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8 4 1 Research Article Received: 16 December 2009 Revised: 15 October 2010 Accepted: 9 November 2010 Published online in Wiley Online Library: 24 December 2010 (wileyonlinelibrary.com) DOI 10.1002/jsfa.4255 Comparative evaluation of laboratory-scale silages using standard glass jar silages or vacuum-packed model silages Sandra Hoedtke and Annette Zeyner ∗ Abstract BACKGROUND: The objective of this study was to compare the fermentation variables of laboratory-scale silages made in glass pr
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   8  4 1  ResearchArticle Received: 16December 2009 Revised: 15 October 2010 Accepted: 9 November 2010 Published onlinein Wiley OnlineLibrary: 24 December 2010 (wileyonlinelibrary.com) DOI 10.1002/jsfa.4255 Comparativeevaluationoflaboratory-scalesilagesusingstandardglassjarsilagesorvacuum-packedmodelsilages SandraHoedtkeandAnnetteZeyner ∗ Abstract BACKGROUND:Theobjectiveofthisstudywastocomparethefermentationvariablesoflaboratory-scalesilagesmadeinglasspreservingjars(GLASS)andvacuum-packedplasticbags(Rostockmodelsilages,ROMOS).Silageswerepreparedfromperennialryegrass(freshandwilted,151gkg − 1 and286gkg − 1 drymatter(DM),respectively)andremoistenedcoarselygroundryegrain(650gkg − 1 DM) either with or without the addition of a lactic acid bacteria inoculant (3 × 10 5 colony forming units (cfu) g − 1 ,LAB).Quintuplicatesiloswereopenedondays2,4,8,49and90.RESULTS: Silage pH ( P   =  0 . 073), acetic acid content ( P   =  0 . 608) and ethanol content ( P   =  0 . 223) were not influenced by theensiling method. The contents of DM ( P   <  0 . 001) and propionic acid ( P   =  0 . 008) were affected by the ensiling method, butmeandifferenceswereonlymarginal.InROMOStheconcentrationoflacticacidwasincreased( P  = 0 . 007)whereasbutyricacidwasproducedless( P  = 0 . 001)whencomparedtoGLASS.ThissuggestedslightlybetterensilingconditionsforROMOS.CONCLUSIONS: ROMOS represents a reasonable alternative to glass jar silages and opens the possibility for furtherinvestigations,e.g.studyingtheimpactofpackingdensityaswellasthequantitativeandqualitativeanalysisoffermentationgases.c  2010SocietyofChemicalIndustryKeywords: laboratory-scale silage; glass jar; vacuum-packing; inoculant; perennial ryegrass; rye grain INTRODUCTION Rapid and cost-effective evaluation of the improvement of theforagepreservation,aswellasdeterminingtheefficacyofadditives(acids, enzymes or bacterial inoculants) requires studies of theensiling process at the laboratory scale. Although there are onlya limited number of publications, it has been assumed thatsmall-scale silos provide a reliable prediction of the farm-scalefermentation process. 1–3 Model silages have been used sincethe beginning of the 20th century, comprising different types of fixed-volume vessels like test tubes, 4 porcelain containers, 5 milk bottles 6 andglassjars 7 withdifferentcapacitiesrangingfrom50 gtoseveralkilograms.InGermany,followingtherecommendationsof the German Agricultural Society (DLG), glass preserving jarsare commonly used for studies on the fermentation processas well as for monitoring and evaluation of additives. 8 Despitebeing widely used, 9–11 the glass jar silage method has severaldisadvantages: Pre- and post-treatment are costly and time-consuming and require considerable extended storing space forthe jars. Depending on the operator there is a marked influenceon the packing density of the forage inside the glass and a highvariability within one vessel and between replications.Besides fixed-volume vessels, silages made in plastic bagshave also been examined. However, method procedures areheterogeneous and often a detailed description is not provided.Jones, 12 forinstance,describedsilagesofdifferentherbagesmadein polyethylene bags using a suction pump with a carbon dioxidefilled bag. More recentstudies report on sealed plastic bags usinga controlled vacuum of 0.2 bar. 13  The use of a household vacuumsealer 14,15 and a single-chamber vacuum-packaging machine 16 for sealing polyethylene bag silos have been described, but noinformationabouttheexperimentaldesignorthelevelofvacuumwas given in those studies. Hence, unlike ensilage trials withsilo containers like glass jars, results of plastic bag silages aredifficult to compare, depending on the experimental design.Moreover, no comparison with glass jar silages was made inthose studies. Johnson  etal  . 17 studied varying packing densitiesin vacuum-packed plastic bag silos by applying different initialvacuum settings and additionally compared results with glass jarsilages. They concluded that silages made in plastic bags providea reasonable alternative for glass vessels. However, it seems to bea shortcoming that the vacuum needed to achieve equal packingdensities in glass jars and plastic bags was only approximateand that the packing density of the forage decreased during thefermentation process. The disadvantages of the glass jar ensiling system made clearthat there is a demand for an adequate alternative for studying ∗ Correspondence to: AnnetteZeyner, Universit ¨ at Rostock, Agrar- und Umweltwissenschaftliche Fakult ¨ at, Professur f ¨ ur Ern¨ ahrungsphysiologie und Tierern¨ ahrung,Justus-von-Liebig-Weg8,18059Rostock,Germany.E-mail:annette.zeyner@uni-rostock.deUniversit ¨ at Rostock, Agrar- und Umweltwissenschaftliche Fakult ¨ at, Professur f ¨ urErn¨ ahrungsphysiologieundTierern¨ ahrung,18059Rostock,Germany   JSciFoodAgric   2011; 91 : 841–849 www.soci.org c  2010 Society of Chemical Industry   8  4 2   www.soci.org S Hoedtke, A Zeynerthe silage fermentation process. Ensiling in plastic pouches is afavourablemethod,asitdoesnothavethecommondrawbacksof glassjarsilages.Conversely,moreconsistentpackingdensitiesandahigherthroughputofsamplescanbeachievedusingplasticbagsilages.Toourknowledge,apartfromthestudiesofJohnson etal  . 17 thereisalackofinformationaboutcomparisonsofglassjarvesselsand vacuum-packed plastic bags used for ensiling. Therefore, theobjective of the present study was to establish Rostock modelsilages (ROMOS) as a method for model silages made in vacuum-packed plastic bags using the standardized method of glass jarsilages as a reference. Both model silage procedures were rununder identical conditions using the fermentation pattern andaerobic stability as criteria of comparison. MATERIALSANDMETHODS Studydesign Silages were made in glass jars (GLASS) and plastic bags (ROMOS)usingfreshperennialryegrassasharvested(FPR),wiltedperennialryegrass (WPR) and remoistened coarsely ground rye grain (RRG).GLASSandROMOSwerecarriedoutwithallplantmaterialsundersimilar conditions, with particular attention to identical packingdensities. Silages were made either with the addition of a lacticacid bacteria inoculant ( + LAB) or without additive ( − LAB) in fivereplications each. Silos were opened on days 2, 4, 8, 49 and90. Variables used to evaluate ensiling methods were pH value(all storage durations), fermentation products (2-day and 49-daysilages to characterize the early fermentation process and thestabilized silage)and aerobic stability (49-day silages). Plantmaterial Perennial ryegrass ( Lolium perenne ) was harvested from a puresward (fourth cut) at the early flowering stage using a cutter-bartype mower. Silages were made from fresh and wilted materialwithdrymatter(DM)contentsof151and286g kg − 1 ,respectively. The chopped grass (approximately 4 cm) was ensiled in glass jars(GLASS) as well as polyethylene bags (ROMOS) without (control)and with the addition of a lactic acid bacteria (LAB) inoculant( Lactobacillus plantarum , 3  ×  10 5 cfu g − 1 , BIO-SIL ® , Dr Pieper Technologie- und Produktentwicklung, Wuthenow, Germany).Rye grains ( Secale cereale ) with a DM content of 881 g kg − 1 werecoarselygroundinachopper(meshsize4 mm).Thecoarselygroundryegrainswereremoistenedbyaddingdeionizedwatertoa calculated DM content of 650g kg − 1 . Model silages were madein GLASS as well as in ROMOS without additive (control) or withaddition of LAB inoculant applied at the rate mentioned above. Glassjarsilages(GLASS  ) Glass jars (1.5 L volume) were washed and sterilized (180 ◦ C, 8 h)before use. The jar was filled with herbage according to DLGrecommendations, 8 at a preferable pore volume of 4 L kg − 1 DM.For silages made of FPR (151 g kg − 1 DM), 681 g were packed intothe glass jar and compressed by hand with the aid of a rod,representing a final packing density of 0.45 g cm − 3 . Respectively513 gofWPR(286 g kg − 1 DM)werefilled into thejars, resultingina packing density of 0.34g cm − 3 . As there are no recommendedfillingquantitiesestablishedforRRG,thismaterialwaspackedintothe entire jar, only providing 0.5 cm of unfilled space to the lid.Finally, a sample weight of 1500 g was determined for RRG whichresulted in a packing density of 1 g cm − 3 . Jars were closed with arubber-lined lid that was fixed using metal clips. Glass jars of allplant materials and treatments were stored in a tempered roomat 25 ◦ C and opened on days 2, 4, 8, 49 and 90. Vacuum-packedRostockmodelsilages(ROMOS) For ROMOS vacuum-packed plastic bag silages a vacuum sealer(V.300, LAVA vacuum-package, Bad Saulgau, Germany) was used.Four-hundred grams of FPR or WPR as well as RRG were placed inpolyethylenebags(PA-PE20/70,200mm × 300 mm,LAVAvacuumpackage,BadSaulgau,Germany).Thebagshadagaspermeabilityat23 ◦ Cand0%relativehumidityof50,150and10cm 3 m − 2 d − 1 foroxygen,carbondioxideandnitrogen,respectively. 18  Therequiredvacuum for ROMOS was obtained by a volumetric measurementoftheair-evacuatedplasticbags.Accordingtothesampleweight,thevacuumhadtobesetsoastorealizeabagvolumeof889(FPR),1176(WPR) and 400(RRG) cm 3 inorder toobtain a correspondingpacking density comparable to GLASS of 0.45, 0.34 and 1 g cm − 3 ,respectively. Silage material was pre-compressed by hand beforethe bags were air-evacuated and heat-sealed.In order to preventdeformation of ROMOS bags, adhesive tapewas wrapped around the sealed polyethylene bags. Thereby carehadtobetakenthattheshapewasstabilizedwithoutthepackingdensity being increased. To avoid bloating, the wrapped bag waspuncturedwithaninjectionneedle(2 × 50 mm,RometschGmbH,Heilbronn, Germany), which was disinfected after each bag with70% ethanol, and put immediately into a second bag (PA-PE20/70, 300 mm × 500mm, LAVA vacuum package, Bad Saulgau,Germany) which was air-evacuated with the same vacuum andsealed at once to maintain anaerobic conditions. ROMOS silageswere stored under the same conditions and opened on the samedays as GLASS. Chemicalanalyses A representative sample of the chopped herbage and coarselyground rye grains was freeze-dried and milled to 1 mm mesh size(Brabender, Duisburg, Germany). Of the lyophilized samples, DMwas determined byoven drying at 105 ◦ C for 3 h. Ashing followedat 600 ◦ C for 5 h in a muffle furnace. Crude protein (N × 6.25) wasanalysedwithKjeldathermandVapodest(Gerhardt,K ¨onigswinter,Germany). 19 Neutral detergent fibre (exclusive residual ash) andacid detergent fibre (exclusive residual ash) were determined bywet chemical analyses 20 and crude fibre 21 using a FOSS analyser(Fibertec2010,Rellingen,Germany).Water-solublecarbohydrates(WSC) were analysed as monomeric and dimeric sugars as wellas fructans in water extracts (1 h at 25 ◦ C) by high-performanceliquid chromatography (HPLC) (HPX-87C, Biorad, Hercules, CA,USA) according to Menge-Hartmann  etal  ., 22 with a flow rate of 0.65 mL min − 1 at refractive index detector (column temperature80 ◦ C). For determination of starch an enzymatic procedureusing amylase (Thermamyl 120, Novo Nordisk A/S, Denmark)was chosen. 23 Concentration of glucose was measured by HPLCwith the conditions mentioned before and the starch contentwas calculated by considering the previously determined water-soluble carbohydrate content (glucose). Buffering capacity wasanalysed by titration with lactic acid (0.1 mol L − 1 ) to a pH of 4.0. 24 Silage DM was determined by drying to a constant weight(105 ◦ C, 17.5h). The pH value was measured potentiometricallyeach day the silage was opened, using a calibrated pH analyserwith glass and reference electrodes (precision 0.01, temperaturecompensation0–70 ◦ C).Forthispurposesilageextractswerepre-pared with 50 gsilageand 200 mLdeionized water.Fermentationproducts were analysed in the filtrated extracts (2-day and 49-day wileyonlinelibrary.com/jsfa  c  2010 Society of Chemical Industry  JSciFoodAgric   2011; 91 : 841–849   8  4  3   Evaluation of silages using standard glass jar silages or vacuum-packed model silages www.soci.orgsilages). Lactic acid was determined by HPLC (Aminex HPX-87H,Biorad) with a flow rate of 0.60mL min − 1 at the UV detector.Short-chain fatty acids and ethanol were quantitatively separatedby gas chromatography (GC-14A, CLASS-VP, Shimadzu, Kyoto,Japan).Nitrogenwasusedascarriergasatapressureof1 kg cm − 2 . Thetemperatureoftheinjectorandflameionizationdetectorwaskeptconstantat190 ◦ Ceach;thetemperatureofthecolumnovenwas programmed at 110 ◦ C during the first 1.5 min, increasing to170 ◦ C at a rate of 12 ◦ C min − 1 thereafter. Aerobicstability Aerobic stability was measured at day 49 of ensiling by means of temperature rise. 25 Silage samples representing 100 g DM wereput into plastic containers (1.25 L capacity), of which the base aswell as the lid were provided with a hole of 1 cm diameter. Athermocouple was fixed in the geometrical centre of the sampleand the closed test container was put into a cylinder made of Styrofoam. Temperature was measured at intervals of 6 h for7 days and recorded by data logger software (Version 4.2, PSES Electronics Services, Nieuwendijk, Netherlands). Silages wereconsideredasaerobicallyunstableifthetemperatureofthesilagesample and the room temperature (set at 20 ◦ C) differed by morethan 3 ◦ C. Statisticalanalysis ResultswereanalyzedbySPSS15.0computerprogram(SPSS15.0 c  for Windows; SPSS Inc., Chicago, IL, USA). Analysis of variance(ANOVA) was performed to investigate the effects of the mainfactors ‘method’ (GLASS and ROMOS), ‘silage material’ (FPR, WPRand RRG), ‘inoculation’ ( − LAB and + LAB), and ‘storage duration’(for pH: 2, 4, 8, 49 and 90 days; for fermentation products: 2 and49 days)aswellastherespectiveinteractions.ResultsfromANOVAweregivenasmean ± pooledSD,wherebypooledSDisthesquareroot of mean square residue. Multiple comparison of means wasdone by applying the Student–Newman–Keuls test. For mostvariablestherewasasignificant( P  < 0 . 05)interactionbetweenallincluded main factors. Therefore, regarding each silage material,means ( ± SD) were additionally calculated for GLASS and ROMOSwithin the individual steps of the other factors (’inoculation’  × ‘storage duration’) and compared by paired Student’s  t  -tests.Differences of means for aerobic stability between GLASS andROMOS were also analysed by paired Student’s  t  -test. The level of significance was preset at  P  < 0 . 05. RESULTS  The WSCofthe perennial ryegrassbeforewilting and the coarselyground rye grain before remoistening were 105 and 58 g kg − 1 DM, respectively (Table 1). Comparatively favourable ensilingconditions were observed with the perennial ryegrass, with abufferingcapacity(BC)of69 glacticacid1 Kg − 1 DM(WSC/BCratio1.5). Due to a rather high content of fructans and a BC of only15 g lactic acid 1 Kg − 1 , rye grains showed a WSC/BC ratio of 3.9,suggesting excellent ensilability characteristics. The technique of model silages had a significant influenceon the DM ( P   <  0 . 001), whereas there was only a marginaldifferencebetweenoverallmeanvaluesofGLASSwith343 g kg − 1 DM and ROMOS with 346g kg − 1 DM (Table 2) without biologicalrelevance. While within treatments there were differences of DMbetween ensiling methods, these did not seem to follow anypattern and were considered to be random in all silage materials Table1.  Chemical characterization of perennial ryegrass and ryegrains usedfor ensilingPerennialryegrass Rye grainsDry matter (g kg − 1 ) 151 881Crude ash (g kg − 1 DM) 114 18Crude protein (g kg − 1 DM) 131 94Neutral detergentfibre (g kg − 1 DM) 457 141Acid detergentfibre (g kg − 1 DM) 269 34Crude fibre (g kg − 1 DM) 244 29WSC (g kg − 1 DM) 105 58Starch (g kg − 1 DM) ND 692Buffering capacity(g LA 1 Kg − 1 DM) 69 15DM, dry matter; LA, lactic acid; ND, not detected; WSC, water-solublecarbohydrates. (Tables 3 and 4). However, fermentation losses were significantlyhigher ( P   =  0 . 014) in ROMOS than in GLASS, being an averageof 12.9g kg − 1 and 10.2 g kg − 1 sample weight, respectively (datanot shown). There was a method  ×  silage interaction on theDM ( P   =  0 . 003) and multiple interactions except for method  × inoculation x storage duration ( P  = 0 . 084). ThepHofsilageswasnotinfluencedbythemethod( P  = 0 . 073),being 4.43 for GLASS and 4.40 for ROMOS, but was affectedby the silage material ( P   <  0 . 001), inoculation ( P   <  0 . 001) andstorageduration( P  < 0 . 001).Withinsingletreatmentsandstoragedurations of the silage material differences of pH ( P   < 0 . 05) wereobserved only randomly and were considered to be generallylow (Table 5). Interactions were observed for method  ×  silage( P   <  0 . 001), method  ×  storage duration ( P   <  0 . 001) and allmultiple interactions except method  ×  silage  ×  inoculation  × storage duration ( P  = 0 . 370).Lactic acid was the primary acid in GLASS as well as inROMOS; however, the overall lactic acid content was significantlyhigher ( P   <  0 . 007) in ROMOS (64.3 g kg − 1 DM) than in GLASS(58.6 g kg − 1 DM). This was especially the case for FPR and WPR inboth inoculation treatments, as vacuum-packed silages showedpredominantly higher lactic acid contents at days 2 and 49 of opening (Table 3). However, significant differences between theensiling methods were only found at few storage durations orinoculation treatments and can thus be seen as randomized.ROMOS silages of RRG showed lower lactic acid contents thanGLASSsilages,butdifferences( P  < 0 . 05)couldbeobservedinonlysome treatments. Apart from the storage duration ( P   =  0 . 800),silage material ( P   <  0 . 001) and inoculation ( P   <  0 . 001) hadsignificanteffectson thelacticacid content. Interactionsbetweenthe ensiling method and the plant material, inoculation andstorage duration as well as method × silage × storage and silage × inoculation × storage duration were observed.Whiletherewasnosignificanteffectoftheensilingtechniqueontheaceticacidcontent( P  = 0 . 608),thesilagematerial( P  < 0 . 001)aswellasinoculation( P  < 0 . 001)andstorageduration( P  < 0 . 001)influenced the formation of acetic acid. There was a method  × inoculation × storagedurationandsilage × inoculation × storageduration interaction. The average propionic acid content differedsignificantly ( P   =  0 . 008) between GLASS and ROMOS, althoughdifferences were only marginal. Moreover, of all prepared silages,propionicacidwasonlypresentinFPR( + LABand − LAB)andWPR( − LAB) at day 49 of opening (Table 3), and only in FPR ( − LAB)was a significant difference ( P   <  0 . 05) observed. There were  JSciFoodAgric   2011; 91 : 841–849 c  2010 Society of Chemical Industry  wileyonlinelibrary.com/jsfa   8  4 4  www.soci.org S Hoedtke, A Zeyner Table2.  Mean and pooled SD of DM, pH value and content of fermentation products and  P  -values for variance factors silage, method, inoculationand storage duration andthe respectiveinteractionspotentially influencing DM, pH value and concentrationsoffermentation productsDM(g kg − 1 ) pHLA(g kg − 1 DM)AA(g kg − 1 DM)PA(g kg − 1 DM)BA(g kg − 1 DM)Ethanol(g kg − 1 DM)Method GLASS 343b 4.43 58.6b 7.5 0.9a 16.6a 9.1ROMOS 346a 4.40 64.3a 7.7 0.6b 13.6b 9.4Silage FPR 134c 4.40b 87.5a 12.8a 1.2a 25.3a 11.9aWPR 265b 4.52a 80.0b 8.9b 1.1b 20.1b 8.7bRRG 634a 4.32c 16.9c 1.2c ND ND 7.2cInoculation  − LAB 341b 4.71a 48.9b 6.7b 1.2a 22.1a 10.1a + LAB 347a 4.12b 74.1a 8.5a 0.3b 8.1b 8.4bStorage duration 2 days 355a 4.52a 61.7 8.9a ND ND 7.8b4 days 350b 4.32c NA NA NA NA NA8 days 346c 4.34c NA NA NA NA NA49 days 337d 4.39b 61.2 6.4b 1.5 30.3 10.7a90 days 334e 4.49a NA NA NA NA NAPooledSD 4.55 0.118 11.5 1.90 0.71 4.97 1.58 P  -valueMethod  < 0.001 0.073 0.007 0.608 0.008 0.001 0.223Silage  < 0.001  < 0.001  < 0.001  < 0.001  < 0.001  < 0.001  < 0.001Inoculation  < 0.001  < 0.001  < 0.001  < 0.001  < 0.001  < 0.001  < 0.001Storage duration  < 0.001  < 0.001 0.800  < 0.001  < 0.001  < 0.001  < 0.001Method × silage 0.003  < 0.001  < 0.001 0.897 0.093 0.001 0.012Method × inoculation 0.986 0.610 0.019 0.292  < 0.001 0.001 0.011Method × storage duration 0.065  < 0.001 0.019 0.225 0.008 0.001 0.019Method × silage × storage duration 0.002 0.015  < 0.001 0.223 0.093 0.001  < 0.001Method × inoculation × storage duration 0.084 0.034 0.057 0.025  < 0.001 0.001 0.134Silage × inoculation × method 0.038  < 0.001 0.057 0.249  < 0.001 0.027  < 0.001Silage × inoculation × storage duration  < 0.001  < 0.001  < 0.001 0.005  < 0.001  < 0.001  < 0.001Method × silage × inoculation × storageduration 0.007 0.370 0.269 0.067  < 0.001 0.027 0.029AA, acetic acid; BA, butyric acid; GLASS, glass jar silage; FPR, fresh perennial ryegrass; LA, lactic acid; − LAB, without additive; + LAB, with actic acidbacteriainoculant;NA, notanalysed;ND, notdetected;PA,propionicacid;ROMOS,vacuum-packedRostockmodelsilage;RRG, remoistenedcoarselyground rye grain; WPR, wilted perennialryegrass.Entries followedby differentletters indicate significantly differentmeans( P  < 0 . 05). interactions except for method × silage and method × silage × storage duration.Butyric acid was detected only in 49-day silages for bothinoculation treatments of FPRand WPR, but in none of the silagesofRRG.Theformationofbutyricacidwasinfluencedbytheensilingmethod ( P  = 0 . 001), with higher average contents in GLASS thanin ROMOS, and by the silage material ( P   <  0 . 001), inoculation( P   <  0 . 001) and storage duration ( P   <  0 . 001). Interactions wereobserved.Ethanol occurred in all model silages and its content was influ-enced significantly by the silage material, inoculation treatmentand storage duration ( P   <  0 . 001 each), whereas the techniqueof model silages had no effect on the formation of ethanol( P   =  0 . 223). There were interactions except for method × inocu-lation × storage duration.Aerobic deterioration was found in ROMOS of FPR with LABinoculant as well as in GLASS of WPR without additive. In thosetreatments four of five repetitions were aerobically stable and inonlyone sample of eachtreatment the temperature rose by morethan 3 ◦ C above the reference room temperature of 20 ◦ C after1.8 and 2.0 days, respectively, resulting in meanvalues of 6.0 daysof aerobic stability (Fig. 1). The silages of RRG with addition of LAB inoculant showed the lowest aerobic stability in both GLASS(mean4.8 days)andROMOS(mean5.5 days)silages.Nevertheless,in all treatments no significant differences between GLASS andROMOS silages were verified ( P  > 0 . 05). DISCUSSION  The aim of this study was to compare the model silage systemsof glass jars and vacuum-packed ROMOS as an alternative forcommonly used fixed-volume silo vessels. Minor measurableeffects of the ensiling technique (GLASS and ROMOS) on the DMwere considered to be irrelevant since only sporadic significantdifferences between the ensiling methods were observed withsingle treatments. Significantly higher DM losses were foundin plastic bags compared to glass jars, but were thought notto be of biological significance. Unless the fermentation is notentirely homolactic, 26 fermentation losses are likely to take place.As ROMOS showed losses in the range of GLASS, air-evacuatedplastic bags consequently fulfil the demands of common airtightsilo vessels. The silages of FPR showed a rise in pH from day 49 to day 90in both GLASS and ROMOS. A rise in pH indicates badly preservedsilages, with either enterobacteria or clostridia dominating thefermentation. Presumably they are made from crops whichcontain low levels of fermentable carbohydrates, which showonlyinsufficientnumbersofepiphyticlacticacidbacteriaorwhichare ensiled too wet, 2 the latter being probably the case for the wileyonlinelibrary.com/jsfa  c  2010 Society of Chemical Industry  JSciFoodAgric   2011; 91 : 841–849
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