The Gut as an Ecosystem
Unfortunately, not all animals remain healthy throughout their lives. Accident, disease and often surgical or medical intervention will be necessary. In almost all cases, modification of the diet will assist recovery, slow the progression of incurable disease or improve the effect of organ dysfunction.
In some cases, adjustment of the quantities and proportions of nutrients is sufficient to improve your fur kids’ health. In others, a more complex manipulation is required when we need to consider not just a particular nutrient but a particular type of that nutrient and its effect on the whole body. To understand this, we need to take an overall view and realize that the digestive tract is not just a conveyor belt through the body, but is actually a complete ecosystem.
By definition, an ecosystem has two components – a community of organisms (the biotic component), and their habitat [Bacteria in the Gut: Friends and Foes and How to Alter the Balance] [ref]. The organisms interact with each other, often competing for space and food. They are also influenced by chemical and physical features of their environment (the abiotic component). The biotic component in the gut is formed of bacteria, fungi, protozoa, yeast and other organisms. Their numbers vary in different sections of the digestive tract, tending to increase in numbers distally (situated farthest from the middle and front of the jaw, as a tooth or tooth surface). The acidity of the stomach prevents high numbers there and rapid transit of food through the upper regions of the bowel normally discourages proliferation of organisms. However, in the large intestine, and in particular in the colon, high numbers of micro-organisms flourish [Ref]. They are able to do so because the food residues are present in greater quantity and the flow rate is slower. Their effect on the body of the host animal is therefore greatest in the colon.
It’s not a question of just one or two or three species; rather, it’s about how they are interacting and influencing complex, community-wide changes. It is the habitat that determines what microbes can survive. This is why you don’t have the same microbes on your skin or your mouth as you do in your gut. The environment of the gut naturally selects for the microbes that thrive in that habitat. So why don’t we all have the same gut microbiome? Several factors, including our genetics, diets, lifestyles, geographical location, and environmental exposures can all influence community dynamics by causing slight variations in the gut habitat from one person to the next. In fact, there is no one “healthy” microbiome, and even a single individual will show some change over time.
The composition of the gut flora is established within 2 to 3 weeks of birth (some research suggest it might be much later, between week 8 and 12) through contact with the mother and her environment. Once organisms colonize the gut, they are generally there for life. Their relative proportions can be influenced by the diet of your fur kid. Most of the research into the biotic component of the gastrointestinal ecosystem has concerned bacteria, the function and importance of the other micro-organisms being, as yet, not fully understood.
The intestinal microbiota comprises viruses, bacteria, fungi, and protozoa. In the past, the word microflora has been used to describe this complex ecosystem, but microbiota (from –bios, “living organisms”) is the more appropriate term. The microbiome is the collective genome of all these microbes. Most studies to date have focused on the bacterial microbiota, which is estimated to make up the vast majority of the intestinal microbiota.
Gut bacteria fall into three groups – the good, the bad and the indifferent. To put this more scientifically, the beneficial species (bifidobacteria and eubacteria together with lactobacilli and other lactic acid bacterial), the pathogenic and putrefactive species (enterobacteria and clostridia) and neutral species (effectively the rest). These bacteria are part of the ecosystem, interacting with each other and the environment, but chiefly living their own lives and producing their own waste. This waste may be of use to the host animal, e.g. short-chain fatty acids which are used as a source for energy by the cells lining the colon, or may damage the host, e.g. toxic or carcinogenic products. If the beneficial bacteria can be increased in numbers, then the beneficial effect on the host will be greater. Greater numbers of these will also tend to crowd out the pathogens. This process is known as exclusion by competition. In doing so, it will reduce the harmful effects in the host. It is also possible that the beneficial bacteria may produce substances toxic to the pathogens and that beneficial bacteria boost the body’s ability to resist potential toxic effect of pathogens.
Did you Know? An estimated 100 trillion microbial cells are present within the intestine, up to 10 times the number of mammalian cells in the whole body. Combined, microbial genes outnumber host genes by an estimated factor of 10.
This complex ecosystem of gut bacteria has a tremendous influence on the health of your fur kids. The interactions between bacteria and host are mediated through direct contact between microbes and the immune system and through various microbiota-derived metabolites. A physiologic microbiome modulates the immune system, protects against enteropathogens, and provides nutritional benefits to your fur kids.
Protecting or Restoring the Ecosystem
Think of yourself as a park ranger, responsible for maintaining the health of a rainforest. You’d probably keep a close eye on any invasive species. You’d also want to ensure the health of native species by making sure they had the foods and other resources they need to survive. You might even track the stability of the ecosystem over time. This is called conservation ecology.
If the forest is ravaged by a disturbance, you might help restore it by taking more drastic measures, such as providing certain nutrients to the ecosystem, removing invasive species, and reseeding it with native species. This is called restoration ecology. The restored ecosystem might not look exactly the same as it did before, but in many cases, it is healthy and can serve the same functions.
Now think of yourself as a park ranger for your gut ecosystem. If you have a relatively healthy gut microbiota, you’d want to continue to support the beneficial microbes with nutrients, and inhibit the growth of pathogenic microbes by limiting their food sources. In this way, you would increase the resilience of the ecosystem to any minor disturbances. Of course, you’d still want to avoid any major disturbances, like antibiotics or parasitic infections.
Unfortunately, many other aspects throughout life can hinder the growth and stabilization of a diverse microbiome (your forest), creating an imbalance known as dysbiosis. A variety of behaviors have been linked to dysbiosis, such as:
- Use of antibiotics
- Oversanitation, such as the use of triclosan-based antimicrobial hand soap
- Toxic exposure: pesticides, smoking
- Low fibre diet
- High sugar diet
- Lack of breastfeeding
It is possible to manipulate these bacterial populations in two ways:
- Provide beneficial bacteria as a dietary supplement – also known as probiotics
- Provide substrates to encourage increase of beneficial bacteria – also known as prebiotics
Because the microbiota is implicated in the pathophysiology of chronic GI disease, we subscribe to the concept that addition of probiotic and prebiotic therapy may be appropriate. Probiotics are live microorganisms that, when administered in sufficient quantities, is beneficial to your pets. Unfortunately, few studies have evaluated the benefits of probiotics in acute and chronic GI disease. Available research suggest that probiotics have only a minor effect on the intestinal microbiota, but their beneficial effect in dogs with inflammatory bowel disease may be due in part to immune stimulation and / or enhancement of intestinal barrier function. It appears that administration of higher doses and multiple strains leads to a higher probability that probiotic bacteria will be able to colonize the gut.
Prebiotics are fermentable and nonfermentable fibers that, after reaching the large intestine, are metabolized by intestinal bacteria to produce SCFA and other metabolites that may be immunomodulatory.
Even though tremendous progress has been made in the last decades to clarify the mechanisms of intestinal homeostasis, dysbiosis and disease, we are only at the beginning of understanding the complexity of the gut ecosystem or microbiota and the underlying interaction networks for pets and parents alike.
References and Research
There is a very large body of research available today to pursue. Below are a select few we found interesting.
- Understanding the Canine Intestinal Microbiota and Its modification by pro-. pre- and synbiotics - what is the evidence? [Ref], [PubMED]
- Intestinal microbiota of dogs and cats: a bigger world than we thought. [PubMED]
- Pathogens, microbiome and the host: emergence of the ecological Koch's postulates [Oxford]
- Studying microbial functionality within the gut ecosystem by systems biology [BMC] [PubMed]
- Rebuilding the Gut Microbiota Ecosystem [PubMED]
- Linking the Gut Microbial Ecosystem with the Environment: Does Gut Health Depend on Where We Live? [Frontiers]
- Dietary polysaccharides: fermentation potentials of a primitive gut ecosystem [Wiley]
- How the microbial ecosystem inside our gut influences health and disease [UniLuxembourg]