Additives have been available for enhancing silage preservation for decades. This review covers research studies published since 2000 that have investigated the efficacy of silage additives. The review has been divided into 6 categories of additives: homofermentative lactic acid bacteria (LAB), obligate heterofermentative LAB, combination inoculants containing obligate heterofermentative LAB plus homofermentative LAB, other inoculants, chemicals, and enzymes. The homofermentative LAB rapidly decrease pH and increase lactic acid relative to other fermentation products, although a meta-analysis indicated no reduction in pH in corn, sorghum, and sugarcane silages relative to untreated silages. These additives resulted in higher milk production according to the meta-analysis by mechanisms that are still unclear. Lactobacillus buchneri is the dominant species used in obligate heterofermentative LAB silage additives. It slowly converts lactic acid to acetic acid and 1,2-propanediol during silo storage, improving aerobic stability while having no effect on animal productivity. Current research is focused on finding other species in the Lb. buchneri group capable of producing more rapid improvements in aerobic stability. Combination inoculants aim to provide the aerobic stability benefits of Lb. buchneri with the silage fermentation efficiency and animal productivity benefits of homofermentative LAB. Research indicates that these products are improving aerobic stability, but feeding studies are not yet sufficient to make conclusions about effects on animal performance. Novel non-LAB species have been studied as potential silage inoculants. Streptococcus bovis is a potential starter species within a homofermentative LAB inoculant. Propionibacterium and Bacillus species offer improved aerobic stability in some cases. Some yeast research has focused on inhibiting molds and other detrimental silage microorganisms, whereas other yeast research suggests that it may be possible to apply a direct-fed microbial strain at ensiling, have it survive ensiling, and multiply during feed out. Chemical additives traditionally have fallen in 2 groups. Formic acid causes direct acidification, suppressing clostridia and other undesired bacteria and improving protein preservation during ensiling. On the other hand, sorbic, benzoic, propionic, and acetic acids improve silage aerobic stability at feed out through direct inhibition of yeasts and molds. Current research has focused on various combinations of these chemicals to improve both aerobic stability and animal productivity. Enzyme additives have been added to forage primarily to breakdown plant cell walls at ensiling to improve silage fermentation by providing sugars for the LAB and to enhance the nutritive value of silage by increasing the digestibility of cell walls. Cellulase or hemicellulase mixtures have been more successful at the former than the latter. A new approach focused on Lb. buchneri producing ferulic acid esterase has also had mixed success in improving the efficiency of ...

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An overview was made of dry matter (DM) and quality losses that occur during the ensiling process from the field through the feeding phase. The aim was to review the relevant published literature of the last 15 yr focusing on developments achieved after the publication of the book Silage Science and Technology. This review discusses the factors affecting DM and quality losses in terms of field and pre-ensiling conditions, respiration and temperature at ensiling, fermentation patterns, methods of covering and weighting the silage cover, and management of aerobic deterioration. The possibility of reducing DM and quality losses during the ensiling process requires knowledge of how to measure losses on farm and establish the status of the silage during the feed-out phase, implementing the most effective management practices to avoid air exposure during conservation and reduce silage aerobic deterioration during feeding. The paper concludes with future perspectives and recommended management practices to reduce losses and increase efficiency over the whole ensiling process in view of increasing sustainability of the livestock production chain.