Because we want high-producing and healthy animals, special attention should be paid to the hygienic quality of the silage. Silages either contain or are contaminated with hazardous substances. There are several options for preventing and protecting silage from spoilage. Chemical and microbiological risks are mainly associated with insufficiently fermented silages. They can be avoided by using correct silage production practices and by creating conditions that promote a rapid and sufficient reduction in silage pH, e.g. by applying suitable silage preparations. It is also important to prevent aerobic spoilage after opening the silo.