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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Ensiling is a method of preserving a moist crop. A moist crop can support the growth of a wide range of microorganisms, most of which will degrade the nutrient value to livestock. However, ensiling generally controls microbial activity by a combination of an anaerobic environment and a natural fermentation of sugars by lactic acid bacteria on the crop. This fermentation and the resulting low pH primarily suppress the growth of other anaerobic microorganisms. The fermentation can also inhibit yeasts, molds and aerobic bacteria, but the anaerobic environment is essential to preventing most of the spoilage microorganisms from growing. Inoculants have become the dominant additives for making silage. Homofermentative strains help guarantee a rapid suppression of anaerobic stains early in storage, increase dry matter recovery and have improved animal performance by means that we do not fully understand. Inoculants containing Lactobacillus buchneri, a heterofermentative species capable of fermenting lactic acid to acetic, are recent additives. The added acetic acid inhibits yeast and mold growth, increasing aerobic stability of silages at feeding.

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.

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Inoculants are used as silage additives to improve preservation efficiency and to enhance animal performance. In most commercially available inoculants, homofermentative lactic acid bacteria (LAB) have been used because they are fast and efficient producers of lactic acid, improving natural silage fermentation. Specific LAB inuculants may also have beneficial effects on animal performance even if there is no effect on fermentation. However, these types of inoculants are not always advantageous. They do not necessarily prevent sermentation by clostridia in moist silages, and they sometimes impair the aerobic stability of grass and small grain silages. Therefore, new criteria for silage inoculants should be established which consider the specific needs of the crop being ensiled. New approaches which are being taken to develop improved inoculants for silage include the following: (1) using LAB isolates which are more specific to the target crops; (2) inclusion of heterofermentative LAB to produce volatile fatty acids to inhibit yeasts and moulds upon aerobic exposure; (3) inclusion of organisms other than LAB in inoculants to inhibit detrimental microorganisms; (4) selection or engineering of LAB strains to inhibit specific microorganisms; and (5) cloning and expression of genes which would enable selected LAB strains to utilize polysaccharides in crops which are low in soluble carbohydrates. Many of these new strategies for formulating inoculants are being tested, but further research is needed to determine the most successful approaches.

Extensive protein hydrolysis after harvest and during fermentation is characteristic of forage legumes preserved as silage. Differences in proteolysis among species have been observed, but plant characteristics associated with these differences have not been well defined. This study was conducted to determine if tannins play a role in modifying N transformations associated with the preservation of forage legumes as silage. In 1987, 12 legume genotypes (representing six species) were field grown and analyzed for tannin concentrations pre‐ and post‐ensiling dry matter (DM), pH, and N forms. In 1988, 18 genotypes (representing seven species) were evaluated in a similar manner. Tannin concentrations range from 0 to 27 g tannic acid equivalents kg−1 DM in 1987 and 0 to 31 g in 1988. Dry matter concentration pH, and concentration of total N, soluble nonprotein N (SNPN), free amino acid N, and ammonia N of fresh and ensiled herbage were within the range of previous literature reports for forage legumes. The proportion of total N in the form of SNPN after 35 d ensiling ranged from 32 to 73% in 1987 and 26 to 69% in 1988 and was negatively related to tannin concentration (r2 = 0.75). Within sericea lespedeza [Lespedeza cuneata (Dum‐Cours) G. Don], the only species with substantial variation for both tannin and silage SNPN concentrations r2 values were 0.81 in 1987 and 0.88 in 1988. Red clover(Trifolium pratense L.) and cicer milkvetch( Astragalus cicer L.) did not contain measurable levels of tannins, but exhibited lower proteolysis than alfalfa (Medicago sativa L.). These results suggest that tannins play a major role in limiting proteolysis some legumes during ensiling, but other factors also are involved.

Recent advances in silage microbiology are reviewed. Most new techniques in silage microbiology use the polymerase chain reaction (PCR) to make copies of a portion of the DNA in microorganisms. These techniques allow us to identify and quantify species as well as do community analysis. The PCR-based techniques are uncovering new species, both bacteria and fungi, during storage and feeding. Silage inoculants are widely available, but of greater interest has been research investigating why inoculants are so successful. Various inoculant strains have been found to produce bacteriocins and other compounds that inhibit other bacteria and fungi, improving their chances for success. In vitro ruminal fermentation research is showing that some inoculated silages affect rumen microorganisms, reducing methane in some cases and increasing microbial biomass production in others. Better understanding of silage microbiology will allow us to better manage silos and develop better inoculants to improve silage quality.