The non-therapeutic use of antibiotics may be reduced by administering both microbial cultures and molecules such as oligosaccharides and lectins. In the former case, an attempt is made at preventing intestinal pathogens from settling down, by administering microorganisms which can colonize the digestive tract and leave out all dangerous bacteria. The microorganisms mostly used in connection with monogastric animals are bacteria from the Bacillus, Bifidobacterium and Lactobacillus genera and yeasts from Saccharomyces cerevisiae genus. The use of S. cerevisiae and Aspergillus oryzae is popular among adult ruminants, leading to weight gain both in calves and bullocks. In pre-ruminant cattle, the use of lactic bacteria (Lactobacillus and Bifidobacterium) also deserves some interest. In the field of chemical probiosis, the use of fructo- and gluco-oligosaccharides, capable of selectively stimulating the lactic bacteria, has yielded very interesting results both in monogastrics and in calves. Equally promising is the dietary supplementation with oligomannans and lectins. Such compounds saturate and bind to the enterocyte receptors which are present on the cell walls of pathogenic bacteria, thus preventing them from colonizing the intestinal lumen.