Factors influencing aerobic deterioration of silages and changes in chemical composition after opening silos

In five separate experiments, silages made from Italian ryegrass by eight treatments were transferred into expanded polystyrene containers and the occurrence of deterioration was observed at 25–30 °C and 10–15 °C or 5–10 °C by measuring changes in temperature during 7 days. The treatments were: heavily wilted, slightly wilted, unwilted, and 2% glucose added to unwilted grass—all carried out with and without addition of 0.5% sodium propionate (in one experiment a mixture of 0.08% sodium nitrite and 0.04% hexamethylenetetramine was used instead). Silages tended to be less stable at 25–30 °C than at 10–15 °C ambient temperature, although some were stable even at the higher temperature. At 5–10 °C, no deterioration occurred. No definite relationship was found between occurrence of deterioration and the contents of dry matter or WSC in silage or density in the container. Although deterioration took place more often at pH lower than 4.0, no relationship between pH and deterioration was recognised in the range 4.0–7.0. Silages tended to be more stable when contents of total or lactic acid in fresh matter were high. Silages with no added propionic acid were more susceptible to deterioration but some were unstable even at high propionic acid levels. No aerobic deterioration took place with silages containing more than 0.5% butyric acid. With the deteriorated silages, rises in pH value (except for those with originally high pH), marked decreases in lactic acid and/or WSC were observed. Propionic acid content tended to remain constant in the stable silages but there were a few exceptions. Losses of WSC plus organic acids during deterioration were found to be higher with the silages of high WSC contents. Although changes with the stable silages were generally small, a few of them showed some decrease in WSC and/or organic acids.     

Conservation of fresh and wilted grass in air-tight metal containers

Fresh and wilted timothy-meadow fescue herbage of 19 and 46.6° dry matter content, respectively, was ensiled in rubber-sealed steel cylinders 5 ft deep and 3 ft in diameter. Mean dry matter losses from all silos were about 6%. All silages were well preserved, the wilted material containing less lactic acid and volatile acids and having a higher pH. The dry matter digestibility coefficients from fresh and wilted grass silages were 71.5 and 70.2%, respectively, and were slightly higher than for the grass before ensilage. Ensilage resulted in a fall in metabolisable energy of the wilted grass. Intake of wilted silage by sheep was higher than that of silage from fresh grass.     

Chemical changes and losses during the ensilage of wilted grass treated with formic acid

Formic acid (85%) was added to wilted perennial ryegrass (36% dry matter) at the rate of 0.39%. Changes during ensilage of this material were compared with changes occurring during ensilage of untreated wilted ryegrass and freshly harvested herbage. All silages were well preserved, of low volatile N content and contained only traces of butyric acid. Formic acid restricted fermentation in the wilted grass resulting in silage of high water-soluble carbohydrate content (15.3%) compared with untreated wilted (4.7%) and fresh (1.2%) silages. Results of microbiological studies indicated that yeasts were more active in the formic acid-treated herbages. Surface waste production and fermentation plus oxidation losses were higher in the acid-treated wilted silages (21%) than in the untreated wilted materials (14%).     

Chemical changes and losses during the ensilage of wilted grass

Two experiments were carried out; in the first, wilted Italian ryegrass at two different dry matter (DM) levels (34% and 47%) was ensiled; in the second, fresh grass (15.9% DM) and similar herbage wilted to 30.3% DM were ensiled. Total edible DM losses from the wilted silages were low and ranged from 6.7 to 10.4%. Changes in individual sugars and organic acids were followed. The residual amounts of sugars in the wilted silages were directly related to the degree of wilting. All silages were well preserved, but little fermentation had occurred in the material wilted to 47 % DM. From a knowledge of the sugars lost and amounts of mannitol and ethanol formed it has been possible to examine quantitatively the main chemical changes during the ensilage of the wilted materials. The results confirm the efficiency with which wilted grass is anaerobically conserved.     

Conservation of wilted and unwilted grass ensiled in air-tight metal containers with and without the addition of molasses

Italian ryegrass was ensiled in gas-tight silos in unwilted (21% dry matter) and wilted (42% dry matter) conditions without an additive and with the addition of molasses at a mean level of 8% in the dry matter. The total dry matter losses were 8·7, 7·2, 4·5 and 5·0% for unwilted, molassed unwilted, wilted, and molassed wilted grass silages respectively. The silages were all well preserved but the extent of fermentation had been reduced in the wilted silages. The losses of individual sugars during the silage process and the products of fermentation were used to assess the pathways of fermentation. The dominant pathway of fructose utilisation was by heterolactic fermentation. The addition of molasses reduced the ratio of fructose: glucose in the ensiled material and reduced the amount of mannitol produced during the ensilage process.     

The occurrence and prevention of ethanol fermentation in high‐dry‐matter grass silage

Ethanol is a common, usually minor fermentation product in ensiled forages, the major product being lactic acid. Occasionally, high levels of ethanol are found in silages. The aim of this study was to determine the incidence of high‐dry‐matter (DM) grass silages containing ethanol as the main fermentation product (ethanol silages), to describe the fermentation process in such silages and to determine the effect of grass maceration prior to wilting and addition of a bacterial inoculant containing Lactobacillus plantarum and Enterococcus faecium strains on fermentation. Twenty‐one laboratory silages produced between 1993 and 1995, 21 farm silages produced between 1980 and 1989 and 36 farm silages produced in 1995 (all produced without additive) were examined for pH and chemical composition. Dry matter (DM) loss during ensilage was determined for the laboratory silages only. Four laboratory silages were identified as ethanol silages. Mean concentrations of ethanol, lactic acid and acetic acid were 48.1, 15.5 and 6.0 g kg⁻¹ DM respectively. In the silages that contained lactic acid as the main fermentation product (lactic acid silages) these values were 7.7, 45.5 and 15.1 g kg⁻¹ DM. Mean DM loss and pH were 62.8 g kg⁻¹ DM and 5.32 respectively for ethanol silages and 24.4 g kg⁻¹ DM and 4.69 for lactic acid silages. There was no difference between ethanol silages and lactic acid silages in the mean concentration of ammonia‐N (94 g kg⁻¹ total N), and butyric acid was not detected (<0.2 g kg⁻¹ DM), indicating that both types of silages were well preserved. Analysis of the composition of the grass at ensiling showed a positive correlation between the concentration of soluble carbohydrates and the development into ethanol silage. Analysis of the farm silages indicated that 29% of the silages produced between 1980 and 1989 and 14% of those produced in 1995 were ethanol silages. Maceration prior to wilting and addition of silage inoculant improved lactic acid fermentation and prevented high ethanol levels. The micro‐organisms responsible for ethanol fermentation as well as the implications of feeding ethanol silages to livestock remain to be resolved. © 2000 Society of Chemical Industry     

Ensiling characteristics and aerobic stability of direct‐cut and wilted grass silages inoculated with Lactobacillus casei or Lactobacillus buchneri

Two experiments were conducted to study the effects of wilting and inoculating Lactobacillus casei or Lactobacillus buchneri on the fermentation and aerobic stability of grass silages. Chopped Italian ryegrass (IR) and Festulolium (FE) were ensiled with or without wilting and added L casei (>10⁶ cfu g^?1 fresh matter (FM)) or L buchneri (>10⁶ cfu g^?1 FM). Silos were opened after 120 days and microbial counts, fermentation products and aerobic stability were determined. Addition of L casei increased lactic acid and decreased acetic acid and dry matter loss regardless of wilting and forage species. Inoculation of L buchneri decreased lactic acid and increased acetic acid and 1,2‐propanediol, while the effects appeared greater in direct‐cut than in wilted grass silages. Although 1,2‐propanediol accumulated in FE silage, the diol was degraded further to propionic acid and 1‐propanol in IR silage. The activity of 1,2‐propanediol degradation was lowered when IR was wilted prior to ensiling; 1,2‐propanediol remained and the production of propionic acid and 1‐propanol was less than one‐third of that in direct‐cut silage. Regardless of forage species, addition of L buchneri increased dry matter loss compared with the untreated control, whereas the loss was not significant in wilted silages. Ammonia production was increased by L buchneri in direct‐cut but not in wilted silages. No heating was observed with or without inoculation in direct‐cut IR silage after exposure to air. Other silages were deteriorated when L buchneri was not inoculated, while the spoilage was accelerated when L casei was added to FE. Copyright © 2005 Society of Chemical Industry     

Feeding value of silage: Silages made from freshly cut grass,wilted grass and formic acid treated wilted grass

Formic acid (850 g/kg) was added to wilted perennial ryegrass (dry matter = 360 g/kg) at the rate of 3.9 g/kg before ensiling. The feeding value of the resulting silage was compared with those of silages made from the wilted grass and the freshly cut grass, and with the grass itself in metabolism trials with sheep. Intakes of dry matter were depressed by fermentation, being 12.3, 9.7 and 8.5 g/kg liveweight for the acid treated, prewilted and directly ensiled material respectively. Fermentation improved the metabolisable energies which were 11.6, 12.0, 11.4 and 13.6 MJ/kg DM for the grass, and the acid treated, wilted and directly ensiled materials. In general, fermentation reduced the intake of metabolisable energy and the production potential of the material. The major factor affecting the feeding value of silage is its acceptability to the animal in terms of dry matter intake. High dry matter intakes are best achieved by limiting fermentation.     

Conservation of wilted herbage ensiled in sealed plastic containers,with and without the addition of urea,and its intake by sheep

Timothy-meadow fescue grass was wilted to 27.7–33.9% dry matter content and two silos were filled with the wilted material alone and two with the wilted herbage to which urea, at a level of 1.38% of the dry matter ensiled, was added. The mean dry matter loss from the control silages was 16.7% and from the urea-treated silages 11.4%. No urea could be detected in the silage made from the urea-treated herbage. There was no evidence for any major differences in the fermentation pathways between the control and urea-treated silage. Voluntary intake of control and urea-treated silage by sheep was similar (1.7 times the maintenance metabolisable energy requirement) so that nitrogen intake was higher when the urea-silage was fed. No toxic effects of the treated silage were observed when assessed by blood urea and ammonia levels.     

Ensiling characteristics and ruminal degradation of Italian ryegrass and lucerne silages treated with cell wall-degrading enzymes

Two experiments were carried out to investigate the effect of added cell wall-degrading enzymes at ensiling on the fermentation and in situ degradation of grass and legume silages. Primary growths of Italian ryegrass (Lolium multiflorum Lam) and lucerne (Medicago sativa L) were wilted and ensiled in laboratory-scale silos with or without enzymes. Silages were opened at 2, 5, 15 and 45 days after storage; the fermentation quality and the contents of cell wall components (NDF, ADF, ADL) were determined. The 45 day silages were subjected to in situ incubation experiments, and the kinetics of DM and NDF degradation was estimated. The enzyme treatment enhanced the lactic acid production (P < 0.01) and reduced the pH value (P < 0.01) of both Italian ryegrass and lucerne silages. The contents of cell wall components, however, were not affected by enzymes, except for NDF of Italian ryegrass silage. The in situ incubation experiments revealed that added enzymes increased the rapidly degradable DM (P < 0.01) and appeared to decrease the rate of degradation of DM and NDF of Italian ryegrass silage. The rapidly degradable DM was not altered when lucerne was treated, but the rate of degradation of NDF was significantly reduced (P < 0.05). These results suggest that although added cell wall-degrading enzymes could improve the preservation of grass and legume silages, the effects on ruminal degradation may be different according to the herbage treated. Enzymatic hydrolysis during ensilage may be restricted to easily digestible cell walls, leaving relatively less digestible components that would be retained in treated silages. © 1999 Society of Chemical Industry     

The use of caproic acid to prevent aerobic deterioration of silages after opening,with special reference to the amounts and time of application

The effectiveness of caproic acid (hexanoic acid) addition to silages prepared from Italian ryegrass or cocksfoot (dry matter 16.3–34.5%) in preventing aerobic deterioration after opening was investigated in five experiments with varying amounts and times of application. Silages prepared in PVC bag silos were transferred to expanded polystyrene containers and left in a room at 25°C for 7 days with access to air. Aerobic deterioration was judged by rise in temperature, increase in pH and changes in the counts of yeasts and moulds. A low dry matter silage containing a fairly large amount of butyric acid was stable, and another low dry matter silage was relatively stable. Silages made from wilted grass deteriorated. Application of 50 mmol/kg grass at ensiling prevented deterioration in all cases. The effect was also observed with 50 mmol addition at opening, 10 mmol at ensiling and 10 mmol at opening in that order.     

Relationship between oven and toluene dry matter in grass silage

Dry matter (DM) contents of 205 silages were determined by toluene distillation and oven drying at 100°C. The toluene distillation method gave values up to 11% higher than the oven drying method, the largest differences occurring with silages of high volatile fatty acid concentration, low lactic acid concentration and high ammonia nitrogen content expressed as a percentage of total nitrogen. Highly significant (P < 0.01) correlations were shown between toluene dry matter and oven dry matter for various ranges of ammonia nitrogen, and equations are presented which allow toluene dry matter to be readily estimated on a routine basis for grass silage.     

Prediction models of silage fermentation products on crop composition under strict anaerobic conditions: A meta-analysis

A meta-analysis was conducted to establish linkages between crop and fermentation variables. Data from well-controlled mini silage studies were used in which no additives had been used and no ingress of air had occurred. The silage set consisted of data on crop chemical composition and epiphytic lactic acid bacteria count, and fermentation products (organic acids, alcohols, and ammonia-N) from 118 silages made from 30 grass, 7 legume, 15 grass and legume mixtures, and 66 whole-crop maize samples. The prediction models for fermentation products on crop variables were obtained by stepwise multiple regression analysis. Perennial forage and maize silages were analyzed separately. The best models were obtained for acetic acid in perennial forage silages, with a coefficient of determination of 0.63, and for lactic acid and ethanol in whole-crop maize silages, with coefficients of determination of 0.84 and 0.61, respectively. Fermentation products of perennial forage and maize silages were best related to dry matter and crude protein contents, respectively. Overall, the prediction equations were weak.     

Effect of arachis oil on the conservation of heavily wilted herbage ensiled in plastic containers. I. Effect on silage fermentation quality, nutritive value, nutrient losses and intake by sheep

Arachis oil was added to heavily wilted herbage of approximately 40% dry matter, before ensiling in polyethylene containers. The oil was added at a mean level of 4·16% of the total dry matter ensiled. The mean dry matter loss from the two control and the two oil-treated silages teas approximately 13%. There was a lower loss as inedible waste in the oil-treated silages and mould growth appeared to be inhibited by the oil. There was a lower percentage of butyric acid and propioiuc acid in the oil-treated silages than in the control silages, this effect being statistically significant. Ensiling resulted in a greater fall in digestibility of the control material than in the oil-treated material. The oil-treated silages had higher metabolisable energy contents than the control silages but the dry matter intakes of both silages by sheep were low.     

The effects of some additives on the microflora of silage

The microflora of experimental batches of grass silage treated with formaldehyde, with formaldehyde plus formic acid, or with sodium benzoate and held at a constant temperature of 20°C was examined during fermentation and after exposure to air. The formaldehyde treatments inhibited the development of lactobacilli during fermentation but their biocidal effect did not persist and on exposure to air microbial numbers increased and the pH of the silages rose at a similar rate to that in untreated silage. Treatment with sodium benzoate had little effect on fermentation but its biostatic, particularly fungistatic, activity persisted through 17 days of exposure to air during which the pH did not rise and fungal numbers remained low. The yeast flora of all treatments was predominantly of fermenting species similar to that found in stack silages but the mould flora, of Geotrichum candidum, Mucor spp. and Penicillium spp., was dissimilar and could be related to the lack of heating in the experimental silages.     

Effects of a commercial inoculant of lactic acid bacteria on the composition of silages made from grasses of low dry matter content

The efficacy of a commercial inoculant, Natuferm, which contains multiple strains of lactic acid bacteria, was examined in seven experiments using 6 m³ pilot-scale silos. Samples taken during the fermentation period were analysed and compared with samples from untreated controls and formic acid silages. Good quality silages were obtained with crops of low dry matter content (12–14%) and with a water soluble carbohydrate content of 1·5% related to fresh weight. The addition of Natuferm resulted in increased lactic acid levels (50–90%) during the initial fermentation, and pH dropped faster compared with the untreated controls. Compared with the formic acid silages the level of enterobacteria declined rapidly in both the inoculated and untreated silages. In two of the experiments a pronounced difference in enterobacterial count was observed between the Natuferm and control silages on day 2. The effluent volumes were recorded, and the pH and the dry matter content of the effluent were determined. Compared with the formic acid silages, a 40% average reduction of the effluent flow was observed from Natuferm silages, and in most experiments there was also a reduced effluent volume compared with the controls. Analyses of 174 Natuferm silages and 73 formic acid silages from full scale (farm) silos revealed no significant differences in silage quality between the two additives. Natuferm silages with a dry matter content below 20% were not significantly different from silages with a dry matter content above 20%.     

Temperature during conservation in laboratory silos affects fermentation profile and aerobic stability of corn silage treated with Lactobacillus buchneri,Lactobacillus hilgardii,and their combination

The environment temperature and its effect on the temperature of silage is very important for the fermentation and subsequent quality of a silage. Obligate heterofermentative lactic acid bacteria (LAB) inocula, because of their ability to inhibit yeasts, have been developed to prevent the aerobic deterioration of silages. The temperature during silage conservation may also play an important role in the fermentation profile of silages. This study has evaluated the effect of temperature, during the conservation of whole crop corn silage, untreated or treated with different LAB inocula, on the fermentation profile and on the aerobic stability of the silage. Corn was harvested at 42% dry matter and either not treated (control) or treated with Lactobacillus buchneri NCIMB 40788 (LB) at 300,000 cfu/g fresh matter (FM); Lactobacillus hilgardii CNCM I-4785 at 150,000 cfu/g FM (LH₁₅₀); L. hilgardii CNCM I-4785 at 300,000 cfu/g FM (LH₃₀₀); or LB+LH at 150,000 cfu/g FM each. In an attempt to experimentally simulate temperature fluctuations in the mass or at the periphery of a silage bunker, corn was conserved in laboratory silos at a constant temperature (20 ± 1°C; MASS) or at lower and variable outdoor temperatures (PERIPH; ranging from 0.5 to 19°C), and the silos were opened after 15, 30, and 100 d of conservation. Lactic acid, acetic acid, and ethanol contents increased in all the silages over the conservation period. The lactic acid content was higher (+10%) in the silages kept at a constant temperature than those conserved at the lower and variable outdoor temperatures. The acetic acid was higher in the treated silages than in the control ones conserved at a constant temperature for 100 d. Moreover, 1,2-propanediol was only detected in the treated silages after at least 30 d at a constant temperature, whereas only traces were detected in the LB+LH treatment for the other temperature conditions. The yeast count decreased during conservation at a slower rate in PERIPH than in MASS and on average reached 2.96 and 4.71 log cfu/g for MASS and PERIPH, respectively, after 100 d of conservation. The highest aerobic stability values were observed for LH₃₀₀ (191 h) in the MASS silage after 100 d of conservation, whereas the highest aerobic stability was observed in LB+LH (150 h) in the PERIPH silages. After 7 d of air exposure, a pH higher than 4.5 and a higher yeast than 8.0 log cfu/g were detected in all the silages opened after 15 and 30 d of conservation. A pH value close to that of silo opening was detected in the LB, LH₁₅₀, and LH₃₀₀ silages conserved under MASS conditions after 100 d, whereas LB+LH was the most effective under PERIPH conditions. The temperature and its fluctuation during conservation of silage in laboratory silos influenced the fermentation, which in turn had an effect on the quality of silage and on the extent of the effect of LAB inocula.     

Cellulase and Bacterial Inoculant Effects on Cocksfoot and Lucerne Ensiled at High Dry Matter Levels

Limited information exists on the response of grass and legume silage to enzyme and bacterial inoculant treatments when wilted to drier than desired conditions. This study was undertaken to evaluate the impact of cellulase (from Trichoderma longibrachiatum) application rate, when combined with a bacterial inoculant (Lactobacillus plantarum and Pediococcus cerevisiae), on the fermentation characteristics of cocksfoot (Dactylis glomerata L) and lucerne (Medicago sativa L) ensiled at high dry-matter concentrations. Forages were wilted to near 600 g dry matter kg^-1 and cellulase, combined with inoculant, was applied at 0·30 ml kg^-1 herbage and at two, four and eight times this concentration (at least 2500 IU ml^-1). Cellulase was also applied alone at 0·60 ml kg^-1. Wilted forages were ensiled in laboratory silos for 60 days. Effect of cellulase application rate on neutral detergent fibre concentrations of the silages was small and inconsistent. Averaged across species, only the intermediate cellulase concentrations decreased neutral detergent fibre concentration (P=0·082). The limited cell-wall degradation was probably related to the high silage dry-matter and lignin concentrations. Cellulase combined with inoculant increased total fermentation, when averaged across species. In cocksfoot, cellulase combined with inoculant decreased pH and NH₃-N concentration but increased the lactic: acetic acid ratio of control silage, with most of the effect caused by the inoculant. Cellulase applied alone to lucerne caused a higher lactic: acetic acid ratio than the control or when combined with the inoculant at the same cellulase rate. Thus, the effect of cellulase–inoculant mixtures on silage quality varied among plant species, with cocksfoot generally more responsive than lucerne. © 1997 SCI.     

The effect of formalin and lower volatile fatty acids on silage fermentation

Lolium multiflorum was ensiled in 3 kg capacity PVC silos after treatment with formalin, formic acid, acetic acid and propionic acid applied singly and in mixtures of two, three and four at a constant application rate of 4.5 g kg^?1 fresh grass. The extent of fermentation was assessed by measuring pH, WSC, VN and TSN, and by microbiological analysis of total microorganisms and yeasts. The stability of the silages on exposure to air was measured using a specially constructed temperature recording apparatus. All additives restricted fermentation, although acetic acid and propionic acid were less effective than formalin, formic acid and mixtures of additives. The most aerobically stable silages were those treated with propionic acid, formic/acetic acids, and formic/acetic/propionic acids.     

Effect of the stage of growth,wilting and inoculation in field pea (Pisum sativum L.) silages. II. Nitrogen fractions and amino acid compositions of herbage and silage

The aim of the study was to investigate the effects of stage of maturity, wilting and inoculant application on proteolysis in field pea herbage and silage in northern Italy. Semi‐leafless field peas were harvested at four progressive morphological stages (end of flowering, I; beginning of pod filling, II; advanced pod filling, III; beginning of ripening, IV). For each stage of growth, the herbage was field wilted to a dry matter (DM) content around 330 g kg^?1. The unwilted and wilted herbages were ensiled with (I) and without (C) a lactic acid bacteria (LAB) inoculant. The stage of growth significantly affected all the nitrogen fraction concentrations both in herbage and in silage. Extensive proteolysis took place in silages made at early morphological stages and characterised by a high crude protein content (around 240 g kg^?1 DM), as shown by the non‐protein nitrogen (NPN) value (around 700 g kg^?1 total N or higher). Neither inoculum nor wilting helped to reduce the protein degradation in these silages. The level of proteolysis was reduced in silages made from the pod filling stage onwards where most of the protein was localised in the seed and a better fermentation pattern was observed. The amino acid (AA) composition of silages made at stage IV was close to that of fresh herbage, with minimal losses of nutritionally essential amino acids for ruminants. Copyright © 2006 Society of Chemical Industry