scholarly journals Influence of nitrogen source on the fermentation of fibre from barley straw and sugarbeet pulp by ruminal micro-organismsin vitro

2001 ◽  
Vol 86 (6) ◽  
pp. 717-724 ◽  
Author(s):  
M. J. Ranilla ◽  
M. D. Carro ◽  
S. López ◽  
C. J. Newbold ◽  
R. J. Wallace
Keyword(s):  
Volatile Fatty Acids ◽  
Statistical Significance ◽  
Growth Efficiency ◽  
Barley Straw ◽  
Daily Production ◽  
Total N ◽  
N Sources ◽  
N Source ◽  
Micro Organisms ◽  
Microbial N

Incubations were carried out with a batch culture system to study the effects of different N sources on the fermentation by ruminal micro-organisms from Merino sheep of two fibre substrates derived from feedstuffs that differed in their fermentation rate. The substrates were neutral-detergent fibre (NDF) from barley straw and sugarbeet pulp. N sources were ammonia (NH4Cl) and peptides (Trypticase). Three treatments were made by replacing ammonia-N with peptide-N at levels of 0 (AMMO), 33 (PEPLOW) and 66 % (PEPHIGH) of total N. There were no differences (P>0·05) between treatments in NDF degradation for both the barley straw and the sugarbeet pulp. Peptides increased (P<0·05) total volatile fatty acids daily production for both substrates, with greater values (P<0·001) for PEPHIGH than for PEPLOW for the sugarbeet pulp. The presence of peptides also increased (P<0·05) microbial N synthesis compared with AMMO, with PEPHIGH supporting more growth (P<0·001) than PEPLOW when the sugarbeet pulp NDF was fermented. The presence of peptides increased (P<0·01) the amount of solids-associated micro-organisms (SAM)-N for both the barley straw and the sugarbeet pulp fibres, values in the PEPHIGH treatment being higher (P<0·001) than those in PEPLOW. The proportion of SAM-N in the total microbial N was not affected (P>0·05) by the presence of peptides compared with the AMMO treatment, but values were greater for the PEPHIGH compared with the PEPLOW N source, reaching statistical significance (P<0·05) only for the sugarbeet pulp. For liquid-associated micro-organisms, the AMMO treatment resulted in the greatest (P<0·05) proportion of N derived from ammonia for both substrates, with a further decrease (P<0·01) for the PEPHIGH treatment compared with the PEPLOW for the sugarbeet pulp, indicating preferential uptake of peptides when they were available. Microbial growth efficiency (g microbial N/kg NDF degraded) was not affected (P>0·05) by N source. These results indicate that N forms other than ammonia are needed for maximal growth of fibre-digesting ruminal micro-organisms.

scholarly journals Influence of disodium malate on microbial growth and fermentation in rumen-simulation technique fermenters receiving medium- and high-concentrate diets

2005 ◽  
Vol 93 (4) ◽  
pp. 479-484 ◽  
Author(s):  
J. A. Gómez ◽  
M. L. Tejido ◽  
M. D. Carro
Keyword(s):  
Fatty Acids ◽  
Volatile Fatty Acids ◽  
Simulation Technique ◽  
Barley Straw ◽  
Feed Additive ◽  
Daily Production ◽  
Dairy Animals ◽  
Micro Organisms

Two incubation trials were carried out with the rumen-simulation technique (RUSITEC). In each trial, four vessels received a diet of grass hay and concentrate (600 and 400 g/kg DM, respectively; diet F), and the other four were fed a diet composed of concentrate and barley straw (900 and 100 g/kg DM, respectively; Diet C). Vessels were given 20 g of the corresponding diet daily, and half of them were supplemented with disodium malate to achieve a final concentration of 6.55 mM. There were no effects (P>0·05) of malate either on pH or on the daily production of NH3-N, but malate treatment increased (P<0·05) DM, neutral detergent and acid detergent fibre disappearance after 48 h incubation. The daily production of propionate and butyrate increased (P<0·001), and the ratio CH4:volatile fatty acids decreased (P<0·001) by supplementing both diets with malate. Whereas adding malate to the F diet produced an increase in acetate production (P=0·011) and the growth of solid-associated micro-organisms (P=0·037), no effects (P>0·05) were observed for diet C. For both diets, there were no differences (P>0·05) between treatments in the daily flow of liquid-associated micro-organisms measured using15N as a microbial marker. These results indicate that malate stimulated thein vitrofermentation of both diets by increasing the apparent disappearance of the diet and decreasing the ratio of CH4:volatile fatty acids, but a greater response was observed with diet F. If these results are confirmedin vivo, malate could be used as a feed additive for ruminants fed diets containing medium proportions of forage (i.e. dairy animals) and not only in animals fed high-concentrate diets, as has so far been proposed.

Estimation of microbial nitrogen in nylon-bag residues by feed15N dilution

1985 ◽  
Vol 54 (2) ◽  
pp. 473-481 ◽  
Author(s):  
T. Varvikko ◽  
J. E. Lindberg
Keyword(s):  
Sample Size ◽  
Incubation Time ◽  
Microbial Contamination ◽  
Barley Grain ◽  
Microbial Colonization ◽  
Diaminopimelic Acid ◽  
Barley Straw ◽  
Total N ◽  
Time Effects ◽  
Microbial N

1. Rapeseed (Brussicu nupus), barley grain, ryegrass (Loliurnperenne) and barley straw were labelled with15N as an internal marker. The dilution of15N was used to estimate microbial N (RMN15N) in the feed residues in nylon bags incubated in the rumen for 5, 12 and 24 h. For comparative purposes, diaminopimelic acid (DAP) content of the residues was also determined and rumen microbial N (RMNDAP-N) in the feed residues calculated using DAP as a bacterial marker. The influence of two bag pore sizes (20 μm and 40 μm) with different sample sizes (1 g and 5 g respectively) was also studied.2. For all feeds, the average disappearance of15N was faster than that of total N, the difference between N and15N disappearance being marked with barley, ryegrass and barley straw. The disappearance of microbially corrected dry matter (DM; correction calculated from the15N values) was, accordingly, always faster than the uncorrected DM disappearance. Except for the bag pore/sample size effect for N disappearance, significant (P < 0.01–0.001) feed, pore/sample size and incubation-time effects were always found for the disappearance values.3. Errors (%) resulting from the microbial contamination (calculated from the15N values) in N-loss measurement with rapeseed, barley, ryegrass and barley straw, at 5, 12 and 24 h in 20 μm bags were respectively: –1.8, –3.9, –0.9; –3.8, –22.4, –3.8; –7.2, –4.1, –2.9; –164.5, –146.3, –204.6. In 40 μm bags the corresponding errors were respectively: –4.4, –1.2, –0.7; –26.1, –10.5, –3.9; –13.2, –6.4, –5.5; –221.2, –310.1, –1284.6.4. The largest residual proportions of RMN15N, RMNDAP-Nand DAP-N (% of total N) were found in barley straw, followed by barley, ryegrass and rapeseed, in that order. RMN15N(g/kg residual DM) followed the descending order: barley, ryegrass, straw, rapeseed. RMNDAP-N, (g/kg residual DM) and DAP (mg/kg residual DM) followed the descending order: barley, ryegrass, rapeseed and barley straw. Feed, pore/sample size and incubation-time effects were always significant (P < 0.001).5. With 40 μm bags RMN15Nvalues of barley, ryegrass and barley straw (expressed as % of total N or g/kg residual DM) were substantially higher than those of RMNDAP-NWith 20 μm bags the RMN15Nand RMNDAP-Nvalues were generally quite close for these feeds. With rapeseed residues, RMN15Nwas clearly lower than RMNDAP-Nwith 20 μm bags, but only small differences were found with 40 μm bags.6. A more diverse microbial colonization of feed samples was indicated in the 40 μm bags compared with the 20 μm bags. It was also noticed, consequently, that in most cases larger error resulted from the microbial contamination in 40 μm bags.

scholarly journals Influence of peptides and amino acids on fermentation rate and de novo synthesis of amino acids by mixed micro-organisms from the sheep rumen

1999 ◽  
Vol 81 (4) ◽  
pp. 307-314 ◽  
Author(s):  
Cengiz Atasoglu ◽  
Carmen Valdés ◽  
C. James Newbold ◽  
R. John Wallace
Keyword(s):  
Amino Acids ◽  
Free Amino Acids ◽  
Free Amino ◽  
De Novo ◽  
Rumen Fluid ◽  
Amino Acid Synthesis ◽  
Fermentation Rate ◽  
N Sources ◽  
Micro Organisms ◽  
Microbial N

The influence of different N sources on fermentation rate and de novo amino acid synthesis by rumen micro-organisms was investigated in vitro using rumen fluid taken from four sheep receiving a mixed diet comprising (g/kg DM): grass hay 500, barley 299·5, molasses 100, fish meal 91, minerals and vitamins 9·5. Pancreatic casein hydrolysate (P; comprising mainly peptides with some free amino acids; 10 g/l), free amino acids (AA; casein acid hydrolysate + added cysteine and tryptophan; 10 g/l), or a mixture of L-proline, glycine, L-valine and L-threonine (M; 0·83 g/l each) were added to diluted (1:3, v/v), strained rumen fluid along with 15NH4Cl (A; 1·33 g/l) and 6·7 g/l of a mixture of starch, cellobiose and xylose (1:1:1, by weight). P and AA, but not M, stimulated net gas production after 4 and 8 h incubation (P < 0·05) in comparison with A alone. P increased microbial-protein synthesis (P < 0·05) compared with the other treatments. All of the microbial-N formed after 10 h was synthesized de novo from 15NH3 in treatment A, and the addition of pre-formed amino acids decreased the proportion to 0·37, 0·55, and 0·86 for P, AA, and M respectively. De novo synthesis of amino acids (0·29, 0·42 and 0·69 respectively) was lower than cell-N. Enrichment of alanine, glutamate and aspartate was slightly higher than that of other amino acids, while enrichment in proline was much lower, such that 0·83–0·95 of all proline incorporated into particulate matter was derived from pre-formed proline. Glycine, methionine, lysine, valine and threonine tended to be less enriched than other amino acids. The form in which the amino acids were supplied, as P or AA, had little influence on the pattern of de novo synthesis. When the concentration of peptides was decreased, the proportion of microbial-N formed from NH3 increased, so that at an initial concentration of 1 g peptides/l, similar to the highest reported ruminal peptide concentrations, 0·68 of cell-N was formed from NH3. Decreasing the NH3 concentration at 1·0 g peptides/l caused proportionate decreases in the fraction of cell-N derived from NH3, from 0·81 at 0·53 g NH3-N/l to 0·40 at 0·19 g NH3-N/l. It was concluded that different individual amino acids are synthesized de novo to different extents by mixed rumen micro-organisms when pre-formed amino acids are present, and that the source of N used for synthesis of cell-N and amino acids depends on the respective concentrations of the different N sources available; however, supplementing only with amino acids whose synthesis is lowest when pre-formed amino acids are present does not stimulate fermentation or microbial growth.

scholarly journals Effect of defaunation on the metabolism of rumen micro-organisms

1979 ◽  
Vol 42 (3) ◽  
pp. 515-524 ◽  
Author(s):  
D. I. Demeyer ◽  
C. J. Van Nevel
Keyword(s):  
Total Synthesis ◽  
Volatile Fatty Acids ◽  
Ammonium Bicarbonate ◽  
Energetic Efficiency ◽  
Specific Rate ◽  
N Incorporation ◽  
Micro Organisms ◽  
Acetate Butyrate ◽  
Microbial N

1. Rumen contents of a fasted fistulated wether, obtained in a faunated, defaunated and refaunated period were incubated in vitro with a mixture of cellobiose and maltose, in the presence of ammonium bicarbonate and32PO43−. Total synthesis of microbial N (Nt) was calculated from32P incorporation and N:P determined in microbial matter. The N:P value was not affected by defaunation. Net synthesis of microbial N (Nn) was calculated from ammonia-N incorporation. An estimate of degradation of microbial N was calculated as Nt–Nn. Energetic efficiency of synthesis was calculated from the volatile fatty acids produced during incubation, as g N incorporated per kg organic matter fermented (g N/kg OMf).2. Defaunation decreased the proportions of acetate, butyrate and methane and increased those of propionate in fermentation end-products. Fermentation rate when expressed per mg microbial N was not affected by defaunation.3. Expressed per unit volume of rumen contents, Nnwas increased by defaunation whereas Nfremained unchanged. Thus, a decrease in degradation can be calculated. Energetic efficiences of total and net synthesis were increased from 35 and 13 to 47 and 30 g N/kg OMfrespectively.4. Specific rates of both total and net synthesis of microbial N were significantly increased by defaunation whereas the specific rate of degradation was not affected.

scholarly journals Ammonia volatilization in no-till system in the south-central region of the State of Paraná, Brazil

2010 ◽  
Vol 34 (5) ◽  
pp. 1677-1684 ◽  
Author(s):  
Sandra Mara Vieira Fontoura ◽  
Cimélio Bayer
Keyword(s):  
Controlled Release ◽  
Central Region ◽  
Ammonia Volatilization ◽  
Nh3 Volatilization ◽  
The South ◽  
N Application ◽  
N Sources ◽  
South Central ◽  
N Source ◽  
No Till

Ammonia (NH3) volatilization can reduce the efficiency of urea applied to the surface of no-till (NT) soils. Thus, the objectives of this study were to evaluate the magnitude of NH3 losses from surface-applied urea and to determine if this loss justifies the urea incorporation in soil or its substitution for other N sources under the subtropical climatic conditions of South-Central region of Paraná State, Brazil. The experiment, performed over four harvesting seasons in a clayey Hapludox followed a randomized block design with four replicates. A single dose of N (150 kg ha-1) to V5 growth stage of corn cultivated under NT system was applied and seven treatments were evaluated, including surface-applied urea, ammonium sulfate, ammonium nitrate, urea with urease inhibitor, controlled-release N source, a liquid N source, incorporated urea, and a control treatment with no N application. Ammonia volatilization was evaluated for 20 days after N application using a semi-open static system. The average cumulative NH3 loss due to the superficial application of urea was low (12.5 % of the applied N) compared to the losses observed in warmer regions of Southeastern Brazil (greater than 50 %). The greatest NH3 losses were observed in dry years (up to 25.4 % of the applied N), and losses decreased exponentially as the amount of rainfall after N application increased. Incorporated urea and alternative N sources, with the exception of controlled-release N source, decreased NH3 volatilization in comparison with surface-applied urea. Urea incorporation is advantageous for the reduction of NH3 volatilization; however, other aspects as its low operating efficiency should be considered before this practice is adopted. In the South-Central region of Paraná, the low NH3 losses from the surface-applied urea in NT system due to wet springs and mild temperatures do not justify its replacement for other N sources.

Nitrogen excretion in germ-free and conventional chickens: effects of an alkali load

1978 ◽  
Vol 39 (1) ◽  
pp. 99-104 ◽  
Author(s):  
J. Okumura ◽  
D. Hewitt ◽  
Marie E. Coates
Keyword(s):  
Amino Acids ◽  
Uric Acid ◽  
Ammonia Excretion ◽  
Nitrogen Excretion ◽  
Acid Base Balance ◽  
Acid Base ◽  
Total N ◽  
Germ Free ◽  
Base Balance ◽  
Micro Organisms

1. Groups of three colostomized germ-free (GF) and conventional (CV) chickens aged 4 months were maintained for successive periods of 8 d on a diet containing 200 g casein/kg without and with sodium bicarbonate at the rate of 20 mmol/d and a nitrogen-free diet without and with NaHCO3at 9 mmol/d. Urine and faeces were collected during the last 3 d of each period.2. Total N, uric acid- and ammonia-N were determined in urine and total N in faeces. Amino acids were measured in hydrolysates of faeces collected during the periods when no NaHCO3was included in the diets.3. The CV birds excreted more N on the casein diets but less on the N-free diets than did their GF counterparts, the differences being mainly shown in the urine.4. On both diets hydrolysates of the faeces of CV birds contained smaller amounts of amino acids. On the N-free diet the proportions (g/160 g N) of serine, proline and threonine were reduced, suggesting some conservation of endogenous N by micro-organisms, and the proportions of histidine, alanine, lysine and methionine increased, possibly through microbial synthesis; on the casein diet, proportions of most amino acids were less, probably because bacterial deamination had occurred.5. Urinary excretion of total N, uric acid and ammonia was much greater on the casein than on the N-free diets. Inclusion of NaHCO3caused a sharp fall in urinary ammonia on both diets and in both environments.6. It was concluded that the level of dietary protein and the regulation of acid-base balance have more effect than microbial activity on the urinary ammonia excretion.

scholarly journals Effect of Dried Leaves of Leucaena leucocephala on Rumen Fermentation, Rumen Microbial Population, and Enteric Methane Production in Crossbred Heifers

Animals ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 300 ◽  
Author(s):  
María Denisse Montoya-Flores ◽  
Isabel Cristina Molina-Botero ◽  
Jacobo Arango ◽  
José Luis Romano-Muñoz ◽  
Francisco Javier Solorio-Sánchez ◽  
...  
Keyword(s):  
Organic Matter ◽  
Leucaena Leucocephala ◽  
Volatile Fatty Acids ◽  
Microbial Population ◽  
Nutrient Digestibility ◽  
Neutral Detergent Fiber ◽  
Daily Production ◽  
Enteric Methane ◽  
Four Levels ◽  
Fermentation Parameters

The effects of dietary inclusion of dried Leucaena leucocephala leaves (DLL) on nutrient digestibility, fermentation parameters, microbial rumen population, and production of enteric methane (CH4) in crossbred heifers were evaluated. Four heifers were used in a 4 × 4 Latin square design consisting of four periods and four levels of inclusion of DLL: 0%, 12%, 24%, and 36% of dry matter (DM) intake. Results showed that DM intake (DMI), organic matter intake, and gross energy intake (GEI) were similar (p > 0.05) among treatments. Apparent digestibility of organic matter, neutral detergent fiber, and energy decreased with increasing levels of DLL in the ration (p < 0.05). In contrast, digestible crude protein (CP) was higher (p < 0.05) in treatments with 12% and 24% DM of DLL. The inclusion of DLL did not affect (p > 0.05) rumen pH and total volatile fatty acids. Rumen microbial community was not affected (p > 0.05) by treatment. There was a linear reduction (p < 0.05) in CH4 emissions as the levels of DLL in the ration were increased. Results of this study suggest that an inclusion of 12% DM of ration as DLL enhances digestible CP and reduces daily production of enteric CH4 without adversely affecting DMI, rumen microbial population, and fermentation parameters.

scholarly journals Trade-Offs between Sugarcane Straw Removal and Soil Organic Matter in Brazil

2020 ◽  
Vol 12 (22) ◽  
pp. 9363
Author(s):  
Maristela C. Morais ◽  
Marcos Siqueira-Neto ◽  
Henrique P. Guerra ◽  
Lucas S. Satiro ◽  
Amin Soltangheisi ◽  
...  
Keyword(s):  
Organic Matter ◽  
Soil Health ◽  
Removal Rates ◽  
Total N ◽  
No Removal ◽  
Soil C ◽  
Sugarcane Straw ◽  
C Stock ◽  
Microbial C ◽  
Microbial N

Environmental benefits from bioenergy production derived from sugarcane crop residues (straw) can be lost by soil organic matter depletion resulting from excessive straw removal rates from fields. Soil organic carbon stock is the core for sustaining soil health, supporting nutrient cycling, and sequestering carbon dioxide. To find out that how much sugarcane straw can be removed from the field to produce bioenergy without changes in soil C concentrations, we investigated effects of straw removal rates (total, moderate, and no removal of sugarcane straw) on soil carbon and nitrogen fractions in an Oxisol and an Ultisol in southeastern Brazil for two years. Soil C and N fractions were affected by increased rates of straw removal at the second year. In the Oxisol, total straw removal decreased labile and microbial-C by ~30% and soil C stock by 20% compared to no straw removal. No removal decreased microbial-N and total N stock by ~15% and ~20%, respectively. In the Ultisol, no straw removal resulted in increases in C stock by >10% and labile and microbial-C by ~20% related to total straw removal. Total straw removal showed more microbial-N (~10%) and total-N stock (~25%) compared to no straw removal. The moderate straw removal intensity (i.e., 8 to 10 Mg ha−1 of straw) may control the straw-C release to soil by straw decomposition. This study suggests that excessive straw removal rates should be avoided, preventing SOM depletion and consequently, soil health degradation. Moderate straw removal seems to be a promising strategy, but long-term soil C monitoring is fundamental to design more sustainable straw management and bioenergy production systems.

Effect of stage of growth and silage additives on whole crop cereal silage nutritive and fermentation characteristics

2009 ◽  
Vol 49 (7) ◽  
pp. 595 ◽  
Author(s):  
J. L. Jacobs ◽  
J. Hill ◽  
T. Jenkin
Keyword(s):  
Lactic Acid ◽  
Volatile Fatty Acids ◽  
Limited Proteolysis ◽  
Triticum Aestivum L ◽  
Efficient Production ◽  
Total N ◽  
Boot Stage ◽  
Unit Costs ◽  
High Forage ◽  
Silage Additives

The efficient production and subsequent utilisation of home-grown forage is seen as the cornerstone of profitability of the dairy industry as it leads to lower unit costs of milk production compared with purchased forage or grain supplements. Cereals such as wheat (Triticum aestivum L.), oats (Avena sativa L.) and triticale (Triticum × Triticosecale) all have the potential to produce high forage dry matter (DM) yields. These forages are not widely grown within dryland Australian dairy systems and there is a paucity of information on both the agronomic requirements and subsequent ensiling and feed-out management under these conditions. The experiment reported in this paper examines the DM yield, nutritive and ensiling characteristics of three small-grain cereals (triticale, wheat and oats) cut at various stages of development and ensiled with or without silage additives. We hypothesised that: (1) delaying harvesting until later stages of growth would result in higher DM yields, but negatively impact on both nutritive and fermentation characteristics of subsequent silages; (2) ensiling wilted material at earlier harvests would improve fermentation characteristics compared with direct ensiled material; and (3) the use of silage additives at all harvests would improve fermentation characteristics of resultant silages compared with untreated silages. Apart from winter oats, the estimated metabolisable energy of forages was highest at the boot stage of growth, declined during anthesis and then rose again during milk and soft-dough stage of growth. The crude protein content of forages declined with maturity, with final values at soft dough below 90 g/kg DM. Neutral detergent fibre content was highest at anthesis and then declined, with lowest values observed at soft dough (497–555 g/kg DM). In the majority of cases silages were well preserved, with direct ensiled material having pH values generally below 4.5 and wilted material below 5.0, with limited proteolysis as assessed by ammonia-N contents in the range of 5–15% of total-N. The production of volatile fatty acids and lactic acid was influenced by wilting and the use of additives. Generally, wilted silages fermented less than the corresponding direct ensiled forages, whereas the use of Sil-All 4 × 4 additive resulted in a lactic acid-dominant fermentation compared with LaSil additive, which resulted in a greater proportion of acetic acid as an end product of fermentation. The findings of the present study highlight the potential of forage cereals to produce high DM yields for whole crop cereal silage. The timing of harvest directly influences nutritive characteristics of forages for ensiling. The use of silage additives can assist in controlling fermentation pathways during ensilage, ensuring the production of silages with fermentation attributes more likely to lead to higher intakes when fed to animals.

The effect of host diet on the cumulative gas production profile of grass hay and high temperature dried grass

1998 ◽  
Vol 22 ◽  
pp. 224-226
Author(s):  
J. A. Huntingtont ◽  
D. I. Givens
Keyword(s):  
High Temperature ◽  
Volatile Fatty Acids ◽  
Rumen Fluid ◽  
Gas Production ◽  
Barley Straw ◽  
Adaptation Period ◽  
Data Logger ◽  
Indirect Measure ◽  
Grass Hay ◽  
Host Diet

The gas production (GP) technique (e.g. Theodorou et al., 1994; Cone, 1994) is increasingly used as an indirect measure of substrate fermentability in the rumen. However, there are few data concerning the effect of making changes to the various integral steps of the GP procedure. This experiment was designed to study the effect of the host diet on the gas production profiles of grass hay and high temperature dried grass (HTDG).Two cows were given either a silage:barley diet (80:20 dry-matter (DM) basis) or barley straw (ad libitum). Four experimental periods with an adaptation period of 3 weeks were used so that each animal experienced each diet type twice. Rumen fluid and solids were collected at the end of each 3-week period, prepared and used to inoculate the cultures. Duplicate samples (milled, 1-mm screen) of either hay or HTDG were accurately weighed (̴ 0-5 g DM) into 250 ml bottles, 85 ml anaerobic buffer (as Theodorou et al., 1994) were then dispensed into each bottle before being connected to the automated GP data logger (as Cone, 1994). After 16 h bottles were inoculated with rumen fluid (15 ml) according to the experimental design and incubated at 39°C for 48 h. The GP data were fitted to the model suggested by France et al. (1993). A representative sample (8 ml) of final culture fluid was preserved with 1 mol/1 orthophosphoric acid (2 ml) and stored frozen (-20°C) to await analysis for volatile fatty acids.

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