The effects of fermentation acids on bacterial growth

Anaerobic habitats often have low pH and high concentrations of fermentation acids, and these conditions can inhibit the growth of many bacteria. The toxicity of fermentation acids at low pH was traditionally explained by an uncoupling mechanism. Undissociated fermentation acids can pass across the cell membrane and dissociate in the more alkaline interior, but there is little evidence that they can act in a cyclic manner to dissipate protonmotive force. Fermentation acid dissociation in the more alkaline interior causes an accumulation of the anionic species, and this accumulation is dependent on the pH gradient (delta pH) across the membrane. Fermentation acid-resistant bacteria have low delta pH and are able to generate ATP and grow with a low intracellular pH. Escherichia coli O157:H7 is able to decrease its intracellular pH to 6.1 before growth ceases, but this modest decrease in delta pH can only partially counteract the toxic effect of fermentation anion accumulation. Fermentation acid-resistant bacteria are in most cases Gram-positive bacteria with a high intracellular potassium concentration, and even acid-sensitive bacteria like E. coli K-12 have increased potassium levels when fermentation acids are present. Intracellular potassium provides a counteraction for fermentation acid anions, and allows bacteria to tolerate even greater amounts of fermentation anions. The delta pH-mediated anion accumulation provides a mechanistic explanation for the effect of fermentation acids on microbial ecology and metabolism.

Effect of applying lactic acid bacteria isolated from forage crops on fermentation characteristics and aerobic deterioration of silage

Two selected strains, Lactobacillus casei FG 1 and Lactobacillus plantarum FG 10 that were isolated from forage crops were used as additives at 1.0 x 10(5) cfu/g of fresh matter to alfalfa, Italian ryegrass, and sorghum, and their effect on fermentation characteristics and aerobic deterioration of silage was studied. The three silages treated with strains FG 1 or FG 10 were well preserved; had significantly lower pH values, butyric acid, propionic acid, and ammonia N concentrations, gas production, and dry matter losses; and had significantly higher contents of residual water-soluble carbohydrates and lactic acid than did the respective control silages. Yeast counts were high in all treated silages and increased rapidly during aerobic exposure. As a result, treated silages spoiled faster upon aerobic exposure than did the respective control silages. Most yeasts isolated from deteriorated silages showed high tolerance to lactic acid but low tolerance to butyric acid, and they were able to grow at low pH conditions and assimilate lactic acid. The results confirmed that L. casei and L. plantarum improved fermentation quality but did not inhibit the growth of silage yeast or aerobic deterioration of the silage.

Isolation and characterization of two exopolysaccharides produced by Lactobacillus plantarum EP56

A Lactobacillus plantarum strain producing exopolysaccharides (EPSs) was isolated from corn silage. When this strain, named L. plantarum EP56, was grown on a chemically defined medium, two EPS fractions were isolated. The cell-bound EPS fraction (EPS-b) was composed of a single high-molecular-mass polymer of 8.5x10(5) Da containing glucose, galactose and N-acetylgalactosamine in a molar ratio of approximately 3:1:1 and traces of glycerol and phosphoglycerol. The released EPS fraction (EPS-r) was composed of the high-molecular-mass bound polysaccharide and a second polymer of 4x10(4) Da containing glucose, galactose and rhamnose in a molar ratio of 3:1:1 and traces of glycerol and phosphoglycerol. EPS-b and EPS-r contained phosphate which contributes to their negative net charge. Studies on polysaccharide production and location showed that both polymers were synthesized during the exponential growth phase and that the EPS-b polymer was progressively released into the culture medium during the stationary growth phase. Carbon source and temperature influenced EPS synthesis when L. plantarum EP56 was grown in a chemically defined medium. Lactose was the most efficient carbon source among the five tested (glucose, galactose, fructose, lactose and sucrose). EPS production was also increased when the incubation temperature is lowered.

Lactobacillus diolivorans sp. nov., a 1,2-propanediol-degrading bacterium isolated from aerobically stable maize silage

Inoculation of maize silage with Lactobacillus buchneri (5 x 10(5) c.f.u. g(-1) of maize silage) prior to ensiling results in the formation of aerobically stable silage. After 9 months, lactic acid bacterium counts are approximately 10(10) c.f.u. g(-1) in these treated silages. An important subpopulation (5.9 x 10(7) c.f.u. g(-1)) is able to degrade 1,2-propanediol, a fermentation product of L. buchneri, under anoxic conditions to 1-propanol and propionic acid. From this group of 1,2-propanediol-fermenting, facultatively anaerobic, heterofermentative lactobacilli, two rod-shaped isolates were purified and characterized. Comparative 16S rDNA sequence analysis revealed that the newly isolated bacteria have identical 16S rDNA sequences and belong phylogenetically to the L. buchneri group. DNA-DNA hybridizations, whole-cell protein fingerprinting and examination of phenotypic properties indicated that these two isolates represent a novel species, for which the name Lactobacillus diolivorans sp. nov. is proposed. The type strain is LMG 19667T (= DSM 14421T).

A Meta-Analysis of the Effects of Lactobacillus buchneri on the Fermentation and Aerobic Stability of Corn and Grass and Small-Grain Silages

The results of adding Lactobacillus buchneri to silages from 43 experiments in 23 sources reporting standard errors were summarized using meta-analysis. The effects of inoculation were summarized by type of crop (corn or grass and small grains) and the treatments were classified into the following categories: 1) untreated silage with nothing applied (LB0), 2) silage treated with L. buchneri at < or = 100,000 cfu/g of fresh forage (LB1), and 3) silage treated with L. buchneri at > 100,000 cfu/g (LB2). In both types of crops, inoculation with L. buchneri decreased concentrations of lactic acid, and this response was dose-dependent in corn but not in grass and small-grain silages. Treatment with L. buchneri markedly increased the concentrations of acetic acid in both crops in a dose-dependent manner. The numbers of yeasts were lower in silages treated with LB1 and further decreased in silages treated with LB2 compared with untreated silages. Untreated corn silage spoiled after 25 h of exposure to air but corn silage treated with LB1 did not spoil until 35 h, and this stability was further enhanced to 503 h with LB2. In grass and small-grain silages, yeasts were nearly undetectable; however, inoculation improved aerobic stability in a dose-dependent manner (206, 226, and 245 h for LB0, LB1, and LB2, respectively). The recovery of DM after ensiling was lower for LB2 (94.5%) when compared with LB0 (95.5%) in corn silage and was lower for both LB1 (94.8%) and LB2 (95.3%) when compared with LB0 (96.6%) in grass and small-grain silages.

The role of Lactobacillus buchneri in forage preservation

In 1996 Wienberg and Muck proposed to implement Lactobacillus buchneri in silage starters. The main reason for the use of heterofermentative lactic acid bacteria is the increased stability of silages against deterioration by yeasts and moulds when exposed to air. In the following years, the unique activity of L. buchneri in silages was evaluated. It was proven that acetic acid formed from lactic acid by L. buchneri is solely responsible for the increased stability of silages. Recently, a novel metabolic pathway from lactic acid to acetic acid and 1,2-propanediol was proposed.

Phylogenetic diversity of lactic acid bacteria associated with paddy rice silage as determined by 16S ribosomal DNA analysis

A total of 161 low-G+C-content gram-positive bacteria isolated from whole-crop paddy rice silage were classified and subjected to phenotypic and genetic analyses. Based on morphological and biochemical characters, these presumptive lactic acid bacterium (LAB) isolates were divided into 10 groups that included members of the genera Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Pediococcus, and WEISSELLA: Analysis of the 16S ribosomal DNA (rDNA) was used to confirm the presence of the predominant groups indicated by phenotypic analysis and to determine the phylogenetic affiliation of representative strains. The virtually complete 16S rRNA gene was PCR amplified and sequenced. The sequences from the various LAB isolates showed high degrees of similarity to those of the GenBank reference strains (between 98.7 and 99.8%). Phylogenetic trees based on the 16S rDNA sequence displayed high consistency, with nodes supported by high bootstrap values. With the exception of one species, the genetic data was in agreement with the phenotypic identification. The prevalent LAB, predominantly homofermentative (66%), consisted of Lactobacillus plantarum (24%), Lactococcus lactis (22%), Leuconostoc pseudomesenteroides (20%), Pediococcus acidilactici (11%), Lactobacillus brevis (11%), Enterococcus faecalis (7%), Weissella kimchii (3%), and Pediococcus pentosaceus (2%). The present study, the first to fully document rice-associated LAB, showed a very diverse community of LAB with a relatively high number of species involved in the fermentation process of paddy rice silage. The comprehensive 16S rDNA-based approach to describing LAB community structure was valuable in revealing the large diversity of bacteria inhabiting paddy rice silage and enabling the future design of appropriate inoculants aimed at improving its fermentation quality.

Comparative denaturing gradient gel electrophoresis analysis of fungal communities associated with whole plant corn silage

Significant portions of grain produced for livestock consumption are convened into ensiled forage. Silage producers have long recognized the positive effects of using an inoculant to insure the proper transformation of forage into a palatable and digestible feedstuff. When silage is fed from a storage structure, exposure to air stimulates the growth of epiphytic aerobes that may result in the loss of up to 50% of the dry matter. Moreover, fungi have been found to be associated with ensiled forage, but their growth is normally suppressed by the anaerobic conditions. However, the introduction of oxygen results in a fungal bloom, and the fungi and the associated metabolites may result in lost productivity in the livestock consuming the contaminated forage. In this study, we report on the diversity of the fungal community associated with whole plant corn silage during the ensiling process, and the effect of two different bacterial inoculants as compared with the uninoculated natural epiphytic fermentation on the distribution of the fungi associated with the silage. The fungal community from duplicate mini-silo packages of the same treatment was analyzed by denaturing gradient gel electrophoresis and direct sequencing of the resulting operational taxonomic units. This method proved useful in analyzing the complex microbial communities associated with the forage in that it was possible to determine that one inoculant dramatically influenced the fungal community associated with whole plant corn silage.

Mycoflora and multimycotoxin detection in corn silage: experimental study

Agricultural activities involve the use of crop preservation such as "trench-type" silo, which can sometimes be contaminated by fungi. To investigate the exposure of livestock and farm workers to fungal spores and mycotoxins, a multimycotoxin analysis method has been developed. Six mycotoxins (aflatoxin B1, citrinin, deoxynivalenol, gliotoxin, ochratoxin A, and zearalenone) were quantified by high-performance liquid chromatography coupled to mass spectrometry after solid-phase extraction. An experimental study of fungal species and mycotoxins was conducted in corn silage (Normandy, France) during 9 months of monitoring. The results indicated the recurrence of around 20 different species, with some of them being potentially toxigenic fungi such as Aspergillus fumigatus, Aspergillus parasiticus, Fusarium verticillioides, and Monascus ruber, and the detection of aflatoxin B1 (4-34 ppb), citrinin (4-25 ppb), zearalenone (23-41 ppb), and deoxynivalenol (100-213 ppb). This suggested a possible chronic exposure to low levels of mycotoxins.

The impact of the quality of silage on animal health and food safety: a review

This paper reviews the microbiological aspects of forage preserved by ensilage. The main principles of preservation by ensilage are a rapid achievement of a low pH by lactic acid fermentation and the maintenance of anaerobic conditions. The silage microflora consists of beneficial micro-organisms, i.e. the lactic acid bacteria responsible for the silage fermentation process, and a number of harmful micro-organisms that are involved in anaerobic or aerobic spoilage processes. Micro-organisms that can cause anaerobic spoilage are enterobacteria and clostridia. Clostridium tyrobutyricum is of particular importance because of its ability to use lactic acid as a substrate. Silage-derived spores of C. tyrobutyricum can cause problems in cheese making. Aerobic spoilage of silage is associated with penetration of oxygen into the silage during storage or feeding. Lactate-oxidizing yeasts are generally responsible for the initiation of aerobic spoilage. The secondary aerobic spoilage flora consists of moulds, bacilli, listeria, and enterobacteria. Mycotoxin-producing moulds, Bacillus cereus, and Listeria monocytogenes in aerobically deteriorated silage form a serious risk to the quality and safety of milk and to animal health.

Genotypic and phenotypic characterization of Lactobacillus casei strains isolated from different ecological niches suggests frequent recombination and niche specificity

Lactobacillus casei strains are lactic acid bacteria (LAB) that colonize diverse ecological niches, and have broad commercial applications. To probe their evolution and phylogeny, 40 L. casei strains were characterized; the strains included isolates from plant materials (n=9), human gastrointestinal tracts (n=7), human blood (n=1), cheeses from different geographical locations (n=22), and one strain of unknown origin. API biochemical testing identified niche-specific carbohydrate fermentation profiles. A multilocus sequence typing (MLST) scheme was developed for L. casei. Partial sequencing of six housekeeping genes (ftsZ, metRS, mutL, nrdD, pgm and polA) revealed between 11 (nrdD) and 20 (mutL) allelic types, as well as 36 sequence types. Phylogenetic analysis of MLST data by Reticulate and split decomposition analysis indicated frequent intra-species recombination. Purifying selection was detected, and is likely to have contributed to the evolution of certain L. casei genes. Pulsed-field gel electrophoresis (PFGE) using SfiI was able to discriminate all the isolates, even those not differentiated by MLST. Phylogenetic trees reconstructed based on the MLST data using minimum evolution algorithm, and the SfiI-PFGE restriction patterns using the unweighted-pair group method with arithmetic mean (UPGMA), revealed consensus clusters of strains specific to cheese and silage. Topological discrepancies between the MLST and PFGE trees were also observed, suggesting that intragenic point mutations have accumulated at a slower rate than indels and genome rearrangements in L. casei. The L. casei population analysed in this study demonstrated both a high level of phenotypic and genotypic diversity, as well as specificity to different ecological niches.

Metabolite profiles of lactic acid bacteria in grass silage

The metabolite production of lactic acid bacteria (LAB) on silage was investigated. The aim was to compare the production of antifungal metabolites in silage with the production in liquid cultures previously studied in our laboratory. The following metabolites were found to be present at elevated concentrations in silos inoculated with LAB strains: 3-hydroxydecanoic acid, 2-hydroxy-4-methylpentanoic acid, benzoic acid, catechol, hydrocinnamic acid, salicylic acid, 3-phenyllactic acid, 4-hydroxybenzoic acid, (trans, trans)-3,4-dihydroxycyclohexane-1-carboxylic acid, p-hydrocoumaric acid, vanillic acid, azelaic acid, hydroferulic acid, p-coumaric acid, hydrocaffeic acid, ferulic acid, and caffeic acid. Among these metabolites, the antifungal compounds 3-phenyllactic acid and 3-hydroxydecanoic acid were previously isolated in our laboratory from liquid cultures of the same LAB strains by bioassay-guided fractionation. It was concluded that other metabolites, e.g., p-hydrocoumaric acid, hydroferulic acid, and p-coumaric acid, were released from the grass by the added LAB strains. The antifungal activities of the identified metabolites in 100 mM lactic acid were investigated. The MICs against Pichia anomala, Penicillium roqueforti, and Aspergillus fumigatus were determined, and 3-hydroxydecanoic acid showed the lowest MIC (0.1 mg ml(-1) for two of the three test organisms).

Identification of Lactobacillus isolates from the gastrointestinal tract, silage, and yoghurt by 16S-23S rRNA gene intergenic spacer region sequence comparisons

Lactobacillus isolates were identified by PCR amplification and sequencing of the region between the 16S and 23S rRNA genes (spacer region). The sequences obtained from the isolates were compared to those of reference strains held in GenBank. A similarity of 97.5% or greater was considered to provide identification. To check the reliability of the method, the V2-V3 region of the 16S rRNA gene was amplified and sequenced in the case of isolates whose spacer region sequences were less than 99% similar to that of a reference strain. Confirmation of identity was obtained in all instances. Spacer region sequencing provided rapid and accurate identification of Lactobacillus isolates obtained from gastrointestinal, yoghurt, and silage samples. It had an advantage over 16S V2-V3 sequence comparisons because it distinguished between isolates of Lactobacillus casei and Lactobacillus rhamnosus.

Hydrolysis and microbial community analyses in two-stage anaerobic digestion of energy crops

AIMS

The roles of the diverse populations of micro-organisms responsible for biodegradation of organic matter to form methane and carbon dioxide are rudimentarily understood. To expand the knowledge on links between microbial communities and the rate limiting, hydrolytic stage of two-stage biogas production from energy crops, this study was performed.

METHODS AND RESULTS

The process performance and microbial communities (as determined by fluorescence in situ hybridization) in two separate two-stage batch digestions of sugar beets and grass/clover were studied. The microbial populations developed in the hydrolytic stage of anaerobic digestion of beets and grass/clover showed very few similarities, despite that the hydrolysis dynamics were similar. In both substrates, the solubilization of organic material was rapid for the first 10 days and accompanied by a build-up of volatile fatty acids (VFAs) and lactate. Between days 10 and 15, VFA and lactate concentrations decreased, as did the solubilization rates. For both substrates, Archaea started to appear in the hydrolytic stage between days 10 and 15, and the fraction of Bacteria decreased. The major bacterial group detected in the leachate fraction for beets was Alphaproteobacteria, whereas for grass/clover it was Firmicutes. The number of cells that bound to probes specifically targeting bacteria with cellulolytic activity was higher in the digestion of grass than in the digestion of beet.

CONCLUSIONS

This study allowed the identification of the general bacterial groups involved, and the identification of a clear shift in the microbial population when hydrolysis rate became limiting for each of the substrates investigated.

SIGNIFICANCE AND IMPACT OF THE STUDY

The findings from this study could be considered as a first step towards the development of strategies to stimulate hydrolysis further and ultimately increasing the methane production rates and yields from reactor-based digestion of these substrates.

The Effects of Various Antifungal Additives on the Fermentation and Aerobic Stability of Corn Silage

In 2 consecutive years, whole plant corn was ensiled in laboratory silos to investigate the effects of various silage additives on fermentation, dry matter (DM) recovery and aerobic stability. In yr 1, chopped forage was treated with 1) no additive (untreated, U), 2) Lactobacillus buchneri 40788, 4 x 10(5) cfu/g of fresh forage (LLB4), 3) L. buchneri 11A44, 1 x 10(5) cfu/g (PLB), 4) Biomax 5 (Lactobacillus plantarum PA-28 and K-270), 1 x 10(5) cfu/g (B5), 5) Silo Guard II (sodium metabisulfite and amylase), 0.05% of fresh forage weight (SG), 6) a buffered propionic acid-based additive, 0.1% (Ki-112), 7), sodium benzoate, 0.1% of fresh weight (SB), or 8) potassium sorbate:EDTA (1:1), 0.1% of fresh weight (PSE). Silage treated with LLB4 had the highest concentration of acetic acid compared with other treatments, and yeasts were undetectable in LLB4 (<log2 cfu/g). Silages treated with SB and PSE had the highest concentrations of water-soluble carbohydrates, the greatest recoveries of DM, and the lowest concentrations of ethanol. Silages treated with B5, SG, and Ki-112 had no effects on fermentation, DM recovery, or aerobic stability. The aerobic stabilities of silages treated with LLB4, SB, and PSE were greatest among all treatments. In yr 2, treatments were: 1) U, 2) LLB4, 3) PLB, 4) PLB at 4 x 10(5) cfu/g (PLB4), and 5) B5. Silages treated with L. buchneri had greater concentrations of acetic acid but lower concentrations of ethanol than did U- and B5-treated silages. Yeasts were undetected in all silages except in silage treated with B5, which had the poorest aerobic stability of all treatments. Treatments had no effect on DM recovery. Silages treated with PLB, PLB4, and LLB4 remained stable for >210 h.

Characterization and identification of Pediococcus species isolated from forage crops and their application for silage preparation

Pediococcus species isolated from forage crops were characterized, and their application to silage preparation was studied. Most isolates were distributed on forage crops at low frequency. These isolates could be divided into three (A, B, and C) groups by their sugar fermentation patterns. Strains LA 3, LA 35, and LS 5 are representative isolates from groups A, B, and C, respectively. Strains LA 3 and LA 35 had intragroup DNA homology values above 93.6%, showing that they belong to the species Pediococcus acidilactici. Strain LS 5 belonged to Pediococcus pentosaceus on the basis of DNA-DNA relatedness. All three of these strains and strain SL 1 (Lactobacillus casei, isolated from a commercial inoculant) were used as additives to alfalfa and Italian ryegrass silage preparation at two temperatures (25 and 48 degrees C). When stored at 25 degrees C, all of the inoculated silages were well preserved and exhibited significantly (P < 0.05) reduced fermentation losses compared to that of their control in alfalfa and Italian ryegrass silages. When stored at 48 degrees C, silages inoculated with strains LA 3 and LA 35 were also well preserved, with a significantly (P < 0.05) lower pH, butyric acid and ammonia-nitrogen content, gas production, and dry matter loss and significantly (P < 0.05) higher lactate content than the control, but silages inoculated with LS 5 and SL 1 were of poor quality. P. acidilactici LA 3 and LA 35 are considered suitable as potential silage inoculants.

Concentrations of Butyric Acid Bacteria Spores in Silage and Relationships with Aerobic Deterioration

Germination and growth of spores of butyric acid bacteria (BAB) may cause severe defects in semihard cheeses. Silage is the main source of BAB spores in cheese milk. The objectives of the study were to determine the significance of grass silages and corn silages as sources of BAB spores and to investigate the relationships between high concentrations of BAB spores in corn silage and aerobic deterioration. In the first survey, samples were taken from various locations in silos containing grass and corn silages and from mixed silages in the ration offered to the cows on 21 farms. We demonstrated that the quantity of BAB spores consumed by cows was determined by a small fraction of silage with a high concentration of spores (above 5 log10 BAB/g). High concentrations were most often found in corn silage within areas with visible molds (69% of the samples). Areas with visible molds in grass silage and surface layers of corn silage contained, respectively, 21 and 19% of the cases of concentrations above 5 log10 BAB spores/g. Based on these results, we concluded that currently in the Netherlands, corn silage is a more important source of BAB than is grass silage. In a second survey, 8 corn silages were divided into 16 sections and each section was studied in detail. High concentrations of BAB spores were found in only the top 50 cm of these 8 silages. Elevated concentrations of BAB spores were associated with different signs of aerobic deterioration. In 13% of the sections in corn silage with more than 5 log10 yeasts and molds/g, more than 5 log10 BAB spores/g were found. Sections with a temperature of more than 5 degrees C above ambient temperature contained, in 21% of the cases, more than 5 log10 BAB spores/g. Concentrations above 5 log10 BAB spores/g were measured in 50% of the sections with a pH above 4.4. All sections with a pH above 4.4 also showed a temperature that was more than 5 degrees C above ambient temperature and a concentration of yeasts and molds above 5 log10 cfu/g. Based on these results, we postulated that high concentrations of BAB spores in corn silage are the result of oxygen penetration into the silage, resulting in aerobic deterioration and the formation of anaerobic niches with an increased pH just below the surface. Growth of BAB in these anaerobic niches with an increased pH caused the locally high concentrations of BAB in corn silage.

Bacterial spores in silage and raw milk

Spore-forming bacteria can survive food-processing treatments. In the dairy industry, Bacillus and Clostridium species determine the shelf-life of a variety of heat-treated milk products, mainly if the level of post-process contamination is low. In order to minimize problems caused by bacterial spores in foods and food production processes a chain management approach, from raw materials, ingredients and environmental sources to final product storage conditions, is most effective. Silage is considered to be a significant source of contamination of raw milk with spores. PCR-RAPD fingerprinting and heat resistance studies of populations of aerobic spore-formers isolated from grass and maize silage and from raw milk confirmed this assumption. Prevention of outgrowth of aerobic spores in silage will contribute to reduction of the total spore load of raw milk. Therefore, it is important that the silage fermentation process is controlled. Application of cultures of lactic acid bacteria or chemical additives can aid silage fermentation and improve aerobic stability.

The effect of treating alfalfa with Lactobacillus buchneri 40788 on silage fermentation, aerobic stability, and nutritive value for lactating dairy cows

Lactobacillus buchneri 40788 and enzymes (beta-glucanase, alpha-amylase, xylanase, and galactomannase) were applied to chopped alfalfa (39% DM) to study their effects on the fermentation and nutritive value of the silage. Alfalfa was treated with nothing, or L. buchneri 40788, for a final application rate of 1 x 10(5), 5 x 10(5), or 1 x 10(6) cfu/g of fresh forage and ensiled in laboratory silos for 2, 4, 8, and 56 d. Treatment with L. buchneri 40788 had few effects on the end products of fermentation through 8 d of ensiling. However, after 56 d of ensiling, treated silages had a higher pH (4.55 vs. 4.38) and higher concentrations of acetic acid (6.40 vs. 4.24%), propionic acid (0.18 vs. 0.06%), and ammonia-N (0.35 vs. 0.29%) when compared to untreated silage. Lactic acid was also numerically lower in treated (3.51%) than untreated (4.12%). Silages treated with the moderate and highest dose of L. buchneri 40788 also resulted in greater recoveries of DM than did untreated silage. Alfalfa (43% DM) was also untreated or treated with a commercial application of L. buchneri 40788 (4 x 10(5) cfu/g, a commercial dose) in farm-scale bag silo. Holstein cows were fed a diet comprised of 32% untreated or treated alfalfa silage, 11% corn silage, 5% chopped alfalfa hay, and 52% of concentrate (DMB) for a 6-wk treatment period. Dry matter intake and milk composition were unaffected by treatment, but cows fed silage treated with L. buchneri 40788 produced 0.8 kg more milk than did cows fed untreated silage. Treated silage had a higher concentration of acetic acid (5.67 vs. 3.35%) but lower lactic acid (3.50 vs. 4.39%) than untreated silage. When exposed to air, the total mixed ration containing treated alfalfa silage remained stable for 100 h, whereas the ration containing untreated silage spoiled after 68 h. Treating alfalfa silage with L. buchneri 40788 increased the concentration of acetic acid, and when the silage was combined into a total mixed ration and fed to lactating cows, it improved the aerobic stability of the ration and increased milk production.

The effect of Lactobacillus buchneri, with or without homofermentative lactic acid bacteria, on the fermentation, aerobic stability and ruminal degradability of wheat, sorghum and maize silages

AIMS

To determine the effect of Lactobacillus buchneri, alone or in combination with homofermentative lactic acid bacteria (LAB), on the fermentation, aerobic stability and ruminal degradability of wheat, sorghum and maize silages.

METHODS AND RESULTS

The inoculants were applied at 1.0 x 10(6) CFU g(-1). Silages with no additives served as control. Three jars per treatment were sampled on days 2, 4, 8, 15 and 60 after ensiling, for chemical and microbiological analysis. At the end of the ensiling period, the silages were subjected to an aerobic stability test. The L. buchneri- and L. buchneri + L. plantarum-inoculated silages had significantly higher levels of acetic acid than the control and L. plantarum-inoculated silages (P<0.05). Therefore, yeast activity was impaired in the L. buchneri- and L. buchneri + L. plantarum-inoculated silages. As a result, L. buchneri, with or without L. plantarum, improved aerobic stability of the silages. The combination of L. buchneri and L. plantarum reduced pH, ammonia-N, and fermentation losses in the silages. However, L. buchneri, L. plantarum and L. buchneri + L. plantarum did not affect in situ dry matter, organic matters, and neutral detergent fibre degradability of the silages.

CONCLUSIONS

The L. buchneri was very effective in protecting the wheat, sorghum and maize silages exposed to air under laboratory conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The use of L. buchneri, with or without homofermentative LAB, as a silage inoculant can improve the aerobic stability of silages by inhibition of yeast activity.

Influence of ensiling temperature, simulated rainfall, and delayed sealing on fermentation characteristics and aerobic stability of corn silage

The aim of this study was to determine how delayed silo sealing, high ensiling temperatures, and rainfall at harvest affect the fermentation and aerobic stability of corn silage. One-half of each of 4 replicated, 6 x 1.5 m plots of a corn hybrid was harvested at 35% dry matter (Dry), and each of the other halves was harvested after they were sprinkled with sufficient water to simulate 4 mm of rainfall (Wet). Six representative (2 kg) subsamples were taken from the Wet and Dry forage piles and ensiled immediately (Prompt). Three hours later, 6 additional representative (2 kg) samples were taken from each pile and ensiled (Delay). Half of the bags from each moisture x sealing time treatment combination were stored for 82 d in a 40 degrees C incubator (Hot) and the other half were stored in a 20 degrees C air-conditioned room (Cool). A 2 (moisture treatments) x 2 (sealing times) x 2 (ensiling temperatures) factorial design with 3 replicates per treatment was used for the study. Wetting the corn silage increased concentrations of NH(3)-N, ethanol, and acetic acid. Ensiling at 40 instead of 20 degrees C increased pH, in vitro digestibility, and concentrations of NH(3)-N, residual water-soluble carbohydrates and acid detergent insoluble crude protein. The higher ensiling temperature also reduced concentrations of neutral and acid detergent fiber and lactic and acetic acid. Delayed sealing reduced concentrations of NH(3)-N and total volatile fatty acids. Wetting, high temperature ensiling, and delayed sealing each reduced yeast counts slightly, and marginally (8 h) increased aerobic stability. Hot-Wet-Delay silages were more stable than other silages but had the lowest lactic to acetic acid ratio, and total volatile fatty acid concentration. This study indicates that the fermentation of corn silage is adversely affected by wet conditions at harvest and high ensiling temperatures, whereas delayed silo sealing for 3 h caused no adverse effects.

Screening of fermentative bacteria for their ability to bind and biotransform deoxynivalenol, zearalenone and fumonisins in an in vitro simulated corn silage model

Fermentative bacteria can potentially be utilized to detoxify corn silage contaminated by Fusarium toxins. The objective of the present study was to test a large number of these bacteria for their ability to bind and/or biotransform deoxynivalenol (DON), zearalenone (ZEN) and fumonisins B(1) and B(2) (FB(1), FB(2)) in conditions simulating corn silage. A total of 202 strains were screened in contaminated, pH 4, corn infusion inoculated with 5 x 10(8) CFU ml(-1). Eight Lactobacilli and three Leuconostoc biotransformed ZEN into alpha-zearalenol, but no biotransformation was detected for DON and fumonisins. In contrast, most strains were capable of binding Fusarium toxins. The most effective genera were Streptococcus and Enterococcus, capable of binding up to 33, 49, 24 and 62% of DON, ZEN, FB(1) and FB(2), respectively. The ability to bind Fusarium toxins seems to be a common property of fermentative bacteria and could help to decrease their toxicity in animals.

Microbial populations, fermentation end-products, and aerobic stability of corn silage treated with ammonia or a propionic acid-based preservative

We studied the effects of ammonia treatment on microbial populations during the fermentation of corn silage. We also compared the effects of ammonia to a preservative containing buffered propionic acid and other antifungal compounds on the fermentation and aerobic stability of corn silage. In the first experiment, whole-plant corn was ensiled without treatment or treated with ammonia-N to supply an additional 0.3% N (fresh-forage basis). The addition of ammonia immediately increased silage pH and had no effect on numbers of lactic acid bacteria, but delayed their growth compared with untreated silage. Numbers of enterobacteria declined more slowly, but numbers of yeasts and molds declined more quickly in silage treated with ammonia. During the early stages of ensiling, lactic acid increased more rapidly in untreated than in treated silage. The reverse was true for acetic acid concentrations. When exposed to air, growth of yeasts and molds was delayed in ammonia-treated silage. In a second experiment, various levels (0.1 to 0.3%, fresh weight) of ammonium-N or a preservative with buffered propionic acid were added to whole-plant corn and allowed to ensile for 106 d. Silage treated with ammonia had a greater ratio of L- to D-lactic acid than did other silages. Untreated silage was aerobically stable for 32.3 h, whereas the low (42 h) and moderate (52.7 h) concentrations of both additives numerically improved aerobic stability. High concentrations of ammonia-N (0.3%) or a buffered propionic acid preservative (0.3%), markedly improved the aerobic stability of corn silage (82 and 69 h for ammonia and propionic acid-treated silage, respectively).

Mycotoxins and other secondary metabolites produced in vitro by Penicillium paneum Frisvad and Penicillium roqueforti Thom isolated from baled grass silage in Ireland

Secondary metabolites produced by Penicillium paneum and Penicillium roqueforti from baled grass silage were analyzed. A total of 157 isolates were investigated, comprising 78 P. paneum and 79 P. roqueforti isolates randomly selected from more than 900 colonies cultured from bales. The findings mostly agreed with the literature, although some metabolites were not consistently produced by either fungus. Roquefortine C, marcfortine A, and andrastin A were consistently produced, whereas PR toxin and patulin were not. Five silage samples were screened for fungal metabolites, with two visually moldy samples containing up to 20 mg/kg of roquefortine C, mycophenolic acid, and andrastin A along with minor quantities (0.1-5 mg/kg) of roquefortines A, B, and D, festuclavine, marcfortine A, and agroclavine. Three visually nonmoldy samples contained low amounts of mycophenolic acid and andrastin A. The ability of both molds to produce a diverse range of secondary metabolites in vitro and in silage should be a concern to livestock producers.

Cattle-to-cattle transmission of Mycobacterium bovis

This review, illustrated with data on the characteristics of herds infected with Mycobacterium bovis (TB) in Great Britain (GB), attempts to identify the role of cattle-to-cattle transmission (CCT) of TB. CCT plays a part in the entry of infection into herds, through purchased infected animals or contiguous spread, although CCT can have a relatively small role in comparison with an established wildlife source. Experimental studies have shown that it is possible for CCT to occur within herds. In 1999, more than one reactor was found in over two-thirds of confirmed TB incidents in Great Britain. The details of transmission from an infectious animal to a susceptible animal are described: proximate, which depends on factors such as closeness of contact and ventilation, or indirect, which also depends on survival outside the host. Herd size is a risk factor for the incidence of TB, both in herds and in individual cattle. Control of TB is considered in relation to the skin test: failure of the test to remove all infected animals from incidents is possible, but probably of less significance than failure to prevent reinfection from sources external to the herd. It is concluded that CCT may have significance in determining the total number of reactors. Safeguarding herds from other sources of TB is likely to reduce CCT as a side effect.