In vitro simulation of rabbit cecal fermentation in a semi- continuous flow fermentor. I. Role of food substrate pretreatment]

A Rusitec semi-continuous flow fermentor was used to study the influence of enzyme pretreatment of food substrates on the fermentation profile over a 2-week period following inoculation with rabbit caecal contents. Three types of substrate were examined: 1) homogenized commercial rabbit feed; 2) the solid remains of this feed after digestion with alpha-amylase for 24 h; and 3) substrate 2 digested for 4 h with pepsin (double enzyme treatment). One of a pair of nylon pouches containing 15 g substrate was replaced each day, thus producing a uniform 48-h fermentation. Fermentation of the untreated feed (1) for 5-6 days produced a fermentation profile quite different from that obtained in vivo in the rabbit caecum: propionic acid accounted for over 35% of total volatile fatty acid (VFA), and butyric acid for about 15%. Amylase digestion (2) gave a stable ferment profile closer to the in vivo profile, except that propionic and butyric acids were similar at 15% of total VFA. Digestion with both amylase and pepsin (3) produced a stable fermentation profile very close to the in vivo profile: C2 > 60%, C3 < 11% and 17% < C4 < 21%. The rate at which membrane constituents (acid detergent fibre, ADF) were lost in 48 h was similar to the digestibility coefficient measured in vivo by others for the same basic feed. Lastly, there was a high percentage (about 5%) of volatile C5 fatty acids; this could be due to the discontinuous fermentor input of one pouch per 24 h. Thus, feed pretreated with both amylase and pepsin simulates, in vitro, rabbit caecal fermentation in a semi-continuous Rusitec type fermentor.     

Fermentation of carbohydrates and yield of microbial protein in mixed cultures of rabbitcaecal microorganisms

Fermentation pattern and yields of microbial protein were investigated in cultures of the rabbit caecal contents supplied with glucose, xylose, starch, pectin and xylan. Rabbits at the age of 4 weeks (before weaning) and 3 months were slaughtered, their caecal contents added at 1.1% to growth media and incubated anaerobically at 39°C for 18 h. Caecal microorganisms of 4‐week‐old rabbits produced no methane and caproate, less butyrate, but more propionate than microorganisms of 3‐month‐old rabbits. In both groups of rabbits, fermentation of xylose produced significantly more propionate and less butyrate than fermentation of glucose. More propionate and less acetate was formed from starch than from pectin. In caecal cultures from 4‐week‐old rabbits with pectin, the molar percentages of acetate was significantly higher and percentages of other short‐chain fatty acids (SCFA) lower than in cultures with starch or xylan. In cultures from 3‐month‐old rabbits, fermentation of pectin and xylan produced similar SCFA profiles, different from SCFA molar composition in cultures with starch. Average production of microbial protein was 129mg per lg of carbohydrate digested (range 110 to 141mg/g). Protein yields were the same on glucose and xylose, but nonsignificantly higher on starch than on pectin and xylan. It can be concluded that the characteristics of substrate affected fermentation pattern in mixed cultures of rabbit caecal microorganisms. Substrate effects on protein yields were not statistically significant, due to high variation.     

Influence of storage time and temperature on in vitro digestion of neutral detergent fibre at 48 h, and comparison to 48 h in sacco neutral detergent fibre digestion

The effect of within-day delays of 0.5, 2.5, 4.5 and 6.5 h between collection of rumen fluid from a cow and initiation of in vitro fermentation, as well as storage of rumen fluid for 48 h at either −24°C or 6, 22 and 39°C, on in vitro digestion of neutral detergent fibre (NDF) at 48 h was determined. In addition, the 48 h in vitro digestion of NDF, determined with a minimum time delay (i.e., 0.5 h) between collection from the cow and initiation of incubation, was compared to NDF digestion determined in sacco at 48 h. Rumen inoculum from a single cow was utilized in a thrice replicated incubation with whole crop alfalfa, corn, cereal and sudangrass forages of a lower and higher quality. The same cow was used as the host for the in sacco bags. The in vitro procedure used a bulk procedure with 5.0 cm × 5.5 cm multi-weave polyethylene polyester polymer bags that retained particles of 25 mm and larger. The in sacco procedure used the same bags retained in a large mesh bag. A within-day time delay of up to 6.5 h between collection of rumen fluid from the cow and initiation of in vitro fermentation had no impact on measured 48 h in vitro digestion of NDF. In contrast, no temperature dependent storage procedure maintained 48 h in vitro digestion of NDF at levels determined with no 48 h storage, although high quality alfalfa was least affected by any storage procedure. The 48 h in vitro digestion of NDF, determined using the minimum time delay between collection from the cow and initiation of the incubation, was higher than values obtained in sacco. Results show that this bulk in vitro procedure resulted in higher 48 h digestion of NDF than those determined with a similar in sacco procedure, thereby suggesting that laboratories located some distance from the donor animal can utilize in vitro procedures to accurately estimate 48 h digestion of NDF. However, storage of rumen fluid for 48 h, by any temperature dependent procedure examined, in order to facilitate fewer trips to the donor animal, or trips of substantially longer duration, will underestimate 48 h digestion of NDF to an extent that depends upon the forage incubated.     

In Vitro Study and Comparison of Caecal Methanogenesis and Fermentation Pattern in the Brown Hare (Lepus europaeus) and Domestic Rabbit (Oryctolagus cuniculus)

The brown hare and the domestic rabbit are mid-sized herbivorous mammals and hindgut fermenters, though their digestive physiologies differ in some traits. The objective of this study was to estimate and compare the caecal microbial activity in hares and rabbits via an analysis of the following end-products of in vitro caecal fermentation: methane, total gas production, short chain fatty acids and ammonia concentration. Hare caecal methanogenesis occurred at a much lower level (0.25 mmol/kg for samples incubated without substrate and 0.22 mmol/kg for samples incubated with substrate) than that of the rabbit (15.49 and 11.73 mmol/kg, respectively) (P<0.001). The impact of the substrate’s presence on caecal methanogenesis was not significant, though its presence increased the total gas production during fermentation (P<0.001). Hare caecal microflora produced a lower short chain fatty acids concentration than did rabbit microorganisms (P<0.05). In unincubated hare samples, the short chain fatty acids concentration was 28.4 mmol/kg, whereas in unincubated rabbit samples, the short chain fatty acids concentration was 51.8 mmol/kg. The caecal fermentation pattern of the hare was characterised by higher propionate and isobutyrate molar proportions compared with those observed in rabbit caecum (P<0.01). No significant changes in the ammonia concentration in either rabbit or hare caecum were found. The results obtained indicate some differences in the activity of the microbial populations colonising the hare and rabbit caecum, particularly in regards to methanogenic Archaea.     

Effect of mannanoligosaccharides supplementation on caecal microbial activity of rabbits

A total of 200 weaned (35 days) hybrid Hyla rabbits were randomly divided among five groups housed in bicellular cages (20 cages per group). Between 35 and 60 days of age, the groups were submitted to the following treatments: group ANT (positive control) fed a basal diet supplemented with antibiotics (colistin sulphate, 144 mg/kg; tylosin, 100 mg/kg; and oxytetracyclin, 1000 mg/kg); groups MOS_0.5, MOS_1.0 and MOS_1.5 fed the basal diet supplemented with 0.5, 1.0 and 1.5 g/kg mannanoligosaccharides (MOS), respectively; another group fed the basal diet without antibiotics or mannanoligosaccarides supplementation (negative control). Along the trial, an episode of epizootyc rabbit enteropathy occurs so that in the control group mortality rate was very high (78%) and survivor rabbits showed severe symptoms of disease (diarrhoea). Thus, the control group was discarded from the trial. At 60 days of age, samples of caecal content were collected from 10 rabbits per group and used as inocula for an in vitro gas production trial. At the end of fermentation (120 h of incubation), organic matter digestibility (OMd), cumulative gas production, fermentation kinetics, pH, volatile fatty acid (VFA) and NH3 productions were measured. Inoculum from MOS_1.0 rabbits showed the significant higher values of OMd (64.21%, P < 0.05), gas production (262.32 ml/g, P < 0.05), acetate (96.99 mmol/g OM, P < 0.05) and butyrate (26.21 mmol/g OM, P < 0.05) than the other groups. Slight differences were recorded among the groups ANT, MOS_0.5 and MOS_1.5. In addition, branched chain acids, in proportion to total VFAs, were significantly higher in MOS_1.0 inoculum (0.04, P < 0.05). MOS are able to affect fermentation activity of caecal micro-organism, but their activities seem not proportional to their level in the diet.     

Digestive efficiency of the Hoatzin, Opisthocomus hoazin: a folivorous bird with foregut fermentation

The Hoatzin Opisthocomus hoazin is the only known bird with a well-developed foregut plant fermentation system; most fermentation takes place in the crop and caudal oesophagus. To test Hoatzin digestive efficiency, balance (total collection) trials with captive Hoatzins were made using two experimental diets of different composition and fibre content. Dry matter (DM) intakes were similar for the diets (mean = 62.8 g DM/kg body mass/ day). Average DM, organic matter and nitrogen digestibilities were not significantly different between diets, with average values of 72.9%, 75.0% and 78.3%, respectively. In vitro organic matter digestibilities by cow ruminal inoculum were very similar to organic matter digestibilities in live Hoatzins for both diets. Fibre digestibility was among the highest recorded for herbivorous birds. Cellulose and acid detergent fibre digestibilities were 58.8% and 52.7%, respectively. Neutral detergent fibre (NDF) digestibility differed among diets—the higher the NDF content of the diet, the higher the NDF digestibility. The NDF digestibilities were 37.9% and 70.9% for the two diets with NDF concentrations of 32.4% and 37.3%, respectively. Differences in NDF digestibility can be attributed to the different concentrations of hemicellulose in the experimental diets. The high overall digestibility by captive Hoatzins is higher than values previously reported for other avian herbivores but similar to those of foregut-fermenting mammals on similar diets. The unique digestive strategy of the Hoatzin maximizes digestion of cell wall and cell contents. The high digestive efficiency in the Hoatzin is not predicted by allometric models of fibre digestion as a function of body mass. Other nutritional benefits, such as detoxification of plant secondary compounds and microbial synthesis of essential amino acids and vitamins, may explain the evolution of foregut fermentation in this avian folivore.     

The Effect of Rumen and Post-Rumen Feeding of Carbohydrates on the Caecal Microflora of Sheep

S ummary . When sheep were bottle-fed with solutions of glucose, sucrose or maltose, so avoiding fermentation in the rumen, there was a marked increase in the number of caecal bacteria, with a higher percentage of viable bacteria, compared with caecal counts from sheep fed conventionally on carbohydrates. Bottle-feeding also resulted in a redistribution of bacterial types, 40–46% of the flora comprising Gram positive rods and a significant increase in butyric acid and decrease in propionic acid in the caecal contents. Feeding cellulose suspensions by bottle or conventionally failed to produce significant differences in counts of cellulolytic caecal bacteria. When sucrose was infused in increasing amounts into the abomasum, Streptococcus bovis was the principal organism, isolated from faeces.     

In vivo study of cecal fermentation activity in the rabbit. Completion and validation of a new technique for cecal cannulation]

A new technique for caecal cannulation in adult rabbit was validated in order to perform in vivo studies of caecal fermentation under a physiological status. The cannulation did not modify the digestibility of the diet, and it was possible to collect digesta (10 g fresh matter) after a few minutes without stress for animals only 10 days post-surgery. Volatile fatty acid (VFA) (60 mM/l) and ammonia (11 mM/l) concentration of caecal digesta collected in vivo was not different from that obtained from slaughtered rabbits. VFA measurements were reproducible (CV = 6.8%) and were not dependent on the daily collection frequency (1-5/day). Caecal VFA level in the starved rabbit was very low (23 mM/l) while the butyrate/propionate rate was the inverse (C4/C3 = 0.6). Five h after feeding, the in vivo VFA level reached 96 mM/l and the butyrate proportion (12%) over-reached those of propionate (3.5%). The caecal fermentations of a 7-week-old rabbit differed from those of an adult by a higher VFA level and by a greater post-feeding variation in the fermentation pattern.     

Rumen Fungi and Forage Fiber Degradation

The role of anaerobic rumen fungi in in vitro forage fiber degradation was determined in a two forage × two inoculum source × five treatment factorial design. Forages used as substrates for rumen microorganisms were Coastal bermuda grass and alfalfa; inoculum sources were rumen fluid samples from a steer fed Coastal bermuda grass hay or alfalfa hay; treatments were whole rumen fluid (WRF), WRF plus streptomycin (0.2 mg/ml of rumen fluid) and penicillin (1.25 mg/ml of fluid), WRF plus cycloheximide (0.5 mg/ml of fluid), WRF plus streptomycin, penicillin, and cycloheximide, and McDougall buffer. Populations of fungi as shown by sporangial development were greater on bermuda grass leaves than on alfalfa leaflets regardless of inoculum source. However, endogenous fungal populations were greater from the alfalfa hay inoculum. Cycloheximide inhibited the fungi, whereas streptomycin and penicillin, which inhibit bacterial populations, resulted in an increase in numbers of sporangia in the alfalfa inoculum, suggesting an interaction between bacteria and fungi. Bacteria (i.e., WRF plus cycloheximide) were equal to the total population in degrading dry matter, neutral-detergent fiber (NDF), acid-detergent fiber (ADF), and cellulose for both inocula and both forages. Degradation of dry matter, NDF, ADF, and cellulose by anaerobic fungi (i.e., WRF plus streptomycin and penicillin) was less than that due to the total population or bacteria alone. However, NDF, ADF, and cellulose digestion was 1.3, 2.4, and 7.9 percentage units higher, respectively, for bermuda grass substrate with the alfalfa versus bermuda grass inoculum, suggesting a slight benefit by rumen fungi. No substantial loss of lignin (72% H₂SO₄ method) occurred due to fungal degradation. The most active fiber-digesting population in the rumen was the bacteria, even when streptomycin and penicillin treatment resulted in an increase in rumen fungi over untreated WRF. The development of large numbers of sporangia on fiber may not indicate a substantial role as digesters of forage.     

The effect of rabbit age on in vitro caecal fermentation of starch, pectin, xylan, cellulose, compound feed and its fibre

In vitro gas production kinetics of six different substrates, pectin (PEC), xylan (XYL), starch (STA), cellulose (CEL), commercial compound feed (FEED; 201 g crude protein per kg, 155 g crude fibre per kg, 334 g neutral-detergent fibre (NDF) per kg and 190 g acid-detergent fibre (ADF) per kg) and an NDF prepared from commercial compound feed (NDF_FEED) were determined using the caecum contents of weaned rabbits (36 days of age) and of rabbits at slaughter age (78 days of age) as inoculums. The cumulated gas production over 96 h of incubation was modelled with Gompertz model, and the kinetic parameters compared. The total potential gas production (parameter ‘B’ of the Gompertz model) was not affected (P>0.05) by the inoculum source, except with STA, where rabbits at slaughter weight had significantly higher total potential fermentability (314 ml/g dry matter (DM)) than those at weaning age (189 ml/g DM). Intensities of fermentation (maximum fermentation rate; MFR) of PEC (32.2 ml/h) and XYL (24.4 ml/h) were significantly greater in rabbits at weaning, while that of STA (45 ml/h) was significantly lower than at slaughter age (23.0, 14.3 and 14.0 ml/h for PEC, XYL and STA, respectively). The MFRs of CEL and NDF_FEED were very similar between inoculum sources. In the first 10 h of fermentation which correspond to the normal retention time of the substrates in the caecum, the highest amount of gas was produced from PEC, followed by FEED and XYL. These substrates had a time of maximum fermentation rate (TMFR) at both rabbit ages short enough (8.0 and 9.5 h for PEC, 9.5 and 6.6 h for FEED, 13.7 and 14.2 h for XYL at weaning and at slaughter age, respectively) to be almost completely fermented in vivo.     

In Vitro Stimulation of Forage Fiber Degradation by Ruminal Microorganisms with Aspergillus oryzae Fermentation Extract

Aspergillus oryzae fermentation extract (Amaferm) was evaluated for its ability to influence degradation of brome grass and switchgrass fiber fractions by mixed ruminal microorganisms in vitro. Addition of Amaferm at a concentration of 0.067 mg/ml, which is approximately the concentration found in the rumen ecosystem (0.06 mg/ml), increased the degradation of brome grass neutral detergent fiber (NDF) by 28% after fermentation for 12 h (P < 0.01), but had no effect after fermentation for 24 or 48 h. The levels of degradation of both the cellulose and hemicellulose fractions were increased after fermentation for 12 h (P < 0.01). Additions of 0.08 and 8% (vol/vol) Amaferm filtrate (12.5 g/100 ml) stimulated degradation of switchgrass NDF by 12 and 24% (P < 0.01), respectively, after fermentation for 12 h; when 80% filtrate was added, degradation was decreased by 38%. The concentrations of total anaerobes in culture tubes containing 80% filtrate were 5 times greater than the concentrations in the controls; however, the concentrations of cellulolytic organisms were 3.5 times lower than the concentrations in the controls (P < 0.05). These results suggested that the filtrate contained high concentrations of soluble substrate which did not allow the cellulolytic organisms to compete well with other populations. The remaining concentrations of esterified p-coumaric and ferulic acids were lower at 12 h in NDF residues obtained from fermentation mixtures supplemented with Amaferm. Because the total anaerobes were not inhibited in fermentation mixtures containing Amaferm, antibiotics are unlikely to be involved as a mode of action for increasing NDF degradation. The possibility that Amaferm contains enzymes (possibly esterases) that may play a role in stimulating the rate of fiber degradation by mixed ruminal microorganisms by removal of plant cell wall phenolic acid esters is discussed.     

Determination of polyphenol and crude nutrient content and nutrient digestibility of dried and ensiled white and red grape pomace cultivars

The present study aimed to determine the nutrient and energy content of fresh and ensiled grape pomace (GP) from different grape varieties originating from Germany, and to estimate the feed value of dried white, dried red and ensiled white GP by calculating nutrient digestibility and the content of metabolisable energy (ME) and net energy lactation (NEL) measured in sheep as a ruminant model. GP from red cultivars had higher contents of organic matter (OM), crude protein (CP), ether extract (EE), crude fibre (CF), total phenolic contents (TPC) and ME, whereas the concentrations of ash and sugar were lower than from white cultivars. Compared with untreated GP, ensiled GP had increased concentrations of CP (+19%), ether extract (EE; +23%) and CF (+12%) and a higher ME content (+7%) and markedly decreased concentrations of sugar (?99.6%) and TPC (?48%). The concentrations of dry matter, OM and ash were not different between ensiled and fresh GP. Compared with dried GP, ensiled GP had a higher nutrient digestibility (OM, +32%; CP, +43%; CF, +46%; neutral detergent fibre [NDF], +54%; acid detergent fibre [ADF], +69%) and higher energy values (ME, +16%; NEL, +19%). The digestibility of OM, CP, EE and CF and the energy content were higher for dried red than for dried white GP, whereas the digestibility of NDF_OM and ADF_OM was lower for dried red than dried white GP. In conclusion, the results show that both red and white GP are suitable dietary sources for enrichment with TPC. Furthermore, compared with drying ensiling of GP improves the feeding value of GP and is a good possibility of preserving the seasonally produced by-product of winemaking for ruminant feeding.     

Effect of glyphosate contaminated feed on rumen fermentation parameters and in sacco degradation of grass hay and corn grain

Abstract Four rumen fistulated wethers were used to investigate the effect of glyphosate contaminated feed on rumen fermentation. The rations were based on corn silage, urea and a vitamin-mineral premix, either in the absence or presence of 0.77 g glyphosate per kg DM. Furthermore, rations were fed either with or without aromatic amino acid supplementation. During four periods of 28 days, sheep received each of the four dietary treatments according to a Latin square. After 14 days of adaptation rumen fermentation parameters (pH, ammonia, volatile fatty acids) were measured on day 15 over a five-hour period after the morning feeding. The remaining 13 days served for in sacco degradation studies with grass hay and corn grain. Ammonia (NH3) and pH of rumen fluid were within the normal range for all dietary treatments (NH3: 9.1-32.3 mmol x l(- l), pH: 6.2-6.7). Neither rumen fermentation parameters nor in sacco DM and NDF degradation of incubated feedstuffs were significantly affected by glyphosate, with or without aromatic amino acid supplementation. Kinetic profiles of the in sacco dry matter and NDF degradation of grass hay were almost identical for the dietary treatments.     

Fibre utilization by Kalahari dwelling subterranean Damara mole-rats (Cryptomys damarensis) when fed their natural diet of gemsbok cucumber tubers (Acanthosicyos naudinianus)

Kalahari dwelling Damara mole-rats (Cryptomys damarensis) naturally feed on a high fibre diet of underground gemsbok cucumber tubers, Acanthosicyos naudinianus. We investigated the degree of fibre utilization and fermentation on this diet by measuring caecal characteristics (namely temperature, pH and weight) and in vitro rates of gas and short chain fatty acid (SCFA) production in these underground dwelling hind-gut fermentors. Rectal temperatures (33.8±0.6°C) were consistently higher than caecal temperatures (33.3 ± 0.6°C). Furthermore, a 0.8°C gradient of temperatures existed within the caecum, with the lowest temperature occurring in the corpus caeci. Both rates of gas production (4.74 ± 0.6 ml/g dry matter/hr) and SCFA production (266.80 ± 9.251 /i mol/caecum per hr) were high, with proportionately more acetic acid produced than any other SCFA. Nevertheless, the initial concentrations of SCFAs present in the caecum were low (52 ±17 mM) implying a rapid rate of absorption of these SCFAs. The high rates of fermentation provide a considerable amount of energy that would otherwise be trapped in fibre and thus unavailable to the animal. This highly efficient caecal fermentation enables the Damara mole-rat to maximally exploit the underground food resources in the arid-zone ecotope.     

Effect of glyphosate contaminated feed on rumen fermentation parameters and in sacco degradation of grass hay and corn grain

Four rumen fistulated wethers were used to investigate the effect of glyphosate contaminated feed on rumen fermentation. The rations were based on corn silage, urea and a vitamin-mineral premix, either in the absence or presence of 0.77?g glyphosate per kg DM. Furthermore, rations were fed either with or without aromatic amino acid supplementation. During four periods of 28 days, sheep received each of the four dietary treatments according to a Latin square. After 14 days of adaptation rumen fermentation parameters (pH, ammonia, volatile fatty acids) were measured on day 15 over a five-hour period after the morning feeding. The remaining 13 days served for in sacco degradation studies with grass hay and corn grain. Ammonia (NH₃) and pH of rumen fluid were within the normal range for all dietary treatments (NH₃: 9.1 – 32.3?mmol·l^???1, pH: 6.2 – 6.7). Neither rumen fermentation parameters nor in sacco DM and NDF degradation of incubated feedstuffs were significantly affected by glyphosate, with or without aromatic amino acid supplementation. Kinetic profiles of the in sacco dry matter and NDF degradation of grass hay were almost identical for the dietary treatments.     

Comparison of fermentation reactions in different regions of the human colon.

Colonic contents were obtained from two human sudden-death victims within 3 h of death. One of the subjects (1) was methanogenic, the other (2) was a non-CH4 producer. Measurements of bacterial fermentation products showed that in both individuals short-chain fatty acids, lactate and ethanol concentrations were highest in the caecum and ascending colon. In contrast, products of protein fermentation, such as ammonia, branched chain fatty acids and phenolic compounds, progressively increased from the right to the left colon, as did the pH of gut contents. In Subject 1, cell population densities of methanogenic bacteria (MB) increased distally through the gut and methanogenic activity was lower in the right (0.78-1.18 mumol CH4 produced/h/g dry wt contents) than in the left colon (1.34 mumol CH4 produced/h/g dry wt contents). Methane production rates did not correlate with MB numbers. Sulphate-reducing bacteria (SRB) were not found and dissimilatory sulphate reduction was not detected in any region of the colon. Methanogenic bacteria did not occur in subject 2, but high numbers of SRB were present throughout the gut (ca 10(9)/g dry wt contents). Sulphate reduction rates were maximal in the ascending and transverse colons (0.24 and 0.22 mumol 35SO4(2-) reduced/h/g dry wt contents, respectively). Short-chain fatty acid production by caecal contents was up to eight-fold higher than contents from the sigmoid/rectum. These findings demonstrate significant differences in fermentation reactions in different regions of the large gut.     

Optimization of process variables for minimization of byproduct formation during fermentation of blackstrap molasses to ethanol at industrial scale

Aims: To investigate the effect of molasses concentration, initial pH of molasses medium, and inoculum’s size to maximize ethanol and minimize methanol, fusel alcohols, acetic acid and aldehydes in the fermentation mash in industrial fermentors. Methods and Results: Initial studies to optimize temperature, nitrogen source, phosphorous source, sulfur supplement and minerals were performed. The essential nutrients were urea (2 kg in 60 m³), 0·5 l each of commercial phosphoric acid and sulfuric acid (for pH control) added at the inoculum preparation stage only. Yields of ethanol, methanol, fusel alcohols, total acids and aldehydes per 100‐l fermentation broth were monitored. Molasses at 29°Brix (degree of dissolved sugars in water), initial pH 4·5, inoculum size 30% (v/v) and anaerobic fermentation supported maximum ethanol (7·8%) with Y_P/S = 238 l ethanol per tonne molasses (96·5% yield) (8·2% increase in yield), and had significantly lower values of byproducts than those in control experiments. Conclusions: Optimization of process variables resulted in higher ethanol yield (8·2%) and reduced yield of methanol, fusel alcohols, acids and aldehydes. Significance and Impact of the Study: More than 5% substrate is converted into byproducts. Eliminating or reducing their formation can increase ethanol yield by Saccharomyces cerevisiae, decrease the overall cost of fermentation process and improve the quality of ethanol.     

Digesta characteristics of dorsal, middle and ventral rumen of cows fed with different hay qualities and concentrate levels

The influence of fibre content of hay (H) and concentrate level (C) on local differences in the composition of ruminal digesta (ratio of solid to fluid digesta, DM, NDF, ADF and ADL content), particle size (MPL), specific gravity (SG) and fermentation (pH and concentrations of SCFA and bicarbonate) have been tested on two ruminally cannulated Friesian cows (520 kg BW) which were fed restricted, using individual cows as experimental units. Digesta samples were collected via cannula from three rumen layers: 5 to 10 cm (top) and 25-35 cm beneath the top of the particle mat (middle) and 5-10 cm above the rumen floor (bottom). For a main plot treatment (H x C), repeated samples were collected at four time intervals (1 h before and 2, 5 and 10 h after morning feeding) on each of two days. From top to bottom rumen the share of solid digesta mass (SM), DM and NDF contents of squeezed digesta fluid (SRF) and concentration of SCFA decreased (P < 0.05); pH and bicarbonate concentration increased (P < 0.05), while DM, NDF, ADF and ADL contents in SM, MPL and SG did not differ. Higher NDF content of hay (from 47-62%) increased SM, fibre fractions in SM, MPL, pH and concentration of bicarbonate in ruminal digesta, especially when 50% concentrate was given, while SG decreased. When the concentrate level was enhanced from 20 to 50%, digesta SM, MPL and the content of DM and NDF in SRF increased, while pH, concentrations of SCFA and acetate decreased when low-fibre hay was given. With longer time after feeding the digesta SM was reduced and fibre content in SM increased. The increase of the fibre content of hay reduced the possible negative effect of high concentrate level on the stratification of ruminal digesta. The decrease of the fibre content of hay promised better conditions for fibre digestion in the rumen when concentrate availability is limited.     

Phytase production and decrease of phytic acid content in canola meal byAspergillus carbonarius in solid-state fermentation

Solid-state fermentation (SSF) usingAspergillus carbonarius with canola meal as a substrate showed that production of phytase was associated with growth; maximum activity was achieved after 72 h. Apparent 25% and 10% increases in the protein content of the canola meal were noticed after 48 h and 72 h, respectively but total carbohydrate concentration had fallen by 25% by the end of fermentation. The rate of decrease of phytic acid content was optimum with a moisture content between 53% and 60%; homogenization of the inoculum for 120 s led to the greatest biomass and lowest phytic acid content. Inoculation of sterile meal led to lower phytic acid contents than inoculation of non-sterile meal.The authors are with the Department of Chemical Engineering, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada     

Using microbial fatty acids to improve understanding of the contribution of solid associated bacteria to microbial mass in the rumen

This study sought to distinguish liquid-(LAB) and detached (SAB₁) and undetached (SAB₂) solid-associated bacteria through their fatty acid (FA) and purine base (PB) profiles. Fatty acids and PB were also evaluated as internal microbial markers for estimating microbial biomass associated with rumen particles. Four merino rams fitted with rumen cannulae and fed dehydrated alfalfa pellets provided rumen contents. In 3 consecutive weeks, rumen contents were collected and samples of LAB and SAB₁, total rumen content (TRC), washed rumen particles (WRP) and rumen particles after SAB₁ extraction (ERP) were obtained and analysed for PB and FA. The SAB₂ biomass composition was estimated from the non-NDF organic matter (OM) remaining in ERP. The concentration of total SAB biomass in particles was estimated using both PB and odd and branched-chain fatty acids (OBCFA). Concentrations of PB and OBCFA were highly correlated among the different rumen fractions. Marked differences between LAB and SAB populations occurred with LAB having higher PB content, lower FA content and a higher proportion (g/100 g fatty acids) of OBCFA than did SAB. The chemical composition of SAB₁ and SAB₂ was similar, except for the 15% higher crude protein content of the latter. The concentration of OBCFA (mg/g microbial OM) did not differ between bacterial fractions. The PB/OBCFA ratio (mg/mg) was higher in LAB (2.08) than in SAB (0.94). The ratio between branched-chain and odd-linear-chain FA was higher in LAB (2.26) than in SAB (1.46). Extraction of PB and OBCFA from WRP with our SAB detachment procedure was 61% and 31%, respectively. Estimated SAB₁ and total SAB biomass (mg OM/g WRP) were 158 and 266, and 47 and 164, respectively, using PB and OBCFA as microbial markers. This study suggests that the OBCFA have potential as internal microbial markers in rumen ecosystem studies.