Probiotic feed additives - effectiveness and expected modes of action

In animal nutrition, probiotics are viable microorganisms used as a feed supplement, which lead to beneficial effects for the host animal. For most species a trend towards improved performance has been reported due to the use of probiotics, but statistically significant improvements of weight gain and of feed conversion are rare, mainly because of variations in the individual reactions of the ani mals. However, reductions of the incidence of diarrhoea were significant in most studies with piglets and calves. In contrast to human nutrition, where Lactobacillus species are common probiotic pro ducts, in animal nutrition Enterococcus spp., Saccharomyces yeast, and spore-forming Bacillus spp. are most frequently used as probiotic microorganisms. Furthermore, in human nutrition long-term effects for lasting health promotion and longevity are sought, but the aims of probiotic supplementa tion in modern animal production are fast effects such as improvement of weight gain and feed conversion. Thus, results from probiotic research in the field of human nutrition are not completely valid for animal nutrition.