Page 77 - Small Animal Clinical Nutrition 5th Edition

Macronutrients 77

and/or activity in the GI flora that confers well being and health Table 5-7. Probiotic benefits and potential mechanisms.
VetBooks.ir benefits to the host (Gibson, 2004). A prebiotic index (PI) may Benefit Proposed mechanism
be used to quantify prebiotic effects in vitro (Palframan et al,
Modulation of the cytokine profile
Anti-allergy
2003). The PI is based on changes in key bacterial groups dur-
ing fermentation of prebiotic fibers with fecal material in batch Anticarcinogenic Metabolism and deactivation of
carcinogens
cultures and is defined by the following equation: Anti-diarrheal Immunomodulation/stimulation of GI
immune system, competitive exclusion,
production of antimicrobials
PI = (Bifidobacteria total) - (Bacteroides total) + (Lactobacillus Antiinflammatory Stimulation of the antiinflammatory
total) - (Clostridia total). cytokine IL10
Cholesterol synthesis Hydrolysis of bile salts, increased
fermentation of end products
The above equation defines the total bacterial count in the Immunomodulation Stimulation of the Th1 cytokine profile to
culture. A larger PI indicates that the prebiotic fiber can down regulate allergic responses
increase numbers of beneficial bacterial species (bifidobacteria
and Lactobacillus spp.) at the expense of pathogenic or less
desirable bacterial species (Bacteroides and Clostridium spp.). spp. readily ferment FOS, which enhances bacterial growth rate
The mechanism by which prebiotics are selectively ferment- (Gibson and Roberfroid, 1995; Roberfroid et al, 1993; Hidaka
ed by specific bacteria is not well understood. Two potential et al, 1986; Bunce et al, 1995). Increased numbers of these bac-
mechanisms have been proposed: 1) the presence of an exo-gly- terial species may benefit the overall health of people and other
cosidase enables bacteria to metabolize the prebiotic fiber and animals, including pigs, rabbits and rats (Bunce et al, 1995;
2) an uptake mechanism exists on the cell walls of specific bac- Willard et al, 1994; Howard et al, 1995; Buddington et al,
teria for intact oligosaccharides (Rastall et al, 2005). 2002).
Prebiotics traditional target beneficial bacteria such as bifi- Data from canine feeding studies, however, are sparse and
dobacteria and Lactobacillus spp. However, the desirable bene- results have been mixed. Some studies showed trends towards
fits of butyrate production for the colon is recognized increas- increased bifidobacteria with FOS supplementation whereas
ingly; thus, the potential for targeting non-clostridial butyrate others showed no response (Swanson, 2002, 2002a; Flickinger,
producers such as gut eubacteria (Rastall et al, 2005). Prebiotic 2000; Strickling et al, 2000). In a study using chicory (a source
fibers are also thought to reduce fecal odor by modifying fecal of inulin), there were no significant differences in the level of
concentration of metabolites and improve immune function by fecal bifidobacteria when dogs were fed dry, extruded food
influencing gut-associated immune cells. made with either 3% chicory (a non-digestible oligosaccharide)
or 3% glucose, although there was a significant increase in
TYPES OF PREBIOTIC FIBERS clostridial numbers when foods with higher protein level were
Substances that may have prebiotic activity are mainly fed (Zentek et al, 2003).
oligosaccharides such as mannanoligosaccharide (MOS), fruc- There are even fewer feline studies and not much informa-
tooligosaccharide (FOS), galactooligosaccharide (GOS), tion is available currently. Arabinogalactan, another prebiotic
xylooligosaccharide (XOS), isomaltooligosaccharide (IMOS), polysaccharide from the Western larch tree, increased lacto-
soybean oligosaccharides (SOS), pectic oligosaccharides, chi- bacilli in dogs (Grieshop et al, 2002). Although studies in peo-
tooligosaccharide, lactusucrose and lactulose or other polysac- ple and other species (e.g., rats and pigs) showed that prebiotics
charide/oligosaccharide-containing sources such as inulin, RS benefit GI health by promoting a healthy gut flora, it is evident
and arabinogalactans (Floch and Hong-Curtiss, 2002;Topping that there is much that needs to be determined about the effi-
et al, 2003; Gibson et al, 2005). Many of these prebiotics, par- cacy of different prebiotics in dogs and cats and the appropri-
ticularly oligosaccharides, occur naturally in foods such as arti- ate doses. Prebiotic doses that have been tested with no delete-
chokes, onions, bananas, wheat bran and chicory (Hussein et al, rious effects range from 0.5 to 3 g/day and 0.5 to 2% of the food
1998). Oligosaccharides are polymers that contain up to nine on a DM basis. New and emerging prebiotics that still need to
sugars. Using the PI (Palframan et al, 2003), lactulose, IMOS, be studied in companion animals include GOS, IMOS, SOS
SOS and GOS provide significantly better prebiotic activity and XOS. In addition, it would be advantageous to combine
than FOS. An in vitro fermentation study comparing different the effect of prebiotic fibers and the appropriate traditional
oligosaccharides showed that XOS and lactulose produced the function of fibers to obtain the best combination for improving
largest increase in bifidobacteria, whereas GOS produced the gut flora and stool characteristics.
largest decrease in clostridia (Rycroft et al, 2001). All the pre-
biotics tested, including FOS, inulin, IMOS and SOS, GUT MICROFLORA
increased bifidobacteria and most decreased clostridia. Many studies have emerged recently about the importance of
Although these studies show that many prebiotics are poten- gut flora to GI health in particular and immune function health
tially useful, more feeding studies need to prove their utility in in general. The gut flora and mucosa act as barriers against
vivo. FOS is the most extensively studied prebiotic and has invasion by gut pathogens.The gut flora also plays a significant
been shown to stimulate growth of bifidobacteria in in vivo and role in modifying metabolic end products of food, detoxifying
in vitro studies. In the colon, bifidobacteria and Lactobacillus toxins in the body and competing for nutrients and coloniza-