The present invention relates to isolated polypeptides and isolated nucleic acid sequences encoding the polypeptides, as well as methods for producing and using the polypeptides in animal feed. An example of a polypeptide of the invention is the so-called L12 protein from Bacillus licheniformis ATCC 14580 which improves the Feed Conversion Ratio (FCR) and/or acts as a gut microflora modulator. The invention furthermore relates to the probiotic use of strains of Bacillus which produce proteins related to L12.