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PubMed1977

Pretreatment methods prior to gaschromatographic analysis of volatile fatty acids from faecal samples.

Vacuum distillation and steam distillation have been compared as pretreatment methods prior to the GC analysis of volatile fatty acids (VFA) in faecal material. Vacuum distillation resulted in a recovery range of 90-110% for all VFA in standard solutions. This was superior to the recovery ranges found after pretreatment by steam distillation. Coefficients of variance for steam distilled samples were higher than for vacuum distilled samples. Using a faecal homogenate, the vacuum distillation method was found to be highly reproducible. Spiking experiments substantiated the quantitative recovery of VFA from vacuum distilled samples. Modifications of the standard vacuum distillation procedure showed that care must be taken to ensure adequate cooling of the receiver tube.

Analysis of Variance↗

PubMed1988

Production of volatile fatty acids as a result of bacterial interactions in the cecum of gnotobiotic rats and chickens fed a lactose-containing diet.

Volatile fatty acid (VFA) productions from lactose and lactate by a Clostridium butyricum and a Veillonella alcalescens strain, alone or in combination with a Lactobacillus acidophilus strain, were determined both in vitro in culture media and in vivo in the ceca of gnotobiotic animals. Gnotobiotic rats, which possess intestinal lactase, and chickens, which are devoid of it, were used. Both animal species were fed a diet containing 4% lactose. The in vitro results showed that the C. butyricum strain fermented lactose and D-lactic acid to butyric and acetic acids, whereas L-lactic acid was not fermented. The V. alcalescens strain did not ferment lactose and fermented L better than D-lactic acid. The in vivo results showed that high VFA concentrations were obtained in the ceca of chickens either disassociated with V. alcalescens or C. butyricum and Lactobacillus strains or monoassociated with C. butyricum. VFA concentrations in the ceca of rats were low, whatever strain the rats harbored. In addition, an antagonistic effect of the C. butyricum strain against the Lactobacillus strain was evidenced both in rats and chickens. It is suggested that the absence of a host lactase makes the chick a good model for lactose intolerance studies in human newborns.

Anaerobiosis↗

PubMed1994

Volatile fatty acid concentrations, enzyme activities and microflora in the rumen contents of heifers during transition to pasture.

Observations were carried out on volatile fatty acid (VFA) concentrations, enzyme activities and the microflora of the rumen contents in heifers during transition from winter to pasture feeding and in the subsequent gazing cycles. After turn-out to pasture, total VFA concentrations in the rumen contents of heifers significantly decreased from 107.7 to 88.7 mmol.l-1 (P < 0.01). After subsequent increase the total VFA concentrations reached their highest value (117.0 mmol.l-1) in the 8th week of grazing. The proportion of the molar acetic acid concentration in the rumen content increased insignificantly whereas that of propionic acid decreased insignificantly. In the molar proportion of butyric acid no significant differences could be stated. In the subsequent weeks the molar proportions of acetic acid were rather balanced and ranged within 66.2 and 68.0 mol%; the molar proportion of propionic acid insignificantly increased in the 4th week (18.7 mol%). Molar proportions of butyric acid on pasture insignificantly increased in week 3 (15.2 mol%) and appeared as balanced, later acquiring values between 14.0 and 14.8 mol%. The energetic yield of VFA production in the rumen of heifers decreased insignificantly from 73.6 to 72.15; the acetate: propionate ratio revealed an insignificant increase from 3.66 to 4.18. The enzyme activity of cellulase (endoglucanase E.C.3.2.1.4 and cellobiohydrolase E.C.3.2.1.91.) decreased significantly from 17.83 to 16.64 micrograms.ml-1 (P < 0.01); in the subsequent weeks, however, a significant increase could be observed. The enzyme activity of alpha-amylase (E.C.3.2.1.1.) decreased significantly (P < 0.05). In the 4th week a significant increase of the former occurred. The numbers of cellulolytic bacteria in the rumen content decreased significantly from 8.08 to 7.61 log 10.ml-1 (P < 0.01) and then a significant increase to 8.39 log 10.ml-1 was observed again in the 3rd week of grazing (P < 0.05). During pasture, a significant increase of the numbers of lactate-utilizing bacteria was recorded. As to the numbers of lactobacilli a significant decrease (P < 0.05) with a subsequent insignificant increase during grazing could be observed. Throughout the grazing season, the numbers of Streptococci reached values that surpassed those recorded during the winter feeding period. After transition from winter feeding to pasture the adaptation of rumen fermentation took four weeks.

Animal Feed↗

PubMed1992

Vertebrate gastrointestinal fermentation: transport mechanisms for volatile fatty acids.

Symbiotic microbial fermentation of plant polysaccharides can potentially provide significant levels of nutrients to host organisms in the form of volatile fatty acids (VFAs). Microbial fermentation can account for as much as 10% of maintenance energy requirements in carnivores and omnivores, and up to 80% in ruminant herbivores. In this review epithelial transport processes for the products of microbial fermentation are described in various mammalian and lower vertebrate species. Studies of transepithelial movement of VFA in vertebrate gastrointestinal systems have mostly been investigated in the mammals. In these it is widely held that the transmural movement of VFA is a concentration-dependent passive diffusion process whereby VFA is transported in the protonated form. A different model is described in this paper for carrier-mediated VFA transport, by way of anionic exchange with intracellular bicarbonate, in the intestine of a fermenting herbivorous teleost. These models for diffusive and carrier-mediated transport are compared and discussed from both physiological and experimental viewpoints.

Animals↗

PubMed1990

[Effects of infusions of a complete mixture of volatile fatty acids during a meal on the food intake of dry or lactating cows].

Infusions of 3 or 6 mol of a volatile fatty acid mixture into the rumen for 3 h during the morning feeding depress feed intake of lactating dairy cows (1.5 kg of dry matter (DM)) and, to a lesser extent, that of dry cows (0.8 kg DM). These differences occur between 1 and 3 h after the beginning of the meal and are not recovered over the day.

Animals↗

PubMed1975

[Effect of potato starch on the level of volatile fatty acids and ammonia in sheep's rumen].

Two experiments were performed on adult sheep, which were given intraruminally potato starch in a single dose of 1500 g and in gradually increasing doses. The effect of starch on the level of volatile fatty acids, ammonia and the pH value was studied. In the rumen content, the level of pH slightly decreased and that of volatile fatty acids increased. Ammonia level decreased after starch administration. No lactic acid was found in the rumen content.

Ammonia↗

PubMed2003

Dynamics of the anaerobic process: effects of volatile fatty acids.

A complex and fast dynamic response of the anaerobic biogas system was observed when the system was subjected to pulses of volatile fatty acids (VFAs). It was shown that a pulse of specific VFAs into a well-functioning continuous stirred tank reactor (CSTR) system operating on cow manure affected both CH(4) yield, pH, and gas production and that a unique reaction pattern was seen for the higher VFAs as a result of these pulses. In this study, two thermophilic laboratory reactors were equipped with a novel VFA-sensor for monitoring specific VFAs online. Pulses of VFAs were shown to have a positive effect on process yield and the levels of all VFA were shown to stabilize at a lower level after the biomass had been subjected to several pulses. The response to pulses of propionate or acetate was different from the response to butyrate, iso-butyrate, valerate, or iso-valerate. High concentrations of propionate affected the degradation of all VFAs, while a pulse of acetate affected primarily the degradation of iso-valerate or 2-methylbutyrate. Pulses of n-butyrate, iso-butyrate, and iso-valerate yielded only acetate, while degradation of n-valerate gave both propionate and acetate. Product sensitivity or inhibition was shown for the degradation of all VFAs tested. Based on the results, it was concluded that measurements of all specific VFAs are important for control purposes and increase and decrease in a specific VFA should always be evaluated in close relationship to the conversion of other VFAs and the history of the reactor process. It should be pointed out that the observed dynamics of VFA responses were based on hourly measurements, meaning that the response duration was much lower than the hydraulic retention time, which exceeds several days in anaerobic CSTR systems.

Acetates↗

PubMed1991

Avian cecum: role of glucose and volatile fatty acids in transepithelial ion transport.

In the fowl cecum in vitro, the influence of glucose and the three most prevalent naturally occurring volatile fatty acids (acetate, propionate, butyrate) on short-circuit current (Isc), electrical resistance, and transport of Na and Cl was determined. When glucose, acetate, or butyrate was present, ion transport was characterized by electrogenic Na absorption, greater than 65% of which was amiloride inhibitable, and Cl secretion, which also was electrogenic. Isc could be completely accounted for by net fluxes of Na and Cl. When glucose, acetate, or butyrate (10 mM both sides) was included in the incubation medium, cecal tissue maintained its Isc and a constant rate of net Na absorption and Cl secretion for a 5-h period. When no substrate was present or propionate was included in the medium, a marked fall in Isc and net Na and Cl fluxes was seen. Glucose caused an increase in Isc when added only to the serosal side. As 3-O-methylglucose (not metabolized) was not effective in stimulating Isc of the cecum (serosal or mucosal addition), it appeared that glucose increased Isc by acting as an energy substrate for active Na transport. Acetate and butyrate appeared to be equally effective in stimulating Na transport and Isc when placed on either side of the membrane. When the preparation was supplied with glucose (serosal side) and acetate was added to the mucosal side, no further stimulation of Isc occurred. Thus it appeared that acetate and butyrate were acting as substrates for active Na transport rather than stimulating Na transport by some other mechanism such as a cotransport with Na.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetates↗

PubMed1982

Rumen volatile fatty acid production and nutrient utilization in steers fed a diet supplemented with sodium bicarbonate and monensin.

Effects of feeding dietary supplements of monensin and sodium bicarbonate singly or in combination on production of rumen volatile fatty acids, nitrogen balance, and rumen water kinetics were studied. Four rumen fistulated steers were fed a diet (50% concentrate mix and 50% corn silage) ad libitum in a 4 X 4 Latin square design (21-day periods) with a 2 X 2 factorial arrangement of treatments. Sodium bicarbonate increased feed intake, water intake, rumen pH, fluid dilution rate, and decreased both molar proportion and production rate of propionate in the rumen. Alteration of the ratio of acetate to propionate reflects the large decrease in propionate production relative to the small increase in acetate production. In contrast, monensin did not alter significantly rumen fluid dilution rate or ruminal pH but did decrease the molar proportion of acetate and increase that of propionate. Monensin increased production of both acetate and propionate in the rumen; however, the large increase in propionate production appears to account for more of the increase in molar proportion of propionate in the rumen. Increases in total volatile fatty acid production per kilogram of dry matter consumed with monensin supplementation appears to result from decrease in feed intake, thereby increasing ruminal retention time of dry matter and potentially the extent of digestion. Efficiency of nitrogen utilization was not altered by either sodium bicarbonate or monensin.

Animals↗

PubMed1965

Interconversions and production of volatile fatty acids in the sheep rumen.

1. Sheep fed at a constant rate were infused intraruminally with [1-(14)C]-acetate, -propionate or -butyrate during 5hr. periods. 2. Volatile fatty acids were estimated in the rumen contents and steady-state conditions were obtained. 3. Of the butyric acid carbon 60% was in equilibrium with 20% of the acetic acid carbon, and 2-3g.atoms of carbon were interconverted/day. 4. Little interconversion took place between propionic acid, acetic acid or butyric acid. 5. The net production rates for acetic acid, propionic acid and butyric acid were 3.7, 1.0 and 0.7moles/day respectively. 6. The production of volatile fatty acids accounted for 80% of the animal's energy expenditure.

Journal Article↗

PubMed2005

Effect of oral nitroethane and 2-nitropropanol administration on methane-producing activity and volatile fatty acid production in the ovine rumen.

Strategies are sought to reduce economic and environmental costs associated with ruminant methane emissions. The effect of oral nitroethane or 2-nitropropanol administration on ruminal methane-producing activity and volatile fatty acid production was evaluated in mature ewes. Daily administration of 24 and 72 mg nitroethane/kg body weight reduced (P<0.05) methane-producing activity by as much as 45% and 69% respectively, when compared to control animals given no nitroethane. A daily dose of 120 mg 2-nitropropanol/kg body weight was needed to reduce (P<0.05) methane-producing activity by 37% from that of untreated control animals. Reductions in methane-producing activity may have been diminished by the last day (day 5) of treatment, presumably due to ruminal adaptation. Oral administration of nitroethane or 2-nitropropanol had little or no effect on accumulations or molar proportions of volatile fatty acids in ruminal contents collected from the sheep. These results demonstrate that nitroethane was superior to 2-nitropropanol as a methane inhibitor and that both nitrocompounds reduced ruminal methanogenesis in vivo without redirecting the flow of reductant generated during fermentation to propionate and butyrate.

Administration, Oral↗

PubMed1994

Osmotic pressure, water kinetics and volatile fatty acid absorption in the rumen of sheep sustained by intragastric infusions.

The effects of changing rumen osmotic pressure (OP) upon water kinetics and volatile fatty acid (VFA) absorption in the rumen of sheep were studied in two 4 x 4 Latin square experiments, each using four lambs with a rumen cannula and an abomasal catheter. In both experiments the lambs were sustained by the intragastric infusion of all nutrients (VFA, Ca, P, Mg and a buffer solution into the rumen, and casein, vitamins and trace elements into the abomasum). On experimental days, which were at least 1 week apart, drinking water and the casein infusion were withdrawn, and the ruminal OP was changed and held constant for 9.5 h, by incorporating NaCl at different concentrations in the buffer solution being infused. In Expt 1 the target OP values were 300, 340, 380 and 420 mosmol/kg, and in Expt 2 were 261 (no saline addition), 350, 420 and 490 mosmol/kg. Using soluble non-absorbable markers (PEG in continuous infusion and Cr-EDTA injected in pulse doses) rumen volume, liquid outflow rates, apparent water absorption through the rumen wall and VFA absorption rates were estimated at six sampling times corresponding to the 1.5 h intervals during the last 7.5 h following the change in rumen OP. Liquid outflow rate (F; ml/h) showed a significant and positive linear relationship with the rumen OP (mosmol/kg), resulting in the equation F = 1.24 OP (SE 0.096)-36.5 (SE 36.6) (r2 0.96). Similarly, water absorption rate (W; ml/h) was significantly affected by rumen OP, and this relationship was given by W = 395 (SE 39.9)-1.16 OP (SE 0.105) (r2 0.95), which means that for an OP of 341 mosmol/kg the net movement of water across the rumen wall would be zero, and either a net efflux or a net influx of water would be observed with lower or higher OP respectively. In Expt 2 there was a significant linear effect of OP on rumen volume (P < 0.01), with higher OP being associated with increases in rumen liquid contents of about 10-20%. As rumen OP was increased there was also a decline in the absorption rate of VFA (from 232 mmol VFA/h for OP 350 to 191 mmol/h for OP 490 mosmol/kg), resulting in the accumulation of VFA (especially acetate) in the rumen and a consequent fall in rumen pH. Rumen OP seems to be important in defining water movement across the rumen wall and, hence, partitioning between absorption and outflow.

Animals↗

PubMed2001

Comparison of non-tracer and tracer methods for determination of volatile fatty acid production rate in the rumen of sheep fed on two levels of intake.

The aim of the present work was to estimate volatile fatty acid (VFA) production rate in the rumen of sheep fed two levels of intake using both a tracer (TM; by isotope dilution) and a non-tracer method (NTM; by supplementary infusion) in steady-state conditions. Six wethers received a diet containing 700 g lucerne hay and 300 g ground maize/kg in eight equal meals at 3 h intervals per d. The diet (9.8 MJ metabolizable energy (ME)/kg DM) was offered at 90 % ad libitum consumption (high intake, HI) or 45 % ad libitum consumption (low intake, LI) in a crossover design. Each sheep received five intrarumen VFA solutions infused continuously for 24 h at rates of 250 ml and 165 ml/h for the HI and LI respectively. The first infusion, considered as a control treatment (Con), consisted of a solution of [1-(13)C]propionate (7 mmol/d). The four other solutions were isoenergetic (1.9 MJ ME/kg DM intake) mixtures of unlabelled propionate (C(3)) and butyrate (C(4)) at different levels: 0.90 mol C(4)/kg DM intake; 0.60 mol C(3)/kg DM intake; 0.30 mol C(3)/kg DM intake; 1.35 mol C(3)/kg DM intake. The VFA infusions did not affect rumen fermentation of the basal diet (pH, osmotic pressure, protozoa numbers), and comparable DM digestibility of the diet among the different treatments was observed. Both estimation methods demonstrated a similar increase (1.7-fold) in the rumen VFA production rate of sheep fed at intakes varying between 0.9 to 1.7 times maintenance. Irrespective of the intake level, the rumen production rate of individual VFA was on average 1.5-fold higher when estimated by the TM compared with the NTM. Rumen VFA production rates estimated by the NTM and TM represented 80 % and 120 % ME intake respectively. The difference between NTM and TM estimates seems likely to be caused mainly by overestimation of the VFA production rates by the TM.

Analysis of Variance↗

PubMed1999

Effects of a xylanase on individual bird variation, starch digestion throughout the intestine, and ileal and caecal volatile fatty acid production in chickens fed wheat.

1. The effects of a xylanase on digesta viscosity and starch digestibility throughout the small intestine and volatile fatty acid production in the ileum and caeca were investigated in broilers fed on a low-metabolisable energy wheat diet. 2. The xylanase reduced (P<0.01) duodenal (2.9 vs. 1.7), jejunal (4.6 vs. 2.3) and ileal (14.0 vs. 3.9) digesta viscosities (mPas) and increased AME (P<0.01) of the wheat and starch digestibility (P<0.5) in the jejunum and ileum. Between-bird variability in ME and digestibility of starch was also reduced. 3. Enzyme supplementation reduced (P<0.05) fermentation in the ileum, but increased (P<0.05) it in the caeca. 4. The anti-nutritive effect of soluble non-starch polysaccharides (NSP) is related to their ability to increase digesta viscosity along the gut; this in turn causes changes in gut microflora and efficiency of nutrient utilisation by the chicken. Use of appropriate enzymes is an effective way of dealing with grains with high NSP content in poultry diets.

Animal Feed↗

PubMed1989

Preparation of fecal samples for assay of volatile fatty acids by gas-liquid chromatography and high-performance liquid chromatography.

We describe a procedure for preparing fecal samples for determination of volatile fatty acids (VFAs) by gas-liquid chromatography (GLC) and "high-performance" liquid chromatography (HPLC). The simple, one-step procedure involves only ultrafiltration through a membrane with a molecular-mass cutoff of 3000 Da. As revealed by the GLC chromatograms, ultrafiltration appears to be as effective as steam distillation in sample clean-up. It also enables higher, more reproducible analytical recoveries of long-chain VFAs. The VFA content of the filtrate can also be measured by HPLC. Use of the ion-exclusion mechanism completely resolves isobutyric acid and butyric acid on a cation-exchange column. The mean (+/- SD) percentage distribution values of VFAs (measured by GLC) from five healthy subjects were 56.0 +/- 3.5 (acetic acid), 17.0 +/- 5.3 (propionic acid), 2.9 +/- 1.5 (isobutyric acid), 18.8 +/- 5.8 (butyric acid), 2.3 +/- 1.2 (isovaleric acid), and 2.9 +/- 0.8 (valeric acid).

Acetates↗

PubMed1982

Diagnosis of anaerobic infection by gas chromatographic estimation of volatile fatty acids.

Nine hundred and eighty-one fluid specimens were analysed by culture and by gas chromatography. The presence of obligate anaerobes was best predicted if one or more of the volatile acids isobutyric, butyric, isovaleric, valeric, isocaproic or caproic acid were detected in the specimen. Propionic acid was not a good indicator of the presence of obligate anaerobes. The agreement between gas chromatography and culture for obligate anaerobes in the main study (841 specimens, 232 culture positive) was: co-positivity 82%; co-negativity 92%. Falsely negative specimens contained anaerobes which had probably not produced sufficient of their characteristic volatile fatty acids to be detected. When it was the sole infecting anaerobe, Bacteroides fragilis seemed especially likely to be missed by gas chromatography. Forty-five of the 51 falsely positive specimens probably represented failure to culture anaerobes rather than spurious volatile fatty acid detection.

Anaerobiosis↗

PubMed1976

Determination of volatile fatty acids C1--C6, and lactic acid in silage juice.

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Animal Feed↗

PubMed1994

The Ca-activated chloride channel of Ascaris suum conducts volatile fatty acids produced by anaerobic respiration: a patch-clamp study.

Plasma membrane vesicles prepared from the bag region of the somatic muscle cell of the parasite Ascaris suum contain a large conductance, voltage-sensitive, calcium-activated chloride channel. The ability of this channel to conduct a variety of carboxylic acids, a number of which are products of anaerobic respiration, was investigated using the patch-clamp technique and isolated inside-out patches of muscle membrane. The channel has a conductance of 140 pS in symmetrical 140 mM chloride. Replacement of internal chloride with various carboxylic acids (140 mM) caused large hyperpolarizing shifts in the reversal potential. Permeability ratios, relative to chloride, were calculated for each acid. The relationship between permeability ratio and ionic size is inverse and linear predicting a pore diameter of 6.55 A. This simple relationship was not observed between ionic size and conductance. Calculation of the transition state energy required to transfer a single methyl group from aqueous phase to the binding site afforded a value that was low but favorable, indicating a cationic binding site of low field strength. As the channel is able to open fully at the resting membrane potential of Ascaris and is permeable to fatty acids produced by anaerobic respiration, the possible role of this channel in the removal of metabolic products across the muscle membrane is discussed.

Animals↗