In the early 1900s Metchnikoff found that bulgarians eating yoghurt had
longer lifespans than did others. Since that time a number of
investigators have examined the beneficial effects of lactic acid
bacteria on intestinal function. It is thought that these "probiotics"
improve intestinal conditions by speeding the return of "normal flora".
The mode of action may be a number of things ranging from the drop in pH
associated with lactic acid bacterial growth which is inhibitory to many
harmful bacteria, to colonization of the yoghurt bacteria in the
intestines and preventing or displacing the colonization of pathogens.
Certain lactic acid bacteria do a better job than others and the current
rage in human yoghurt is bifidobacteria in the yoghurt. Early work and
more current work by the Japanese finds an association between
bifidobacteria and animal health.
If you look at some of Iams product literature, they use
Fructooligosaccharides in their feed because of this sugars' ability to
"feed" bifidobacteria and other lactic bacteria in the intestine. For
more information on this you might look at Am. J. Vet. Res. Vol.