Application of response surface methodology for optimization of acidogenesis of cattail by rumen cultures

Acidogenesis of cattail using rumen cultures was carried out to produce volatile fatty acids (VFA) in this study. The influences of pH and substrate concentration on cattail degradation, VFA yield and microbial growth were investigated by using response surface methodology (RSM). Experimental results showed that a low substrate concentration and pH of 6.9 were optimal for acidogenesis of cattail. The highest cattail degradation efficiency, VFA yield and microbial yield were 75.9%, 0.41 g/g VS and 0.110 g/g VS, respectively. Further experiments confirmed that the main VFA in the acidogenesis of cattail were acetate, propionate and butyrate, while i-butyrate, valerate and i-valerate were also produced at low levels. The results suggested that acidogenesis using rumen cultures is a promising method for cattail disposal.     

Comparative studies on the degradation and mean retention time of solid and liquid phases in the forestomachs of dromedaries and sheep fed on low-quality roughages from Tunisia

The digestion of the acid detergent fiber (ADF) fraction of vetch-oat hay was studied in two dromedaries and three sheep, all rumen-fistulated and fed vetch-oat hay with a concentrate. Dromedaries and sheep consumed similar amounts of feed dry matter (DM) per kilogram of metabolic weight, but dromedaries drank less water than sheep. There were no differences in the volatile fatty acid (VFA) and ammonia concentrations in the rumen between dromedaries and sheep, but pH was higher in the dromedaries than in the sheep (P < 0.05). The mixture of VFA contained more propionate and butyrate and less acetate in dromedaries than in sheep (P < 0.05). The protozoal concentration was higher in the rumen of sheep than of dromedaries. This result was consistent with the higher N---NH₃, concentration in sheep. Entodinium was the most abundant species in both dromedaries and sheep. Specific rates of rumen liquid (PEG) and particle (chromium-mordanted hay) outflow were higher and lower, respectively, in dromedaries than in sheep. Also, dromedaries had higher in sacco, in vitro, and fecal digestibilities of vetch-oat hay dry matter (DM) and ADF than sheep. In sacco, the potential degradable fraction was higher, but the rate of degradation was not. The greater utilization of ADF in the rumen by dromedaries is discussed in relation to the higher cellulolytic activity of the rumen microorganisms, the longer retention time of feed particles and/or the greater buffering capacity of the rumen contents of the dromedary against fermentation acids.     

Effects of monensin on volatile fatty acid metabolism in periparturient dairy cows using compartmental analysis

Eight multiparous periparturient Holstein cows fitted with ruminal cannulas were used in a split plot design to evaluate effects of monensin on ruminal volatile fatty acid (VFA) metabolism. Diets were supplemented with 300 mg/day of monensin, or no monensin, both prepartum and postpartum. Isotopic tracers, Na-1-¹³C-acetate (Ac), Na-1-¹³C-propionate (Pr), or Na-1-¹³C-butyrate (Bu) were used as markers to describe VFA kinetics in the rumen. The Windows version of SAAM software (WinSAAM) was used to develop a steady state VFA model. A 9-compartment model was adequate to comprehensively describe ruminal VFA metabolism. The main VFA compartments consisted of Ac, Pr and Bu. The model estimated lower Bu and Ac interconversions with monensin, postpartum (Bu to Ac; 0.14 versus 0.12; P=0.04, and Ac to Bu; 0.32 versus 0.25; P=0.11) compared to when measured prepartum. Results demonstrate that dilution studies employing stable isotopes of VFA can be used to provide information on VFA metabolism of the periparturient dairy cow. A time frame of 320 min of labeled VFA infusion employing a single injection allows accurate quantification of VFA metabolism in the rumen. Compartmental kinetic analysis of major VFA in the rumen indicate that monensin reduced about 0.125 the portion of the Ac that contributes to Bu by reducing movements of Bu originated carbons to the Ac pool. Monensin may affect certain biochemical pathways of interconversion of Bu and Ac in the rumen. Propionate kinetic data suggests that Pr behaves as a single pool in the rumen. Monensin did not affect Pr production in the rumen suggesting that monensin improves the metabolic status of the transition cow in a way other than increasing Pr production in the rumen.     

Factors influencing biohydrogenation and conjugated linoleic acid production by mixed rumen fungi

The objective of this study was to evaluate the effect of soluble carbohydrates (glucose, cellobiose), pH (6.0, 6.5, 7.0), and rumen microbial growth factors (VFA, vitamins) on biohydrogenation of linoleic acid (LA) by mixed rumen fungi. Addition of glucose or cellobiose to culture media slowed the rate of biohydrogenation;only 35-40% of LA was converted to conjugated linoleic acid (CLA) or vaccenic acid (VA) within 24 h of incubation, whereas in the control treatment, 100% of LA was converted within 24 h. Addition of VFA or vitamins did not affect biohydrogenation activity or CLA production. Culturing rumen fungi at pH 6.0 slowed biohydrogenation compared with pH 6.5 or 7.0. CLA production was reduced by pH 6.0 compared with control (pH 6.5), but was higher with pH 7.0. Biohydrogenation of LA to VA was complete within 72 h at pH 6.0, 24 h at pH 6.5, and 48 h at pH 7.0. It is concluded that optimum conditions for biohydrogenation of LA and for CLA production by rumen fungi were provided without addition of soluble carbohydrates, VFA or vitamins to the culture medium; optimum pH was 6.5 for biohydrogenation and 7.0 for CLA production.     

Degradation of mimosine, 2,3-dihydroxy pyridine and 3-hydroxy-4(1H)-pyridine by bacteria from the rumen of sheep in Venezuela

Abstract The addition of Leucaena leucocephala herbage did not diet of sheep in Venezuela did not affect the concentration of volatile fatty acids (VFA) in the rumen, the degradation of rice straw incubated in sacco, or the numbers of rumen fungi or bacteria. However, feeding Leucaena increased the concentration of ammonia in the rumen. In addition, two products of the degradation of the toxic amino acid mimosine were detected in the rumen when Leucaena was fed. One of these products, 2,3-dihydroxy pyridine (2,3-DHP), was detected at concentrations of up to 1.1 μmol/ml. The other, 3-hydroxy-4(1H)-pyridone (3,4-DHP) was found at concentrations of up to 0.96 μmol/ml. The examination of bacterial cultures isolated from the rumen of the sheep under investigation showed that feeding Leucaena increased the relative proportions of short Gram-negative rods and decreased the proportion of long roads and coccobacilli present. Although the animals fed Leucaena showed a small loss in weight during the feeding trial, no evidence of Leucaena toxicity was seen. A total of 18 cultures capable of degrading 2,3-DHP or 3,4-DHP were isolated from the rumen of the sheep before Leucaena was fed. These included both Gram-positive and Gram-negative bacteria, and a Gram-positive sporeformer. It seems that 2,3-DHP and 3,4-DHP may be degraded by a much wider range of bacteria than has been recognised previously. The detection of these bacteria before Leucaena was fed suggests that they were indigenous members of the rumen microflora of sheep in Venezuela.     

Modelling the implications of feeding strategy on rumen fermentation and functioning of the rumen wall

The present study gives a critique of the mechanisms involved with the formation of volatile fatty acid (VFA) formed in the lumen of the reticulo-rumen, the absorption of VFA across the reticulo-rumen wall, and the intra-epithelial metabolism of VFA by reticulo-rumen epithelium. In contrast to the empirical treatment of these aspects in previous rumen modelling studies, a mechanistic model was developed which represents each of these aspects separately. Because tissues of the reticulo-rumen may strongly adapt to changing nutritional conditions, this adaptive response was included in the model. The model enabled an evaluation of the implications of VFA yield on the development of the rumen wall, on the transport of VFA, on the extent of intra-epithelial metabolism of VFA, and on the consequences for the supply of VFA to the ruminant. The current modelling effort allowed the integration of existing knowledge on each of these aspects and the model reproduced some essential characteristics of experimental observations on VFA absorption and metabolism. Although further development is still needed, the model appears helpful to distinguish elements that require specific consideration when evaluating rates of net portal appearance of VFA, or when testing hypothesis on the interaction between formation, absorption and intra-epithelial metabolism of VFA under various experimental conditions.     

In vivo production and molar percentages of volatile fatty acids in the rumen: a quantitative review by an empirical approach

Despite their major contribution to the energy supply of ruminants, the production of volatile fatty acids (VFA) in the rumen is still poorly predicted by rumen models. We have developed an empirical approach, based on the interpretation of large bibliographic databases gathering published in vivo measurements of ruminal VFA production rate (PR), rates of duodenal and faecal digestion and molar percentages of VFA in the rumen. These databases, covering a wide range of intake levels and dietary composition, were studied by meta-analysis using within-experiment models. We established models to quantify response laws of total VFA-PR and individual VFA molar percentages in the rumen to variations in intake level and dietary composition. The rumen fermentable organic matter (RfOM) intake, estimated from detailed knowledge of the chemical composition of diets according to INRA Feed Tables, appears as an accurate explanatory variable of measured total VFA-PR, with an average increment of 8.03 ± 0.64 mol total VFA/kg RfOM intake. Similar results were obtained when total VFA-PR was estimated from measured apparent RfOM (total VFA-PR/RfOM averaging 8.3 ± 1.2 mol/kg). The VFA molar percentages were related to dry matter intake and measured digestible organic matter (OM), digestible NDF and rumen starch digestibility, with root mean square error of 1.23, 1.45, 0.88 and 0.41 mol/100 mol total VFA for acetate, propionate, butyrate and minor VFA, respectively, with no effect of pH on the residuals. Stoichiometry coefficients were calculated from the slopes of the relationships between individual VFA production (estimated from measured apparent RfOM and individual VFA molar percentages) and measured fermented fractions. Coefficients averaged, respectively, 66, 17, 14 and 3 mol/100 mol for NDF; 41, 44, 12 and 4 mol/100 mol for starch; and 46, 35, 13 and 6 mol/100 mol for crude protein. Their use to predict VFA molar percentages appear relevant for most dietary conditions, that is, when the digested NDF/digested OM ratio exceeded 0.12. This study provides a quantitative review on VFA yield in the rumen. It contributes to the development of feed evaluation systems based on nutrient fluxes.     

Establishment of cellulolytic bacteria and development of fermentative activities in the rumen of gnotobiotically-reared lambs receiving the microbial additive Saccharomyces cerevisiae CNCM I-1077

We studied the effects of a yeast additive used in ruminant nutrition on the establishment of cellulolytic bacteria, on plant cell wall degradation and on digestive functions in the rumen of gnotobiotically-reared lambs. Cellulolytic bacteria inoculated to the lambs tended to become established earlier in the presence of Saccharomyces cerevisiae CNCM I-1077 (SC). In addition, their population was maintained at a higher level, when the physico-chemical conditions of the biotope were altered. In these lambs, specific activities of fibrolytic enzymes were greater, and in sacco degradation of wheat straw tended to increase. In the presence of SC there was a decrease in ruminal ammonia concentration and a higher volatile fatty acid (VFA) concentration when lambs were 20 to 50 days old. These data suggest that this yeast strain may stimulate the development of cellulolytic microflora and enhance microbial activity in the rumen of young ruminants. Such activity could be beneficial in preventing microbial imbalance and a reduction of rumen function efficiency in the case of nutritional transitions. Further studies with conventional animals will soon be performed in order to verify these dings.     

Effects of nitro compounds and feedstuffs on in vitro methane production in chicken cecal contents and rumen fluid

Short-chain volatile fatty acids (VFA) and methane are the products from a wide variety of microorganisms living in the gastrointestinal tract. The objective of this study was to examine effects of feedstuff and select nitro compounds on VFA and methane production during in vitro incubation of laying hen cecal contents and rumen fluid from cattle and sheep. In the first experiment, one of the three nitro compound was added to incubations containing cecal contents from laying hens supplemented with either alfalfa (AF) or layer feed (LF). Both feed material influenced VFA production and acetic acid was the primary component. Incubations with nitro ethanol and 2-nitropropanol (NP) had significantly (P<0.05) higher propionate concentrations than incubations with added nitroethane (NE). The results further indicated that incubations containing LF produced significantly (P<0.05) more butyrate than incubations with added AF. Addition of NP and LF to incubations of avian cecal flora may promote Gram-positive, saccharolytic, VFA-producing bacteria, especially Clostridium spp. which is the predominant group in ceca. Similar to VFA production, both feed materials fostered methane production in the incubations although methane was lower (P<0.05) in incubations with added nitro compound, particularly NE. In experiments 3-8, NE was examined in incubations of bovine or ovine rumen fluid or cecal contents containing either AF or LF. Unlike cecal contents, LF significantly (P<0.05) supported in vitro methane production in incubations of both rumen fluids. The results show that NE impedes methane production, especially in incubations of chicken cecal contents.     

Correlation between composition of the bacterial community and concentration of volatile fatty acids in the rumen during the transition period and ketosis in dairy cows

The transition period is a severe challenge to dairy cows. Glucose supply cannot meet demand and body fat is mobilized, potentially leading to negative energy balance (NEB), ketosis, or fatty liver. Propionate produces glucose by gluconeogenesis, which depends heavily on the number and species of microbes. In the present study, we analyzed the rumen microbiome composition of cows in the transition period, cows with ketosis, and nonperinatal cows by terminal restriction fragment length polymorphism (TRFLP) analysis of 16S rRNA genes and quantitative PCR. TRFLP analysis indicated that the quantity of Veillonellaceae organisms was reduced and that of Streptococcaceae organisms was increased in rumen samples from the transition period and ketosis groups, with the number of Lactobacillaceae organisms increased after calving. Quantitative PCR data suggested that the numbers of the main propionate-producing microbes, Megasphaera elsdenii and Selenomonas ruminantium, were decreased, while numbers of the main lactate-producing bacterium, Streptococcus bovis, were increased in the rumen of cows from the transition period and ketosis groups, with the number of Lactobacillus sp. organisms increased after calving. Volatile fatty acid (VFA) and glucose concentrations were decreased, but the lactic acid concentration was increased, in rumen samples from the transition period and ketosis groups. Our results indicate that the VFA concentration is significantly related to the numbers of Selenomonas ruminantium and Megasphaera elsdenii organisms in the rumen.     

Feeding behavior, rumination, reticulo-ruminal fermentation and plasma volatile fatty acids, compared in goats and sheep; influence of the diet

Two-year old Alpine she-goats (n = 3) and Texel ewes (n = 3) were compared as to eating behaviour, rumination and volatile fatty acids (VFA) in rumen and blood. The animals were fed once daily with two different proportions (20 and 80%) of barley and hay. Dry matter intake was fixed at 48 g D.M/kg P0.75 per day. In similar feeding and environmental conditions, eating behaviour and rumination of goats and sheep did not differ much: the goats tended to eat faster and there were more rumination periods in the sheep. Latency time, mean duration of rumination periods, daily rumination time and circadian pattern of rumination did not differ significantly between the two species (fig. 1). With both diets we observed a higher VFA concentration and a lower acetate/propionate ratio in the rumen of the ewes; however, rumen pH was lower only in those eating the 80% barley ration (fig. 2). Blood VFA in the jugular vein did not differ between sheep and goats (fig. 3). The proportion of cereals and hay in the diets affected rumen fermentation and rumination pattern in both species. With a higher concentrate/roughage ratio, rumen and plasma VFA increased, while the pH and acetate/propionate ratio in the lumen juice, the number of rumination periods and daily rumination time decreased. When the animals were fed the 80% barley ration, there was practically no rumination in the first 9 h after the single meal. During this time, rumen pH was minimal and VFA levels in the rumen and blood were maximal.     

Rumen chemical and bacterial changes during stepwise adaptation to a high-concentrate diet in goats

The correlation between rumen chemical and bacterial changes was investigated during a four periodical stepwise adaptation to a high-concentrate diet (concentrate level at 0%, 30%, 50% and 70% for diet I to IV, respectively) in goats. The results showed that ruminal pH decreased from 6.7 to 5.5 after switching from diet I to II, and was maintained at about 5.5 on diet III. Denaturing gradient gel electrophoresis results showed that the rumen bacterial community was relatively stable during the initial three feeding periods, except for the appearance of three bands when diet changed from I to II, suggesting that an appropriate concentrate level can promote the proliferation of some bacteria. After 12 days of feeding diet III, total volatile fatty acid (VFA) concentration and butyrate proportion decreased. At days 2 and 3 of feeding diet IV, ruminal pH declined sharply to 5.3 and 4.7, respectively, and total VFA concentration decreased further while lactic acid concentration increased markedly, suggesting a relation between lactic acid accumulation and ruminal pH decline. At the same time, many bacteria disappeared, including most fibrolytic-related bacteria while Streptococcus bovis and Prevotella-like species dominated. Interestingly, Succinivibrio dextrinosolvens-like species maintained throughout the experiment, suggesting its tolerance to low pH. In conclusion, rumen bacterial community was relatively stable feeding 0% to 50% concentrate diets, and it was observed that appropriate concentrate levels in the diet could increase the diversity of rumen bacteria. However, concentrate-rich diets caused lactic acid accumulation and low ruminal pH that caused the disappearance of most fibrolytic-related bacteria sensitive to low pH while S. bovis and genus Prevotella persisted.     

Effects of hops (Humulus lupulus L.) extract on volatile fatty acid production by rumen bacteria

Aims: To determine the effects of hops extract on in vitro volatile fatty acid (VFA) production by bovine rumen micro‐organisms. Methods and Results: When mixed rumen microbes were suspended in media containing carbohydrates, the initial rates of VFA production were suppressed by β‐acid‐rich hops extract. The rates of VFA production increased over extended incubations (24 h), and hops extract caused an increase in the propionate to acetate ratio. Hops extract inhibited the growth and metabolism of Streptococcus bovis, but Selenomonas ruminantium and Megasphaera elsdenii were not affected. Likewise, the propionate production of M. elsdenii/S. bovis co‐cultures, but not M. elsdenii/S. ruminantium co‐cultures, was decreased in the presence of hops extract. Conclusions: These results are consistent with the hypothesis that the hops inhibit Gram‐positive lactic acid bacteria (S. bovis), and the rumen microbial community requires a period of adaptation before normal VFA production resumes. Selenomonas bovis and S. ruminantium both produce lactate, which is the substrate for propionate production by M. elsdenii. However, S. ruminantium has an outer membrane, while S. bovis does not. Significance and Impact of Study: The enhanced production of the gluconeogenesis precursor, propionic acid, provides further evidence that plant secondary metabolites from hops could be used to improve rumen fermentation.     

A simulation model “CTR Dairy” to predict the supply of nutrients in dairy cows managed under discontinuous feeding patterns

A simulation rumen model has been developed to function under non-steady state conditions in order to allow prediction of nutrient availability in dairy cows managed under discontinuous feeding systems. The model simulates availability of glycogenic, aminogenic and lipogenic nutrients to lactating dairy cows fed discontinuously. The model structure considers input of up to three different feeds fed independently at any time during the day. Feeds are described by their nitrogen (N), carbohydrate and fatty acid fractions. The N containing feed fractions include ruminally undegraded crude protein (CP), ruminally insoluble but potentially degradable CP, ruminally soluble CP and ammonia N. The feed carbohydrate fractions include ruminally undegradable neutral detergent fibre (NDF), ruminally degradable NDF, ruminally insoluble starch, ruminally soluble starch and sugars. The fatty acids in the feeds are divided between long chain fatty acids and volatile fatty acids (VFA). Additionally four pools were defined representing absorption of amino acids, glucose, long chain fatty acids and volatile fatty acids. The rumen microbial population is represented as a single pool. Besides a flexible structure, new features to the extant model include adoption of the concept of chewing efficiency (or chewing effectiveness) during eating, variable fractional ruminal absorption rates of VFA and variable fractional ruminal degradation rates of NDF as a function of rumen liquid pH, as well as a variable rumen volume which directly affects rumen concentrations of metabolites. The model continuously (i.e., by minute) predicts release of soluble components from the feeds in the rumen, concentration and absorption of fermentation end products in the rumen, rumen pools of nutrients and microbial biomass dynamics, as well as passage of microbial biomass and non-fermented nutrients from the rumen, in response to various feeding strategies. Model evaluation covered a wide range of feeding strategies that included pasture and housed feeding systems. Overall, the mean square prediction error (MSPE) as a percentage of the observed mean was relatively low (<10%) with a high amount of the total variation explained by random variation (>65%). Deviation from unity varied between 23% (rumen dry matter content) and 25% (NDF), indicating some consistent over and/or under prediction. A more detailed evaluation was done based on studies available that reported diurnal behaviour of key model outputs such as rumen pools, rumen pH, and rumen VFA. The predictions broadly simulated the observed values quantitatively, relative to general diurnal patterns, and relative to differences between treatments in the predicted diurnal patterns. Results show that the model provides a tool to assess potential outcomes of changing feeding strategies which may be particularly valuable in assessing selection of feeds, amounts and times of the day to offer the feeds. The continuous nature of the simulated output also allows determination of the time(s) of the day that ruminal (and/or post-ruminal) delivery of nutrients may limit ruminal output of nutrients (and/or availability of nutrients) to support milk nutrient synthesis.     

Surfactant-enhanced anaerobic acidogenesis of Canna indica L. by rumen cultures

Polyoxyethylene sorbitan monoolate (Tween 80) was used to enhance the anaerobic acidogenesis of Canna indica L. (canna) by rumen culture in this study. Dose of Tween 80 at 1 ml/l enhanced the volatile fatty acids (VFA) production from the acidogenesis of canna compared to the control. However, Tween 80 at higher dosages than 5 ml/l inhibited the rumen microbial activity and reduced the VFA yield. Response surface methodology was successfully used to optimize the VFA yield. A maximum of VFA yield of 0.147 g/g total solids (TS) added was obtained at canna and Tween 80 concentrations of 6.3g TS/l and 2.0 ml/l, respectively. Dosage of Tween 80 at 1-3.75 ml/l reduced the unproductive adsorption of microbes or enzymes on the lignin part in canna and increased microbial activity. A high VFA production was achieved from canna presoaked with Tween 80, suggesting that the structure of canna was disrupted by Tween 80.     

Volatile Fatty Acids and the Inhibition of Escherichia coli Growth by Rumen Fluid

Concentrations of volatile fatty acids (VFA) normally found in bovine rumen fluid inhibited growth of Escherichia coli in Antibiotic Medium 3. Acetic, propionic, and butyric acids each produced growth inhibition which was markedly pH-dependent. Little inhibition was observed at pH 7.0, and inhibition increased with decreasing pH. A combination of 60 mumoles of acetate, 20 mumoles of propionate, and 15 mumoles of butyrate per ml gave 96, 69, and 2% inhibition at pH 6.0, 6.5, and 7.0, respectively. Rumen fluid (50%) gave 89 and 48% inhibition at pH 6.0 and 6.5, respectively, and growth stimulation (22%) at pH 7.0. Rumen fluid inhibitory activity was heat-stable, was not precipitated by 63% ethyl alcohol, and was lost by dialysis and by treatment with anion-exchange resins but not with cation-exchange resins. These results are consistent with the idea that VFA are the inhibitory substances in rumen fluid. Previous results which indicated that rumen fluid VFA did not inhibit E. coli growth were due to lack of careful control of the final pH of the growth medium. The E. coli strain used does not grow in rumen fluid alone at pH 7.0.     

Comparison of Rumen Microbial Inhibition Resulting from Various Essential Oils Isolated from Relatively Unpalatable Plant Species

Essential oils were isolated from eight plant species which were relatively unpalatable to sheep and deer. The inhibitory potency of these essential oils upon sheep and deer rumen microorganisms was compared, in terms of total gas and volatile fatty acid (VFA) production, by use of an anaerobic manometric technique. Inhibitory effects of oils from the eight plant species may be placed in four groups: (i) essential oils from vinegar weed (Trichostema lanceoletum) and California bay (Umbellularia californica) inhibited rumen microbial activity most; (ii) lesser inhibition was exhibited by rosemary (Rosmarinus officinalis) and California mugwort (Artemisia douglasiana) oils, followed by (iii) blue-gum eucalyptus (Eucalyptus globulus) and sagebrush (Artemisia tridentata) oils; and (iv) oils from Douglas fir (Psuedotsuga menziesii) and Jerusalem oak (chenopodium botrys) resulted in the least inhibition, when 0.3 ml of each oil was used. A highly significant correlation coefficient (r = 0.98(**)) between total gas and VFA production indicated the validity of either method to measure the activity of rumen microorganisms. Our results are discussed in relation to the hypothesis that the selectivity and voluntary consumption of ruminants are related to the characteristic odor and antibacterial action of essential oils isolated from relatively unpalatable plant species.     

Effect of the level of dry matter and protein and degradation rate of starch on in vitro ruminal fermentation

Effects of starch type, feeding level and level of a mixed N source upon rumen fermentation were examined using an in vitro rumen simulation system (i.e., SIMCO) with a fluid volume of 1100 ml and liquid dilution rate of approximately 0.07/h. Two sources of starch, two feeding levels and two levels of N were examined in an experiment following a 2 × 2 × 2 factorial arrangement of treatments. The starch sources were raw slowly degrading (R), and cooked fast degrading (C), potato starch and constituted 450 g/kg diet dry matter (DM). The remaining was supplied in the form of a grass hay mixture. The feeding levels were 20 (DM20) and 40 (DM40) g DM/d and the diet N level was either low (N1) or high (N2), using peptone and ammonia salt additions in the buffer. Two simulations of 10 days each were completed. The amount of bicarbonate in buffer was varied according to feeding level, and pH (average 6.3) did not differ between treatments. An increased degradation rate of starch (R vs. C) depressed neutral detergent fibre (aNDFom) digestibility (0.46 vs. 0.36) and organic matter true digestibility (OMTD; 0.73 vs. 0.68), but there were no other treatment effects on digestibility. The VFA production efficiency (average 0.47 g VFA/g OMTD) was not affected by the main treatments, although an interaction between starch type and feeding level occurred. A decline in protozoa rating over the 10 day simulations was more apparent at the lower feeding level (DM20), indicating poor growth conditions for protozoa. Higher microbial efficiency (11.0 vs. 8.9 mg microbial N/g OMTD) and a higher proportion of propionate (272 vs. 207 mmol/mol VFA) occurred at DM20 compared to DM40. Increased degradation rate of starch (i.e., R vs. C) resulted in an improved microbial N efficiency (8.8 vs. 11.2 mg/g OMTD) and an increase in the proportion of propionate (226 vs. 253 mmol/mol VFA) at the expense of acetate (610 vs. 591 mmol/mol VFA). Increasing the level of N (i.e., N1 vs. N2) improved the microbial N efficiency (9.2 vs. 10.7 mg/g OMTD) and increased the proportion of propionate (230 vs. 249 mmol/mol VFA) and butyrate (100 vs. 119 mmol/mol VFA) at the expense of acetate (629 vs. 572 mmol/mol VFA). Interactions between starch type and N level upon VFA patterns were apparent. Results support earlier findings in that carbohydrate degradation rate is an important factor determining microbial growth rates and VFA distribution.     

Batch culture evaluation of carbohydrase inhibitors to moderate rumen fermentation

While carbohydrase inhibitors have been widely investigated for regulating human carbohydrate assimilation, their potential application to animal nutrition has been largely ignored. Batch culture fermentations were conducted to determine how commercially available α-amylase and α-glucosidase inhibitors affect rumen fermentation. Fermentations were with 0.5 g of ground corn grain, and 40 mL of buffered rumen fluid inoculum. Rumen fluid donors were fed a 0.5 concentrate 0.5 forage diet. Incubations were conducted in duplicate and replicated on consecutive days with pH and volatile fatty acid (VFA) concentrations measured. The microbial-derived inhibitors, acarbose (ACB) and trestatin (TRE), prevented the decreases in pH and VFA production observed in the control tubes at doses of 1.2–9.5 and 0.1–1.1 mg, respectively. Miglitol, glipizide, and the plant-derived amylase inhibitors failed to affect pH or reduce VFA concentrations with the same apparent potency as did ACB and TRE, which both show the potential to reduce the amount of starch fermented in the rumen. These compounds may be potentially useful for reducing ruminal acid production and allowing more starch to pass to the small intestine from the forestomachs.     

The functional significance of the browser-grazer dichotomy in African ruminants

The allometric relationships for the fermentation rate of dry matter, the total energy concentration of volatile fatty acids (VFAs), the energy supplied from VFA production and the mass of the digesta contents within the rumen or caecum and proximal colon (hindgut) were used to test whether the digestive strategies of grazing and browsing African ruminants differ. The wet and dry mass of the contents of the rumen and hindgut were allometrically related to body mass (BM). These relationships did not differ between browsing and grazing ruminants. The fermentation rates in the rumen were strongly allometric and the intercepts of the relationships did not differ between browsers and grazers. The fermentation rates in the hindgut were not allometrically related to BM and did not differ between ruminants with different feeding habits. Likewise, the total energy concentration of the VFAs in the rumen and hindgut showed no allometric scaling and did not differ between browsing and grazing ruminants. The energy supplied by VFA production in both the rumen and hindgut of African ruminants scaled at around 0.8 with BM. Only in the case of the energy supplied by VFAs in the rumen were there significantly different intercepts for browsing and grazing ruminants. The energy supplied by VFA production in the rumen was inadequate to meet the energy requirements for maintenance of browsers and small grazers. The retention time of digesta in the alimentary tract was positively related to BM although there was no difference in the allometric relationships for grazers and browsers. The results of these analyses suggest that, after controlling for the effects of body mass, there is little difference in digestive strategy between African ruminants with different morphological adaptations of the gut.