Probiotics are live microorganisms that when administered in adequate amounts confer a health effect on the host.1 There have been many studies of the effects of probiotics on the health of people, but very few in small animals. In a recent
review of human studies involving probiotics, it was stated that "well-established probiotic effects include:2
1. Prevention and/or reduction of duration and complaints of rotavirus-induced or antibiotic-associated diarrhea as well as
alleviation of complaints due to lactose intolerance;
2. Reduction of the concentration of cancer-promoting enzymes and/or putrefactive (bacterial) metabolites in the gut;
3. Prevention and alleviation of unspecific and irregular complaints of the gastrointestinal tracts in healthy people;
4. Beneficial effects on microbial aberrancies, inflammation, and other complaints in connection with inflammatory diseases
of the gastrointestinal tract, Helicobacter pylori infection, or bacterial overgrowth;
5. Normalization of passing stool and stool consistency in subjects suffering from obstipation or an irritable colon;
6. Prevention or alleviation of allergies and atopic diseases in infants; and
7. Prevention of respiratory tract infections (common cold, influenza) and other infectious diseases as well as treatment
of urogenital infections."
Infectious diseases are very common in small animals, so the potential beneficial effects of probiotics could impact veterinary
practice significantly. All mechanisms of immune modulation have not been characterized and it is likely these effects vary
by the probiotic. It is known that many probiotics in the lactic acid bacteria group help balance the endogenous microbiota
and some can inhibit replication of pathogenic bacteria. The proposed mechanisms of action include competition for essential
nutrients or receptor sites, binding with pathogenic bacteria, and production of inhibitory substances. It is also now known
that some probiotics can beneficially influence innate and acquired immunity by a variety of proposed mechanisms including
inducing cytokine production, natural killer cell activity, and both specific and nonspecific immunoglobulin production.2
Several recent review articles in human medicine suggest that the evidence to support the theory that probiotics are beneficial
in a variety of human conditions, such as Clostridium
difficile diarrhea and hospital-acquired pneumonia, is minimal and that larger, more rigorously controlled multicenter studies should
be performed.3-5 These findings emphasize that biological effects of individual probiotics will vary and that each probiotic introduced should
be rigorously evaluated in a controlled fashion to define the potential for clinical utility. In addition, the source of the
probiotic should also be considered. For example, in a recent study in Canada, the majority of diets claiming to contain probiotics
generally did not meet the label claim when evaluated.6
