Silage review: Animal and human health risks from silage

摘要

Silage may contain several agents that are potentially hazardous to animal health, the safety of milk or other animal food products, or both. This paper reviews published literature about microbial hazards, plant toxins, and chemical hazards. Microbial hazards includeClostridium botulinum,Bacillus cereus,Listeria monocytogenes, Shiga toxin-producingEscherichia coli,Mycobacterium bovis, and various mold species. High concentrations ofC. botulinumin silage have been associated with cattle botulism. A high initial concentration ofC. botulinumspores in forage in combination with poor silage fermentation conditions can promote the growth ofC. botulinumin silage. The elevated pH level that is generally associated with aerobic deterioration of silage is a major factor influencing concentrations ofL. monocytogenes, Shiga toxin-producingE. coli, and molds in silage and may also encourage survival and growth ofM. bovis, the bacterium that causes bovine tuberculosis. Soil is a major source ofB. cereusspores in silage; growth of this bacterium in silage appears to be limited. Hazards from plant toxins include pyrrolizidine, tropane and tropolone alkaloids, phytoestrogens, prussic acid, and mimosine, compounds that exist naturally in certain plant species that may contaminate forages at harvesting. Another group of toxins belonging to this category are ergot alkaloids, which are produced by endophytic fungal species in forages such as tall fescue grass, sorghum, and ryegrass. Varying effects of ensiling on the degradation of these plant toxins have been reported. Chemical hazards include nitrate, nitrite, and toxic oxide gases of nitrogen produced from nitrate and high levels of butyric acid, biogenic amines, and ammonia. Chemical and microbiological hazards are associated with poorly fermented silages, which can be avoided by using proper silage-making practices and creating conditions that promote a rapid and sufficient reduction of the silage pH and prevent aerobic deterioration.