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Abstract: Highlights of progress in the production of silage over the past 50 years include the introduction of improved hybrids of maize (Zea mays L.), the forage harvester, the big baler, polyethylene covering for horizontal silos, stretch‐wrap film for bales and novel additives designed to improve the fermentation and aerobic stability of silage. The key biochemical pathways in the silage fermentation have been described together with the effects of microbial and chemical additives on fermentation and aerobic stability during the feed‐out phase. The significance of oxygen and water in silage fermentation has been quantified and efficacy of covering silos has been established, with recent progress in the development of oxygen barrier film. Future perspectives include improving food safety and animal health by increasing the hygienic quality of silage, reducing the environmental impact of silage by decreasing loss of nitrogen to soil and atmosphere, reducing methanogenesis in the rumen and increasing methane yield from silage as biofuel, and the use of silages as feedstocks for multiple end uses in biorefineries. [ABSTRACT FROM AUTHOR]

Silage making involves preserving forage crops by fermentation of water-soluble carbohydrates (sugars) to organic acids. The fermentation is relatively uncontrolled and inadequate acidification can allow the growth of undesirable microorganisms such as enterobacteria and clostridia. Ingress of oxygen to the outer layer of the silo or bale during the storage period encourages growth of yeasts and moulds. Mycobacterium bovis may survive in silages with pH above 5.0. Outgrowth of clostridia in aerobically deteriorating silage can lead to high counts of butyric acid spores in silage that can contaminate milk and cheese. Milk may be contaminated with Penicillium toxins and be rejected for containing antibiotics. Specific disease risks to livestock from poorly preserved silage include bacterial endotoxicosis, listeriosis, botulism, mycotoxicosis and nitric acid poisoning in addition to reduced feed value. Rapid acidification is essential once the crop is ensiled to restrict the growth of enterobacteria, listeria and clostridia. Oxygen barrier film, in addition to reducing loss of dry matter during the storage period, prevents clostridial outgrowth in the outer layer of the silo and is also likely to reduce the risk of listeriosis. [ABSTRACT FROM AUTHOR]

Losses of organic matter in the outer layers of bunker silos covered with conventional polyethylene ( PE) plastic can be substantial due to oxygen transmission through the plastic top-covering film during the post-ensiling storage period. The effect of two silo covering materials, oxygen barrier ( OB) film (45 μm thickness) and clear PE film (50 μm thickness), as underlays to a white-on-black PE plastic top cover (120 μm thickness), was assessed in the outer layer of whole-plant maize silage stored in three large bunker silos in the People's Republic of China. Samples of the crop at harvest and of silage from the upper 45 cm layer at 5 months post-ensiling, prior to removal of silage for feed-out, were analysed for DM, fermentation profile and chemical composition. Loss of OM was estimated from concentrations of ash in the crop at harvest and in the silage. Differences between underlay films in silage fermentation profile were small. Silage protected with OB underlay film had higher mean concentration of starch ( p < .008) and higher mean NDF digestibility ( p < .003) than silage under PE underlay film. Concentrations of ash were lower ( p < .001) for silage covered with OB film than for PE film in all three trials. Mean estimated losses of OM were 170 g/kg for OB underlay film and 232 g/kg for PE underlay film ( p < .001), and whole-silo estimated net economic benefits to OB underlay film ranged from 0.17 to 0.74 US $ per tonne fresh crop ensiled. [ABSTRACT FROM AUTHOR]