Mycotoxins in silage

Purpose of review: This paper reviews the present knowledge on mycotoxins in silage, focusing on grass and maize silage. This includes the occurrence of filamentous fungi preand postharvest, possible and confirmed mycotoxins in silage, toxicological concerns and means to prevent the problem. Findings: Preharvest contamination of grass and maize by Fusarium, Aspergillus and Alternaria can lead to contamination of silage. Well known mycotoxins deoxynivalenol (DON), zearalenone (ZEA), fumonisins and aflatoxins have been detected in silages but concentrations seldom exceed regulatory limits. It also appears that DON, ZEA and fumonisins are degraded in silage, but exact mechanisms are unknown. Postharvest spoilage is dominated by Penicillium roqueforti, Aspergillus fumigatus and Zygomycetes. Both P. roqueforti and Asp. fumigatus produce a wide range of secondary metabolites, some of them confirmed mycotoxins, others with antimicrobial or immunosuppressive effects. Some fungal metabolites have been detected in silage but many have not been looked for. Evidence for acute toxicosis caused by contaminated silage is rare. Mycotoxins in silage are more often associated with less specific symptoms like ill-thrift or decreasing yield. This may be caused by long-term exposure to the complex mixture of secondary metabolites that silage can contain. Mycotoxins with antimicrobial effects may also affect ruminant digestion. To prevent postharvest spoilage of silage the most important factor is omission of oxygen. Additives can improve certain silage properties but they are not conclusively an advantage and cannot replace good silage management. Directions for future research: The effects of long-term exposure and of complex mixtures of bioactive fungal compounds are subjects of interest. Especially high-yielding livestock may be subject to sub-acute symptoms under these conditions. There is also a need for analytical methods with specificity and accuracy to determine many of the less known mycotoxins and secondary metabolites in silage as well as possible unknown compounds.