr. Dodd completed a specialty nutrition internship and MSc degree at the Ontario Veterinary College, and then progressed into a veterinary and comparative nutrition residency and PhD. Presently, she is in the second year of both her residency and PhD programs. Dr. Dodd’s research focuses on the suitability of plant-based diets for companion animals, and she enjoys teaching clients and students about the pros and cons of unconventional diets for dogs and cats.
- Jergens, A., Understanding gastrointestinal inflammation — implications for therapy. Journal of Feline Medicine and Surgery, 2002. 4: p. 179-182.
- Suchodolski, J., Microbes and gastrointestinal health of dogs and cats. Journal of Animal Science, 2011. 89: p. 1520-1530.
- Costa, M. and J. Weese, Understanding the intestinal microbiome in health and disease. Veterinary Clinics of North America: Equine, 2018. 34: p. 1-12.
- Johnstone, F., Measurement of splanchnic blood volume in dogs. American Journal of Physiology, 1956. 185(3): p. 450-452.
- Wang, B., et al., Glutamine and intestinal barrier function. Amino Acids, 2015. 47: p. 2143-2154.
- Bobeck, E., Functional nutrition in livestock and companion animals to modulate the immune response. Journal of Animal Science, 2020. 98(3): p. 1-8.
- Gagné, J., et al., Effects of a synbiotic on fecal quality, short-chain fatty acid concentrations, and the microbiome of healthy sled dogs. BMC Veterinary Research, 2013. 9(246).