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Aims:  Grass silage is the product formed by a natural lactic acid bacterial fermentation when grass is stored under anaerobic conditions, and represents an important ruminant feedstuff on farms during winter. Of the two commonly employed methods of ensiling forage, baled silage composition frequently differs from that of comparable precision‐chop silage reflecting a different ensiling environment. The aim of this study was to investigate the dynamics of the silage fermentation in wilted grass and between ensiling systems. Methods and Results:  Fermentation dynamics were examined using traditional methods of silage analyses, including microbial enumeration and analysis of fermentation products, and culture‐independent terminal restriction fragment length polymorphism (T‐RFLP). A successful fermentation was achieved in both systems, with the fermentation (increase in lactic acid bacteria and lactic acid concentration, decrease in pH) proceeding rapidly once the herbage was ensiled. Conclusions:  Under controlled conditions, little difference in silage quality and microbial composition were observed between ensiling systems and this was further reflected in the T‐RFLP community analysis. Significance and Impact of the Study:  T‐RFLP proved a potentially useful tool to study the ensilage process and could provide valid support to traditional methods, or a viable alternative to these methods, for investigating the dynamics of the bacterial community over the course of the fermentation.

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The chemical composition of baled silage frequently differs from that of comparable conventional silage. The extents of wilting, chopping, compaction and air infiltration potentially contribute to these differences in conservation characteristics. An experiment was organized in a 3 (0, 24 or 48-h wilting to influence herbage dry-matter content) · 2 (unchopped or chopped) · 2 (with or without compaction) · 2 (with or without air infiltration) factorial arrangement of treatments, to elucidate the relative effects of these factors on the conservation characteristics of ensiled grass. Dry-matter content of herbage and infiltration of air had a greater effect on silage conservation characteristics than chopping and compaction. The main interactions were between wilting and air infiltration, wilting and compaction, and compaction and air infiltration. Air infiltration stimulated a secondary fermentation in the unwilted herbage, reflected in a large increase (P < 0AE001) in clostridial activity. As wilting progressed, air infiltration facilitated yeast respiration of watersoluble carbohydrates (WSC) and resulted in an increase (P < 0AE001) in in-silo fresh-weight losses. Compaction reduced (P < 0AE05) silage pore space and, as a result, the extent to which air could penetrate the silage mass. Compaction of the wilted herbage restricted respiration and was reflected in increased (P < 0AE05) concentrations of WSC and in a reduction (P < 0AE001) in fresh-weight loss. The rapid achievement and maintenance of adequately anaerobic conditions is the primary requirement for baled silage. This study showed that failure to achieve this will lead to progressively greater losses, especially with drier herbage.

Aims:  Grass silage is an important ruminant feedstuff on farms during winter. The ensilage of grass involves a natural lactic acid bacterial fermentation under anaerobic conditions, and numerous factors can influence the outcome of preservation. The aim of this study was to investigate the effect of dry matter concentration, ensiling system, compaction and air infiltration on silage bacterial community composition. Methods and Results:  The impact of these factors was examined using conventional methods of microbial analysis and culture‐independent Terminal Restriction Fragment Length Polymorphism (T‐RFLP). Silage fermentation was restricted in herbage with a high dry matter concentration, and this was reflected in a shift in the bacterial population present. In contrast, ensiling system had little effect on bacterial community composition. Air infiltration, in the absence of compaction, altered silage bacterial community composition and silage pH. Conclusions:  Dry matter concentration and the absence of compaction were the main factors affecting silage microbial community composition, and this was reflected in both the conventional culture‐based and T‐RFLP data. Significance and Impact of the Study:  T‐RFLP proved a useful tool to study the factors affecting ensilage. Apart from monitoring the presence or absence of members of the population, shifts in the relative presence of members could be monitored.

The composition of baled silage frequently differs from that of comparable conventional silage. A factorial experiment was conducted with three wilting treatments (0, 24 or 48 h) · three ensiling systems [unchopped grass in bales, unchopped grass in laboratory silos (LS), precision-chopped grass in LS] · six stages of ensiling to (i) confirm that the fermentation of unchopped grass in LS could be used as an adequate model for baled silage fermentation, (ii) quantify the differences between baled silage and silage made from precision-chopped herbage across a range of dry-matter contents and (c) quantify the fermentation dynamics within the various treatments. The onset of fermentation as evidenced by the accumulation of fermentation products and the decline in pH were slower (P < 0AE05) in baled silage compared with silage made from precision-chopped herbage. Furthermore the pH (P < 0AE001) and overall concentration of fermentation acids (P < 0AE01) were lower while ammonia-N concentration was generally higher in baled silage, making it more conducive to the activities of Clostridia, Enterobacteria and yeast. Numbers of Enterobacteria were higher (P < 0AE001) in baled silage in the early stages of ensilage and persisted in baled silage at the end of the storage period. The implications of a slower onset of fermentation in baled herbage are greater in farm practice, as the fermentation would be further restricted by a more extensive wilting of the herbage prior to ensiling.