Prebiotics, probiotics and synbiotics (Proceedings)

The gastrointestinal (GI) tract in dogs and cats is a very dynamic organ that performs numerous functions essential for health and well-being. Critical roles of the GI tract include digestion and absorption of nutrients, as well as elimination of potentially harmful substances and waste products. In addition, the GI tract is the most voluminous immunologic organ in the body and also functions as an endocrine organ.

The GI tract also contains a very large and diverse population of bacteria, and these bacteria affect the health of the host in many significant ways. Recognition that these bacteria play a large role in the overall health of the animal has led to research efforts focusing on methods to manipulate the GI bacterial population to improve health.

What are prebiotics?

Prebiotics are defined as nondigestible food ingredients that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of beneficial bacteria in the colon that improve host health. The most common prebiotic found in diets of dogs and cats is dietary fiber.

What are probiotics?

Probiotics are defined as live bacterial preparations that provide clinical health benefits to the host. Probiotics have been used for many years in animal husbandry and have been demonstrated to be effective at improving gastrointestinal health. However, in the case of companion animals, in particular, dogs and cats, few studies have documented the health benefits of probiotics.

Companion animals have extensive gastrointestinal bacterial ecosystems. For example, the mammalian digestive system contains more than 500 different species of bacteria and comprises approximately 95% of the cells in the gastrointestinal tract. Enteric bacteria contribute significantly to the host's resistance to infectious disease. Furthermore, changes in the composition of the intestinal flora can be associated with disease and may, in some cases, be a precipitating factor.

Intestinal microflora are established at birth as the neonate passes through the birth canal and after birth through suckling. Microflora continue to populate the gastrointestinal tract during early development. The most common bacteria with potential to enhance health in pets are the bifidobacteria and lactobacilli. With advancing age, the levels and diversity of these beneficial bacteria begin to decline.

The mechanisms by which probiotics benefit the host are not completely understood, but may involve immune-enhancing and anti-inflammatory activities, modifications to intestinal pH, suppression of pathogenic bacteria through production of inhibitory substances, and competition with pathogens for nutrients and mucosal attachment sites. Bacteria in the gut may also influence the number and distribution of cell types in the gut-associated lymphoid tissue and modulate immune response. It is through a combination of these activities that the full range of probiotic benefits is achieved.

It is now recognized that the effects of these organisms extend well beyond the gastrointestinal tract. With increasing research it is becoming clear that there are differences among various probiotic strains with respect to the types of benefits they are capable of providing. The range and depth of benefits of a probiotic can be species- and strain-specific. Different strains of the same species have been noted to differ in a number of ways, including stability, ability to colonize the GI tract, expression of enzymes and production of inhibitory substances, and perhaps most importantly, clinical efficacy.

New research is demonstrating probiotics can positively affect gastrointestinal conditions and skin function in dogs, and is only beginning to define the possible uses of probiotics in maintenance of companion animal health. It is known the microbial flora of the gut play a role in the normal function and maintenance of health of the gastrointestinal tract. Recent studies have shown the feeding of probiotics to dogs improves stool quality. In one study, young dogs (14 to 16 months old) were fed a probiotic (canine-derived bifidobacteria) or placebo prior to traveling to a training kennel. Fewer dogs who received the probiotic experienced loose stools during the transition to the kennel compared with dogs who received placebo. Another study examined the effects of feeding probiotics to dogs with diarrhea. The time to resolution of diarrhea was approximately 40% less in dogs who received the probiotic. These studies indicate that feeding this organism may promote gastrointestinal tract health in dogs, even in the setting of acute diarrhea. Probiotics also have a beneficial effect on skin health. A randomized, placebo-controlled study in dogs found that transepidermal water loss, a measure of barrier function, was significantly reduced in dogs that received the probiotic compared with dogs that received placebo.

The microbial inhabitants of the gastrointestinal tract are recognized to have a substantial role in the health of animals and their role appears to extend beyond the gastrointestinal tract. Many of the extra-gastrointestinal effects appear to be related to changes in the immune system. Supplementation with probiotic organisms has the potential to provide benefit to animals with a wide range of conditions, and research will continue in animals to further define the optimal uses of these organisms.