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1.
A model of aerobic fungal growth in silage.   总被引：7，自引：0，他引：7  
The components of a simulation model of mesophilic and thermophilic yeast and mould growth in aerobically deteriorating silage are presented. The purpose of the model is to examine the relative roles of yeasts and moulds in deterioration and the factors affecting aerobic stability. Information for the model was based on literature studies. Growth of the fungi was assumed to be affected by temperature, pH, water activity, and lactic and acetic acid concentrations. The substrates utilized in the model, in order of preference, were water-soluble carbohydrates, ethanol, lactic acid and acetic acid. Gas movement and heat transfer were not considered. Consequently, oxygen and carbon dioxide concentrations were assumed to be those for open air, and the heat of respiration retained in the silage was set as a constant percentage of that released by fungal growth.
Based on the relationships developed for the model, pH affects yeast growth minimally and does not affect mould growth at all. Water activity over the range in silage affects yeast growth more than mould growth, but affects neither one strongly. Undissociated lactic and acetic acids decrease growth rate and may be important factors in silage stability. Compared with moulds, yeast growth rates are less affected by suboptimum temperatures but are more sensitive to temperatures in excess of the optimum.
A succeeding study compares the model with published aerobic deterioration studies and examines the predicted succession of microbial groups and the variation in silage stability as affected by silage parameters, initial temperature, and initial microbial populations.  相似文献   

2.
A mathematical model of the aerobic deterioration of silage is described that includes the physical processes of gas and heat Rows, as well as an established model of microbial growth and the associated chemical changes. Yeasts and acetic acid bacteria are included in the growth model. The version of the model described relates to a cylinder of silage subject to forced aeration, a common experimental configuration. The model was very sensitive to variations in insulation thickness and yeast growth rate, and to initial pH, especially when maize was the forage. Great care is needed when selecting input data for use in the model to be sure that the physical and chemical properties are accurate. The model solution was sensitive to grid size, but with 361 cells, the maximum grid resolution that could be used on a 486 series PC, solutions were achieved with an acceptably small loss of accuracy. The model predicted the results of an experiment on silage deterioration quite accurately. However, the model also predicted that considerable spatial gradients of parameters, such as temperature, pH, and lactic acid, would occur. This indicates the need for care when taking samples or making temperature measurements in deterioration experiments. The model is potentially a useful tool in predicting the optimal time and position to take samples for analysis in a time-course experiment.  相似文献   

3.
A simulation model of the growth and fermentation of lactic acid bacteria and clostridia in silage is described. The model is used to predict the occurrence of a well-preserved lactate silage or a poorly-preserved clostridial silage. Results of the model are compared with published experimental studies not used in the model's development. The results are summarized with maps showing the combinations of initial water-soluble-carbohydrate content, crop buffering capacity, dry matter content, temperature, initial pH, and initial population of lactic acid bacteria which result in a clostridial silage. The specific processes modelled include the growth and death of lactic acid bacteria and clostridia; the use of substrate and accumulation of fermentation end products; release of ammonia; and change in silage pH.  相似文献   

4.
A quantitative model of the ensilage process in lactate silages   总被引：2，自引：1，他引：1  
A model of the ensilage process is presented which can be used to predict silage quality in lactate silages. The model simulates the major microbial and biochemical processes during ensilage, including aerobic respiration, hydrolysis of hemicellulose. growth and death of lactic acid bacteria and their production of lactic and acetic acids, reduction in pH, change in soluble sugar content, increase in osmotic potential, and proteolysis. The model is designed to operate on mixtures of grasses, legumes, or whole-plant corn. Parameters for the model are developed from published silage experiments and pure-culture bacterial studies. The model gives reasonably accurate predictions of key silage quality parameters, but further experimental work is needed on growth of lactic acid bacteria and on plant-enzyme proteolysis. Predicted final pH depends primarily on the pH at which bacterial growth and death rates are equal. Initial bacterial concentration affects the time to rapid pH change, while maximum bacterial growth rate affects the rate of decline thereafter.  相似文献   

5.
Aerobic stability is an important feature in the evaluation of silages. The aims were to investigate the chemical and microbiological changes that occur in sugar-cane (Saccharum spp.) silage after aerobic exposure, to identify the major species of yeasts associated with the aerobic deterioration process and to select lactic acid bacteria (LAB) strains that can improve the aerobic stability of this silage. Fourteen wild LAB strains belonging to Lactobacillus plantarum, L. brevis and L. hilgardii were evaluated using experimental silos. Silage samples were collected at 0, 96 and 216 h after aerobic exposure to determinate the DM, WSC, pH, products of fermentation, to evaluate the silage temperatures and to identify yeast species associated with the aerobic deterioration of silage. The strains tested were able to modify the fermentative and chemical parameters and the diversity of yeasts species of silage after aerobic exposure. There was no association between the facultative or obligatory heterofermentative fermentation patterns and the increased aerobic stability of silage. Aerobic stability of sugar-cane silages was associated with high acetic acid and 1,2-propanediol concentrations. L. hilgardii UFLA SIL51 and UFLA SIL52 strains promoted an increase in aerobic stability of silage.  相似文献   

6.
Aerobic spoilage by yeasts and moulds is a major cause of reduced nutritional value of silage and increases the risk of potential pathogenic microorganisms. Recent studies have shown that inoculation with Lactobacillus buchneri inhibits yeast growth and reduces the susceptibility to aerobic spoilage of various ensiled forages. The aim of this study was to determine whether these effects are retained when L. buchneri is added in combination with homofermentative lactic acid bacteria. In three experiments, silages were produced from perennial ryegrass [240–421 g kg−1 dry matter (DM)] inoculated with L. buchneri or L. buchneri plus a mixture of Pediococcus pentosaceus and Lactobacillus plantarum (inoculant PL). Uninoculated silage and silage inoculated with PL alone served as controls. Silages were examined for pH and DM loss in the course of ensilage and chemical and microbiological composition and aerobic stability after 3–4 months. L. buchneri plus PL and PL alone increased the initial rate of pH decline. L. buchneri alone and L. buchneri plus PL enhanced aerobic stability and, in general, reduced yeast and mould counts. In addition, these inoculants increased the final pH and DM loss and the concentrations of acetic acid and 1,2-propanediol (or propionic acid and 1-propanol instead of 1,2-propanediol), and decreased the concentration of lactic acid. The effects of L. buchneri on fermentation products increased with decreasing DM content. In silages of less than 270 g kg−1 DM, L. buchneri increased the ammonia-N concentration. It is suggested that this was associated with the relatively high final pH resulting from the high metabolic activity of L. buchneri in these silages.  相似文献   

7.
为了改善木薯叶青贮品质,研究有机酸对木薯叶青贮品质及营养成分的影响,以确定青贮木薯叶最适合的有机酸种类及添加量。本研究以华南7号木薯幼嫩茎叶为原料进行青贮试验,设对照组、甲酸（0.2%）、乙酸（0.2%）和丙酸（0.2%）处理组,30 d后测定木薯叶青贮饲料pH、乳酸（LA）、乙酸（AA）、丙酸（PA）和丁酸（BA）含量以及主要营养成分含量。结果表明,木薯叶直接青贮品质较差,添加有机酸处理与对照相比显著降低青贮饲料的pH和丁酸含量（P<0.05）,降低中性洗涤纤维（NDF）和酸性洗涤纤维（ADF）含量（P<0.05）,提高了饲料相对值（RFV）。添加有机酸可以改善木薯叶青贮品质并提高营养价值,添加乙酸（0.2%）和丙酸（0.2%）青贮品质较好,可作为木薯叶青贮添加剂。  相似文献   

8.
This study was aimed to perform a screening of Lactobacillus buchneri strains from maize silage and use them as inoculant in maize and sugarcane silages. In all, 151 lactic acid bacteria (LAB) strains were isolated from whole‐plant maize silage, and their identification was based on the sequence analysis of 16S rDNA. In total, 15 strains were categorized to the L. buchneri group and eight of these were selected based on growth rate and fermentation pattern. The selected strains were evaluated on fermentation and aerobic stability of maize and sugarcane silages. For maize, the inoculated silages had lower pH and higher LAB population, but lower acetic acid concentration in comparison with the untreated control silage. For sugarcane silage, the strains 56.1, 56.4 and 40788 resulted in highest dry‐matter (DM) content and lowest DM losses. However, only the strain 40788 showed lowest counts of yeasts and moulds. Sugarcane silages inoculated with the strains 56.9, 56.26 and the untreated control silage showed highest concentrations of lactic acid and ethanol, besides the great DM losses. Even so, for both crops, the aerobic stability was not affected by inoculation. After air exposure, all silages increased temperature and had high population of yeast and moulds. Nevertheless, the strains 56.1 and 56.4 are promising for use as a silage inoculant.  相似文献   

9.
A mathematical model of the aerobic stability of grass silage is presented. The model is shown to predict as well as more complex models previously published. Sensitivity analysis performed on model parameters suggests that current understanding of the temperature dependence of yeast growth needs to be advanced in order to produce more accurate models of deterioration. Inhibition of yeast growth by organic acids is identified as a critical process worthy of further investigation. We discuss how model validation experiments must identify different yeast species and track their growth separately. Such experiments should also attempt to minimize or measure heat losses.  相似文献   

10.
Aerobically spoiled silage has often been shown to harbour dangerously high levels of Listeria monocytogenes. This paper investigates the dynamics of aerobic deterioration in a silage bale as it occurs close to a site of damage to the cover. The underlying aim was to enable prediction of the extent of the silage that may become suitable for Listeria growth during the course of storage. In order to meet these objectives, a model was formulated that represents the microbiology of the deterioration process and the transport of oxygen and heat through the silage. The geometry of the system was exploited to ensure that the model is computationally tractable. The model was used to evaluate the effect of silage pH and puncture size on the risk of Listeria contamination. Although the hazardous fraction was seen to be relatively insensitive to the initial pH of the silage, it increased rapidly with puncture size. However, a small puncture can result in the 'loss' of a considerable fraction of the bale because of the relatively long time scale over which bales are stored.  相似文献   

11.
本研究分析了龙眼干、枸杞和发芽糙米复合饮料采用酵母和醋杆菌进行连续发酵过程中其酒精度、pH、可滴 定酸、总糖、多糖、总酚和氨基酸态氮等品质指标的变化规律。结果表明,在酵母发酵期间,发酵 24 h 后复合饮料的 酒精度趋于稳定,残留的总糖为 1.40 g/L,多糖含量呈上升的趋势,总酚含量呈下降的趋势,氨基酸态氮总体上呈下降 的趋势。醋酸菌发酵期间,接种醋酸菌前热杀菌处理组和未热杀菌组的复合饮料中酒精度差别不大（p>0.05）,未热杀 菌处理组在发酵期间复合饮料中可滴定酸含量、总糖含量、多糖含量和氨基酸态氮的含量均比热杀菌组的复合饮料中 的含量高,但热杀菌组的复合饮料中总酚含量总体大于未热杀菌组的复合饮料中的总酚含量。  相似文献   

12.
A non-protein nitrogen additive containing ammonia, molasses and minerals was applied to precision-chopped forage maize to raise the crude protein content of the ensiled crop from approximately 8% to 10, 14 or 16%. The dry matter content, total nitrogen, water-insoluble nitrogen, and water-soluble nitrogen concentrations were measured at ensiling and 2 and 8 weeks later. The pH and lactic, acetic, propionic and butyric acid contents of the resultant silage were determined 2 and 8 weeks after ensiling. The levels of crude protein achieved were 10.8, 11.5 and 14.2%, which are equivalent to recoveries in the silages of 108, 82 and 89% of the applied nitrogen. After 8 weeks the water-insoluble nitrogen content of the treated silages had increased while the water-soluble nitrogen content had decreased. The increase in water-insoluble nitrogen may have been due to either decreased proteolysis or increased levels of microbial protein. There was a significant increase of 0.6 units in the pH of the silage when comparing the control to the highest rate of additive application. The additive increased the levels of lactic and acetic acid in the maize silage.  相似文献   

13.
A mixture of perennial and hybrid ryegrasses(234 g DM kg-1) was forage harvested and ensiled after a 24-h wilt in good ensiling conditions in 2-t capacity silos with no additive application (control) or with the application of either Lactobacillus plantarum , 4 × 106 (g fresh weight of grass)-1, or of 31 formic acid t-1. Sufficient 2-kg capacity laboratory silos were also filled with grass to monitor the changes in chemical composition of the ensiled grass with time. In laboratory silos, inoculation with L. plantarum resulted in a more rapid fall in silage pH ( p < 0.001) and a more rapid production of lactic acid ( P < 0.001) than in the control silage. At the end of the storage period (laboratory silos, 80 d; 2-t silos, 200-300 d), the inoculated silos had lower pH ( p ammonia-N (g kg N1) and acetic acid contents ( p < 0.01) and higher water soluble carbohydrate (WSC), lactic acid (P<00.1) and ethanol ( p < 0.05) contents than the control silage. The formic acid-treated silage had significantly lower contents of ammonia-N (g kg N-1, p < 0.05), acetic and tactic acids (p<0.01) and higher contents of WSC and ethanol ( p < 0.01) than the control silage. When fed to wether sheep, the digestibilities of DM, organic matter and gross energy were not altered by additive treatment. The digestibility of modified acid-detergent fibre was lower for both the inoculated ( P < 0.01) and formic acid-treated silages ( p < 0.05). However, N retention was improved ( p < 0.05) by both additive treatments. Silage intake was improved ( p < 0.01) by additive treatment from 53.4 (control) to 58.0 (inoculated) and 60.4 (formic acid) g DM (kg live weight0.75)-1d-1.  相似文献   

14.
This study attempted to separate the effects of forage source and field microbiota on silage fermentation quality and aerobic stability. Single samples of grass, red clover and maize were used. Field microbiota was obtained by centrifugation of microbial suspensions of the three samples. The intact forages were dried and sterilized by heating at 60°C for 3 h + 103°C for 15 h, inoculated in a 3 (forage) × 3 (inoculum) design and reconstituted to a dry‐matter level of 400 g kg?1 before ensiling. After ensiling for 71 d, subsamples were subjected to an 8‐d aerobic stability test, which included temperature and pH measurements. Bacterial community analysis was performed on samples before and after ensiling by 16S rRNA gene amplicon sequencing. Forage source had a marked effect on the levels of lactic acid, acetic acid, ammonia‐N and 2,3‐butanediol, but microbiota source only affected the acetic acid concentration. The forage and microbiota as well as their interactions affected silage stability variables. The maize microbiota improved silage stability, whereas silages made from the maize forage had the poorest stability. Bacterial community analysis revealed higher abundance of lactic acid bacteria on the maize forage, with Lactococcus and Leuconostoc being the dominant genera. These preliminary results suggested that fermentation quality is mainly affected by forage source, whereas the aerobic stability is affected by both forage and field microbiota.  相似文献   

15.
Use of big bale silage and haylage can be difficult on farms where daily forage consumption is comparatively low as speed of deterioration of forage after bale opening may be faster than feed-out rate. Production of smaller bales at harvest is possible, but expensive and work-intensive. Therefore, a pilot study of rebaling forage stored in big bales to smaller bales was conducted. Three separate experiments were included, where microbial and chemical composition of silage and haylage was studied before and after rebaling. In Experiment III, residual big bale forage stored and opened together with rebaled forage was included. Results showed that rebaled haylage and silage had higher yeast counts compared to initial forage; however, residual bales in Experiment III had yeast counts similar to rebaled forage, indicating an effect of storage time rather than of rebaling. In Experiment II, mould counts were higher in rebaled compared to initial silage, but not in haylage. Chemical composition was similar in initial and rebaled forage except for ammonia-N. In Experiment III, ammonia-N was higher in rebaled compared to initial and residual forage and was the only chemical variable affected by rebaling. Bale temperature during aerobic storage followed ambient temperature until day 6–8 in Experiment I and until day 14 in Experiment III where ambient temperature was lower. In conclusion, rebaling can be done without large changes in chemical composition of the forage, but yeast and mould counts may be higher in rebaled forage, and this risk should be considered when using this procedure.  相似文献   

16.
A model of the anaerobic phase of ensiling   总被引：1，自引：0，他引：1  
A model of ensiling is described which incorporates the interactions of lactic acid bacteria and Clostridia with water soluble carbohydrates. The processes modelled include bacterial growth, the production of lactic and butyric acids from water soluble carbohydrates, and the conversion of lactic acid to butyric acid. The calculation of pH, and the regulation of bacterial activity by pH are important components of the model. The model predicts time courses for pH and the five State variables, which are the concentrations of water soluble carbohydrates, lactic acid, butyric acid, lactic acid bacteria and Clostridia. There is good qualitative agreement between the predictions of the model and experimental data on ensiling.  相似文献   

17.
Field-wilted lucerne was chopped with a forage harvester at 33 ± 1·5, 43 ± 2·0 and 54 ± 1·8% dry matter, treated and ensiled in laboratory silos during four cuttings in each of two years. Treatments were control (C), sugar addition at 2% of fresh weight (S), inoculum applied at 3 × 105 bacteria g−1 herbage (I), and sugar and inoculum combined (IS). Duplicate silos were opened and analysed after 1, 2, 3, (4 or 5), 7, 14 and 60 d of fermentation. The initial rate of proteolysis of lucerne protein decreased with increasing dry matter (DM) content of the lucerne, and was not influenced by the year, cutting or silage treatment. Inoculation increased ( P <0·05) the rate of pH decline for all silage dry matters, and shortened the lag time prior to pH decline with 33 and 43% dry matter silages. Sugar addition had no effect on rate of pH decline or lag time. Inoculation and sugar addition both lowered final pH, acetic acid, ammonia (NH3), free amino acids (FAA) and soluble non-protein N (NPN) in silages ( P <0·01) and increased lactic acid content with 33 and 43% dry matter silages. Only inoculation was beneficial at 54% DM with no difference between I and IS. The influence of forage characteristics (epiphytic lactic acid bacteria, buffer capacity and sugar:buffer capacity ratio) on treatment effectiveness varied with dry matter content.  相似文献   

18.
Autumn-sown rye was cut on five dates in spring and ensiled in laboratory silos. On two of the dates forage-harvested material was ensiled in PVC silos (containing about 1 t of fresh crop) as well as in laboratory silos. Ensiling was carried out with and without the addition of formic acid or glucose solution. After 96 days in laboratory silos, rye cut before ear-emergence and ensiled without additives gave silages of high pH value and high ammonia content. After ear-emergence satisfactory silage was produced without an additive, but the addition of formic acid always resulted in silages having lower pH values and lower ammonia contents. The addition of glucose resulted in silages with only slightly lower pH values and ammonia contents which were closely similar to those made without addition. Silages made in PVC silos were all well preserved, as indicated by low contents of acetic and butyric acids, but the addition of formic acid resulted in pH values and ammonia contents lower than those found in other treatments.  相似文献   

19.
《Plant Production Science》2013,16(4):408-414
Abstract

To assess the potentiality of edible canna (Canna edulis Ker-Gawl.) as economically and environmentally sound animal feed, the feeding value of silage prepared from aboveground parts was examined, in parallel with studies on in situ digestion in the rumen among three local varieties. Contents of crude protein, acid and neutral detergent fibers and crude ash in canna silage were significantly higher, and that of nonstructural carbohydrate was significantly lower than in corn silage. The pH of corn and ‘yellow flower’ canna silages were significantly lower (3.8~3.9) than either ‘green stem’ or ‘red stem’ canna silage (4.4~4.9). The contents of lactic acid, acetic acid, total organic acid and the Flieg’s score of ‘yellow flower’ canna silage were equivalent or superior to those of corn silage. The rate of disappearance of dry matter in the rumen was significantly higher for corn silage than for canna silage, while the disappearance of neutral detergent fiber in canna silage was more rapid during the first 12 hours of incubation, but less rapid thereafter. The effective degradability of dry matter and organic matter of canna silage in the rumen was significantly higher than that of corn. Silage made from edible canna has a potential as a feed for ruminants.  相似文献   

20.
When silage is exposed to air on opening the silo, or after its removal from the silo, fermentation acids and other substrates are oxidized by aerobic bacteria, yeasts and moulds. The aerobic stability of silage is a key factor in ensuring that silage provides well‐preserved nutrients to the animal with minimal amounts of mould spores and toxins. In this paper, key findings and recent developments are reviewed, and findings of recent research are integrated in terms of four themes: (i) the most significant biochemical and microbiological factors, (ii) physical and management factors, (iii) type of additive and (iv) silo sealing. The development of yeasts and moulds during plant growth, and during field wilting or storage, and the concentration of undissociated acetic acid in silage are important microbiological and biochemical factors affecting aerobic stability. Silage density and porosity are key physical factors that affect the rate of ingress of oxygen into the silage mass during the feed‐out period. A target for potential silage aerobic stability is 7 d including time in the feed trough. To achieve this target, speed of harvest should be coordinated with packing tractor weight to achieve a minimum silage density by the time of feed‐out of 210 kg DM m?3, maximum proportional porosity of 0·4 and a rate of silage removal, which matches or exceeds the depth of air penetration into the silo. The use of additives to increase aerobic stability is advisable when there is the risk of these objectives not being met. Novel microbial approaches to solving the problem of silage aerobic deterioration are needed.  相似文献   

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