Silage review: Animal and human health risks from silage

Abstract

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 include Clostridium botulinum, Bacillus cereus, Listeria monocytogenes, Shiga toxin-producing Escherichia coli, Mycobacterium bovis, and various mold species. High concentrations of C. botulinum in silage have been associated with cattle botulism. A high initial concentration of C. botulinum spores in forage in combination with poor silage fermentation conditions can promote the growth of C. botulinum in silage. The elevated pH level that is generally associated with aerobic deterioration of silage is a major factor influencing concentrations of L. monocytogenes, Shiga toxin-producing E. coli, and molds in silage and may also encourage survival and growth of M. bovis, the bacterium that causes bovine tuberculosis. Soil is a major source of B. cereus spores 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.

Silage fermentation—updates focusing on the performance of micro‐organisms

“…; Driehuis et al . ). The spore cycle in milk production systems has been discussed by Pahlow et al .…”

“…The STEC O157:H7 can be found in silage, with cattle considered the main reservoir of this strain (Driehuis et al . ; Queiroz et al . ).…”

“…One example is a strain of Escherichia coli O157:H7 Shiga toxin-producing (STEC), an important pathogen to humans. The STEC O157:H7 can be found in silage, with cattle considered the main reservoir of this strain (Driehuis et al 2018;Queiroz et al 2018). However, STEC O157:H7 has not been shown to be pathogenic to cattle in natural infections.…”

Ensiling in 2050: Some challenges and opportunities

“…Potential hazards to human, animal and food safety from silage have been reviewed by Driehuis (2013) and Driehuis, Wilkinson, Jiang, Ogunade, and Adesogan (2018). Undesirable microorganisms and their toxins can be present in silage when it is consumed by the animal due to contamination of the crop pre-harvest, during storage and during feed-out.…”

In Preparation for Outdoor Pharming: Griffithsin Can Be Expressed in Nicotiana excelsiana and Retains Activity After Storage as Silage

“…Silage is typically stored in a silo, which is a typically oxygen limiting container that does not allow oxygen to come into contact with the plant material. This allows the silage to undergo anaerobic fermentation and produces acid to create a hostile environment for micro-organisms that may cause spoilage (Driehuis et al, 2018). While ensiled plant material is common for livestock, ensiling plant material for plant-based pharmaceuticals (pharming) was proposed by Hahn et al (2014).…”