Modification of aflatoxin B1 and ochratoxin A toxicokinetics in rats administered a yeast cell wall preparation

The cell wall of Saccharomyces cerevisiae can bind mycotoxins in vitro, but there is scarce information on whether this property decreases the absorption of mycotoxins in vivo. The effect of a yeast cell wall preparation (YCW) on toxicokinetics and balance excretion (urine and faeces) of aflatoxin B(1) (AFB1) and ochratoxin A (OTA) was tested in rats after oral administration of each toxin. The (3)H-labelled mycotoxins were used at low doses. Co-administration of YCW with AFB1 decreased the extent, but not the rate, of absorption. Concurrently, radioactivity excreted in faeces increased by up to 55% when compared with controls, whilst the excretion in urine decreased (p < 0.05). The effect of YCW on OTA was less marked, although it increased radioactivity excretion in faeces (up to 16%; p < 0.05) it did not result in changes in urine and toxicokinetic parameters. The in vivo effect is in agreement with the reported in vitro binding ability for these toxins (AFB1 > OTA). In conclusion, these results indicate that YCW could be used to protect monogastric animals against exposure to low dietary levels of selected mycotoxins.

Methane output and diet digestibility in response to feeding dairy cows crude linseed, extruded linseed, or linseed oil

This experiment studied the effect of 3 forms of presentation of linseed fatty acids (FA) on methane output using the sulfur hexafluoride tracer technique, total tract digestibility, and performance of dairy cows. Eight multiparous lactating Holstein cows (initial milk yield 23.4 +/- 2.2 kg/d) were assigned to 4 dietary treatments in a replicated 4 x 4 Latin square design: a control diet (C) consisting of corn silage (59%), grass hay (6%), and concentrate (35%) and the same diet with crude linseed (CLS), extruded linseed (ELS), or linseed oil (LSO) at the same FA level (5.7% of dietary DM). Each experimental period lasted 4 wk. All the forms of linseed FA significantly decreased daily CH(4) emissions (P < 0.001) but to different extents (-12% with CLS, -38% with ELS, -64% with LSO) compared with C. The same ranking among diets was observed for CH(4) output expressed as a percentage of energy intake (P < 0.001) or in grams per kilogram of OM intake (P < 0.001). Methane production per unit of digested NDF was similar for C, CLS, and ELS but was less for LSO (138 vs. 68 g/kg of digested NDF, respectively; P < 0.001). Measured as grams per kilogram of milk or fat-corrected milk yield, methane emission was similar for C and CLS and was less for ELS and LSO (P < 0.001), LSO being less than ELS (P < 0.01). Total tract NDF digestibility was significantly less (P < 0.001) for the 3 supplemented diets than for C (-6.8% on average; P < 0.001). Starch digestibility was similar for all diets (mean 93.5%). Compared with C, DMI was not modified with CLS (P > 0.05) but was decreased with ELS and LSO (-3.1 and -5.1 kg/d, respectively; P < 0.001). Milk yield and milk fat content were similar for LSO and ELS but less than for C and CLS (19.9 vs. 22.3 kg/d and 33.8 vs. 43.2 g/kg, on average, respectively; P < 0.01 and P < 0.001). Linseed FA offer a promising dietary means to depress ruminal methanogenesis. The form of presentation of linseed FA greatly influences methane output from dairy cows. The negative effects of linseed on milk production will need to be overcome if it is to be considered as a methane mitigation agent. Optimal conditions for the utilization of linseed FA in ruminant diets need to be determined before recommending its use for the dairy industry.

Effect and stability of gliotoxin, an Aspergillus fumigatus toxin, on in vitro rumen fermentation

Aspergillus fumigatus is a toxicogenic fungus usually found in contaminated animal feeds, especially in conserved forages where it can produce several mycotoxins. Gliotoxin, one of the most important toxic metabolites produced by this fungus, has antibacterial, immunosuppressive and apoptotic effects. Ruminants due to the high proportion of forages they receive in the ration would be particularly exposed to gliotoxin. The objective of this work was (1) to assess the effect of gliotoxin on in vitro rumen fermentation and (2) to determine the effect of fermentation on gliotoxin stability. Gliotoxin did not affect rumen fermentation at concentrations found in naturally contaminated feeds. No effects were observed up to a concentration of 20 microg toxin ml(-1) and an extremely high toxin concentration (80 microg ml(-1)) was necessary to affect dry matter degradation, gas and total volatile fatty acids production by 24, 37 and 18%, respectively (p < 0.01). In addition, the toxin was unstable in the rumen environment with 90% disappearance at 6 h of incubation (p < 0.05). In contrast, extracts of A. fumigatus cultures containing gliotoxin at concentrations several times lower than that used for experiments with pure toxin had a negative effect on fermentations indicating the toxicity and possible synergism of other metabolites produced by this fungus. Extracts containing 8.8 microg gliotoxin ml(-1) decreased dry matter degradation, gas and volatile fatty acids production by 28, 46 and 35%, respectively (p < 0.01). Identification of these toxic metabolites and assessment of the rate of passage of gliotoxin to the lower intestinal tract is necessary to evaluate the potential risk of these toxins to ruminants.

Influence of pH on complexing of model beta-d-glucans with zearalenone

Previous studies have shown that isolated beta-(1,3 and 1,6)-D-glucans and related alkali-extracted fractions from the cell wall of Saccharomyces cerevisiae are able to complex with zearalenone in vitro (affinity up to 50%) and thus may reduce the bioavailability of toxins in the digestive tract. The complexation mechanisms involve cooperative interaction between the two chemical entities that can be computed by Hill's model. Various linear or branched soluble or insoluble beta-D-glucans were evaluated to elucidate their roles in the adsorption mechanisms under three pH conditions (3.0, 6.0, and 8.0) found in the digestive tract. A constant quantity of each beta-D-glucans (1 mg/ml) was mixed at 39 degrees C with increasing amounts of zearalenone (2 to 100 microg/ml), and the amount of bound toxin was measured. Acidic and neutral conditions gave the highest affinity rates (64 to 77%) by beta-(1,3)-D-glucans, whereas alkaline conditions decreased adsorption except when beta-(1,6)-D-glucan side chains were branched on beta-(1,3)-D-glucans. Alkaline conditions appear to impede the active three dimensional conformation of beta-D-glucans and favor single helix and/or random coil structures. Study of the equilibrium between beta-D-glucan-bound and free toxins revealed that two types of chemical interactions occur during toxin complexation with beta-D-glucans, identified as weak chemical linkages such as hydrogen and van der Waals bonds.

Adsorption of Zearalenone by beta-D-glucans in the Saccharomyces cerevisiae cell wall

Cell walls of yeasts and bacteria are able to complex with mycotoxins and limit their bioavailability in the digestive tract when these yeasts and bacteria are given as feed additives to animals. To identify the component(s) of the yeast cell wall and the chemical interaction(s) involved in complex formation with zearalenone, four strains of Saccharomyces cerevisiae differing in their cell wall glucan and mannan content were tested. Laboratory strains wt292, fks1, and mnn9 were compared with industrial S. cerevisiae strain sc1026. The complex-forming capacity of the yeast cell walls was determined in vitro by modelling the plots of amount of toxin bound versus amount of toxin added using Hill's model. A cooperative relationship between toxin and adsorbent was shown, and a correlation between the amount of beta-D-glucans in cell walls and complex-forming efficacy was revealed (R2 = 0.889). Cell walls of strains wt292 and mnn9, which have higher levels of beta-D-glucans, were able to complex larger amounts of zearalenone, with higher association constants and higher affinity rates than those of the fks1 and sc1026 strains. The high chitin content in strains mnn9 and fks1 increased the alkali insolubility of beta-D-glucans from isolated cell walls and decreased the flexibility of these cell walls, which restricted access of zearalenone to the chemical sites of the beta-D-glucans involved in complex formation. The strains with high chitin content thus had a lower complex-forming capacity than expected based on their beta-D-glucans content. Cooperativity and the three-dimensional structure of beta-D-glucans indicate that weak noncovalent bonds are involved in the complex-forming mechanisms associated with zearalenone. The chemical interactions between beta-D-glucans and zearalenone are therefore more of an adsorption type than a binding type.

Two-step freezing procedure for cryopreservation of rumen ciliates, an effective tool for creation of a frozen rumen protozoa bank

The present study aimed at the long-term storage of rumen protozoa as living cells in liquid nitrogen. The two-step or interrupted slow freezing procedure was used to cryopreserve six of the dominant species of rumen ciliates isolated from monofaunated animals, Dasytricha ruminantium, Entodinium caudatum, Epidinium ecaudatum caudatum, Eudiplodinium maggii, Isotricha prostoma, and Polyplastron multivesiculatum. We optimized the first step in the interrupted slow freezing procedure, from the extracellular ice nucleation temperature to the holding temperature, and studied the effects of the cooling rates on survival. In addition to the nature of the cryoprotectant (dimethyl sulfoxide), the equilibration temperature and equilibration time (25 degrees C and 5 min, respectively), and the holding time at subzero temperature (45 min) recommended previously (S. Kisidayová, J. Microbiol. Methods 22:185-192, 1995), we found that a holding temperature of -30 degrees C, a cooling rate from extracellular ice nucleation temperature to holding temperature of between 1.2 degrees C/min and 2.5 degrees C/min, depending on the ciliate, and rumen juice as the freezing and thawing medium markedly improved the survival rate. Survival rates determined after 2 weeks in liquid nitrogen were 100% for Isotricha, 98% for Dasytricha, 85% for Epidinium, 79% for Polyplastron, 63% for Eudiplodinium, and 60% for Entodinium. They were not significantly modified after a period of 1 year in liquid nitrogen. Four of the five ciliate species cryopreserved for 8 months in liquid nitrogen successfully colonized the rumen when inoculated into defaunated animals. These results have made it possible to set up a bank of cryopreserved rumen protozoa.

A xylanase produced by the rumen anaerobic protozoan Polyplastron multivesiculatum shows close sequence similarity to family 11 xylanases from gram-positive bacteria

We report for the first time the cloning and characterisation of a protozoal enzyme involved in plant cell wall polysaccharide degradation. A cDNA library was constructed from the ruminal protozoan Polyplastron multivesiculatum and a stable clone expressing xylanase activity was isolated. The encoded enzyme belongs to the glycoside hydrolase family 11, and phylogenetic analysis indicates a closer relationship with catalytic domains from Gram-positive bacteria than the other fibrolytic eukaryotes from the rumen, the anaerobic fungi.

Effect of a Saccharomyces cerevisiae culture on nutrient digestion in lactating dairy cows

The digestive effects of a Saccharomyces cerevisiae culture were investigated. Four cows in early lactation that were fitted with ruminal and duodenal cannulas were used in a crossover design. The diet, which consisted of 60% corn silage and 40% concentrates, was supplemented or not supplemented with a daily dose of 50 g of premix containing 0.5 g of S. cerevisiae (6 x 10(8) cfu/g of premix). Total and ruminal digestibilities of organic matter, duodenal flows of nonmicrobial and microbial N, solid and liquid turnover rates, ruminal protozoal numbers, pH, ammonia N and volatile fatty acid concentrations, and concentrations of some plasma metabolites were not modified by the addition of S. cerevisiae. Ruminal dry matter content increased when S. cerevisiae was supplemented to the diet. In situ ruminal degradabilities of dry matter and neutral detergent fiber from corn stalk and of N from soybean meal were not modified; degradability of acid detergent fiber from corn stalk increased (32.5% vs. 26.3%) with the addition of S. cerevisiae. A short-term increase in N degradation was observed after 4 and 8 h of incubation. This experiment showed no effect of S. cerevisiae on most quantitative digestive events; however, a positive transitory postprandial effect on some parameters of microbial activity was observed.

The effect of Saccharomyces cerevisiae and Aspergillus oryzae on the digestion of the cell wall fraction of a mixed diet in defaunated and refaunated sheep rumen

The objective of this study was to determine the effect of two probiotics, Saccharomyces cerevisiae (SC) and Aspergillus oryzae (AO), without their culture medium, on the digestion of plant cell wall components in sheep that had been successively defaunated and refaunated. Six sheep fitted with large rumen cannulae were used to study 1) defaunated sheep with no probiotic, 2) defaunated sheep with SC or AO, 3) refaunated sheep with no probiotic, 4) refaunated sheep with SC or AO. The apparent digestibility of the plant cell walls was not altered (P > 0.05) by the probiotics in defaunated sheep but was increased (P < 0.05) with SC (+16%) in refaunated sheep. Simultaneously, SC stimulated the growth of the protozoal population in the rumen. As noted in most previous experiments, the positive effect of the presence of protozoa on plant cell wall digestion (P < 0.001) was confirmed here. The effect (P > 0.05) of SC or AO on in situ ADF digestion was either not significant or negative in defaunated rumens, whereas it became positive in refaunated rumen after a residence time of 12 h. The improvement of in situ ADF digestion due to the presence of protozoa was significant (P < 0.05 for NDF; P < 0.001 for ADF). However, we could not determine whether this was a direct effect of protozoa or an indirect effect operating via bacteria. The limits of the nylon bag technique for evaluating the microbial activity are discussed in relation to the ability of protozoa to enter and grow in the bags, and the pH regulation inside the bags. The pH values below 5.5 noted inside the bags can significantly alter the bacterial and protozoal populations and limit the validity of the technique. SC increased (P < 0.05) the specific activity of CMCase and xylanase of the solid-adherent bacteria (SAB) isolated from the rumen digesta of refaunated sheep. Stimulation of both the bacterial activity and protozoa numbers could explain the positive effect of SC on cell wall digestion in the rumen since the modelling of marker excretion in faeces showed that the ruminal mean retention time of hay measured from the model of Danhoa et al. was not modified (P > 0.05) by either refaunation or the presence of probiotics. AO increased (P < 0.05) the total retention time of the solid particles in the whole digestive tract and increased the ruminal liquid volume in the refaunated animals but it had no effect on the protozoa population or on the polysaccharidase activity of the SAB, which could explain the absence of effect of AO on the total digestibility of plant cell walls. Both probiotics decreased the liquid turnover in defaunated rumens (P < 0.05) but neither had any effect (P > 0.05) on this parameter after refaunation. The improvement of plant cell wall degradation in the whole digestive tract is probably due to a stimulation of digestion at the rumen level as indicated by the higher activity of the SAB in rumen digesta and the growth of protozoa.

The role of ciliate protozoa in the lysis of methanogenic archaea in rumen fluid

Predation by ciliate protozoa can account for 90% of the eubacterial protein turnover in the rumen. However, little is known about the factors affecting the lysis of archaea in rumen fluid. Bacterial lysis was followed from the release of acid-soluble 14C from 14C leucine-labelled bacteria. The rumen methanogen Methanobrevibacter MF1 was broken down more rapidly than other non-ruminal archaea in rumen fluid withdrawn from sheep harbouring either a mixed protozoa population or monofaunated with Polyplastron multivesiculatum or Entodinium spp. The removal of protozoa from the rumen fluid had little effect on the breakdown of Methanobrevibacter, while lysis of the non-methanogenic ruminal bacterium Selenomonas ruminantium decreased by over 70%. Substantial lysis of Methanobrevibacter occurred in cell-free rumen fluid and this effect could be abolished by autoclaving. In view of the high number of bacteriophages in rumen fluid and susceptibility of ruminal bacteria to phage-induced lysis it is tempting to suggest that phages have a role in the lysis of archaea in rumen fluid.

Methane production associated with rumen-ciliated protozoa and its effect on protozoan activity

Methane production by methanogenic bacteria associated with ciliated protozoa in the rumen, and its effect on the metabolic activity of the protozoa, were measured in vitro. Apparent daily methane emission per protozoan cell ranged from a trace amount to 2 nmol. Enhanced substrate disappearance accompanIed methanogenesis.

Effect of rumen protozoa on nitrogen utilization by ruminants

Results obtained during the past decade indicate clearly that protozoa are actively involved in the degradation of dietary and microbial proteins in the rumen. Because of the great ability of protozoa to ingest the particulate matter suspended in the rumen, protozoa are more active in degrading insoluble than soluble proteins. This indicates that studies carried out using lysed and sonicated protozoa are not appropriate for quantifying the actual contribution of protozoa to protein degradation in the rumen. In vivo trials have confirmed that duodenal flow of both undegraded dietary protein plus bacterial protein generally is increased by defaunation. The decrease in ruminal ammonia concentration consistently observed after defaunation accounts for the lower urinary nitrogen (N) excretion found in defaunated animals, whereas the increase in fecal N excretion in the same animals probably results from a shift of plant cell wall digestion from the rumen to the large intestine. Total N excretion is not altered significantly by defaunation. A summary of literature data indicates there are contradictory effects of defaunation on ruminant performance. This implies that animal response to defaunation may depend on the specific nutrient-limiting performance on the one hand and on the modifications of digestion and metabolism resulting from defaunation on the other. Different methods are proposed to either eliminate or decrease the numbers of ruminal protozoa or to alter their makeup. However, none of these approaches has been tested under practical feeding conditions.

The effect of Saccharomyces cerevisiae and Aspergillus oryzae on fermentations in the rumen of faunated and defaunated sheep; protozoal and probiotic interactions

We measured the effect of the direct addition to the rumen of Saccharomyces cerevisiae (SC 50 mg/day) and Aspergillus oryzae (AO 3 g/day) on the fermentation processes in fistulated sheep. The measurements were carried out on animals whose rumens were first defaunated and then refaunated. The animals received a ration composed of hay (600 g/day), barley (600 g/day) and soybean meal (150 g/day), fed twice daily in two equal meals. The number of fungi and total, viable or cellulolytic bacteria were lower after the inoculation of protozoa in defaunated rumens. The probiotics stimulated the development of total bacteria but reduced the population of cellulolytic bacteria. The addition of the probiotics and the presence of protozoa each incurred a decrease in the redox potential values. The association of both treatments had an additive effect on this parameter. The two probiotics and the protozoa stabilized the rumen pH after the meal, maintaining it above the value of 6 for a longer period of time. The positive effects on pH were accumulated in the refaunated animals receiving probiotics. The ammonia nitrogen concentration was considerably increased by the presence of the protozoa; the probiotics increased the ammonia concentration only in the refaunated sheep. The methane and hydrogen proportions in the fermentation gases were invariably higher in the refaunated animals. The probiotics had no clear effect either on the gas composition or the concentration and the composition of the mixture of volatile fatty acids; only the concentration of isovalerate was significantly increased by probiotics and only in refaunated animals. The protozoa did, however, considerably increase the concentrations of acetate, butyrate and isoacids and decreased the concentration of caproate.

The importance of methanogens associated with ciliate protozoa in ruminal methane production in vitro

The importance of methanogenic bacteria associated with ciliate protozoa was estimated either by removing protozoa from whole rumen fluid (using defaunated rumen fluid to correct for the effects of centrifugation on bacteria) or by isolating the protozoa. Rumen fluid was withdrawn from sheep inoculated with either Polyplastron multivesiculatum, a co-culture of Isotricha prostoma plus Entodinium spp. or a mixed type B fauna of Entodinium, Eudiplodinium and Epidinium spp. Methanogenesis was highest in rumen fluid containing a mixed protozoal population of the following genera: Entodinium, Eudiplodinium and Epidinium, was lower in defaunated rumen fluid and lowest in rumen fluid containing either I. prostoma plus Entodinium or P. multivesiculatum. Methanogenic bacteria associated with rumen ciliates were apparently responsible for between 9 and 25% of methanogenesis in rumen fluid.

Influence of lasalocid, cationomycin and feeding frequency on the postprandial kinetics of some plasma parameters in the rumen vein, portal vein and mesenteric artery of sheep

Two adult sheep, A and B, received successively during three experimental periods a forage-based pelleted feed, then the same diet supplemented with 33 mg/kg of lasalocid (L) or cationomycin (C). The feed was given in either eight (sheep A) or two (sheep B) daily meals. After four weeks of adaptation, 11 blood samples were taken through catheters in the rumen vein (RVA) and the mesenteric artery (MAA) in sheep A and in the rumen vein (RVB) and portal vein (PVB) in sheep B over a 5-hour period after the morning meal. Because of a blockage in the catheter it was not possible to measure the effect of C in MAA. Food intake had no immediate effect on the plasma levels measured: the distribution of eight daily meals stabilized plasma levels and made it easier to determine the effect of the ionophores. This effect varied according to the sampling site, the animal and the antibiotic, sometimes contradictorily. All the plasma parameters monitored in RVA were significantly modified by either one of the ionophores. A decrease in plasma albumin concentration (P < 0.05) was observed with L in MAA and with C in RVA and MAA. Aceto-acetate concentration decreased (P < 0.05) with L in MAA but increased with L and C in RVB. A decrease in glycaemia and uraemia (P < 0.05) was observed with L in MAA, RVA and RVB and with C in RVA. Total amino acid concentration decreased (P < 0.05) with C in RVA or increased (P < 0.05) with L in PVB and RVB. These variations in results may be due to different mechanisms of action of L and C on digestion, particularly in the rumen. While the changes undergone by the ketone bodies in the blood suggested a decrease in hepatic ketogenesis with L, there was no evidence that the ionophores had a direct postprandial effect.

Reassessing the manipulation of protein synthesis by rumen microbes

Protein synthesis by rumen microbes plays an important role in ruminant nutrition. Microbial proteins that are not recycled flow out of the rumen and account for more than 50% of the total proteins entering the intestines. Determination of microbial nitrogen in digesta is based on the isolation of a representative sample of rumen microbes and on the use of specific markers (purine bases, RNA, 15N incorporation). This review discusses the reliability of microbial markers and examines current methods for assessing differences in turnover rate and microbial composition among liquid and particulate compartments. Four groups of factors acting on microbial synthesis, which are also adaptable to farm conditions, are considered: I) modification of protozoal population; II) modification of liquid and solid phase kinetics in the rumen; III) balance in the components of the diet; and IV) probiotics. The effects of these factors are discussed, considering their feasibility and their usefulness for the host.

Effect of ruminal inoculation of Isotricha alone or a mixed B-type fauna in a defaunated rumen on the digestion of a hay-maize diet (70:30) in sheep

Two adult sheep (75 kg live weight) fitted with rumen cannulas were defaunated by the emptying method during the first period of the experiment. They were inoculated with the genus Isotricha alone during the second period, and with a mixed ciliate population (Entodinium, Eudiplodinium, Epidinium) during the third. They were fed a diet of grass hay (840 g) and pelleted maize grains (360 g) in 8 meals per day, every 3 h. Defaunation was successful and no accidental contamination occurred during the experiment. The protozoa had no significant effect on the volume of rumen digesta, nor on the turnover of the particulate phase. The addition of Isotricha and of the mixed fauna increased the ADF digestibility of the diet but, in the same animals, lowered the in sacco degradation of wheat straw. The ruminal pool sizes of dry matter (DM), organic matter (OM), nitrogen (N), neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid lignin detergent (ADL) remained unchanged after protozoa inoculations. The concentration of total volatile fatty acids (VFA) was not altered by faunation with Isotricha or a mixed fauna. The molar proportion of acetate increased at the expense of all the other VFAs (mainly propionate with the mixed fauna). Correspondingly, the proportion of methane in the rumen gases increased and that of CO2 decreased in inoculated animals. The ammonia concentration was highest in animals with a mixed fauna and lowest in those inoculated with Isotricha alone. This trend is explained in terms of the specific effect of the different genera of protozoa on nitrogen metabolism.

Digestion of a dehydrated lucerne/barley diet (70:30) in defaunated, Isotricha-monoinoculated and mixed-fauna-inoculated rumen in sheep

Two adult Texel sheep fitted with permanent rumen fistulae were defaunated for 12 weeks in a preliminary experiment. They were then reinoculated with Isotricha sp for 11 weeks, and finally with a mixed fauna (Entodinium, Epidinium, Eudiplodinium and Isotricha) for 10 weeks. They were fed a diet composed of dehydrated lucerne (700 g/d), pelleted barley grain (300 g/d), grass hay (100 g/d) and wheat straw (50 g/d) in one daily meal. Isotricha and the ciliates of the mixed fauna developed rapidly, reaching a maximum concentration 9-17 d after inoculation. Their concentration then fell for 2-3 d and finally stabilized at values close to 10(4)/ml for Isotricha, Eudiplodinium and Epidinium and 2.5 x 10(5)/ml for Entodinium. The estimated ciliate biomass in the rumen was 1.8 g l-1 for a volume of 10.2 ml l-1 in the Isotricha-monoinoculated sheep and 4.7 g l-1 for a volume of 25.0 ml l-1 in mixed-fauna-inoculated sheep. The concentration of Isotricha was unaffected by the inoculation of mixed fauna during the third part of the experiment. No difference in total rumen bacteria counts was observed between defaunated, monoinoculated and completely refaunated animals. The total adenylic nucleotide concentration in filtered rumen juice was 4 times higher in faunated sheep just before feeding and 4-9 times lower after feed intake as compared to defaunated animals; the energy charge was always higher in faunated animals. These results are discussed in relation to the digestive activity and biomass of the protozoa. The in situ degradation of lucerne stems was the highest in the mixed-faunated sheep over a retention time interval of 6-18 h. The values obtained in Isotricha-monoinoculated sheep were intermediate between the defaunated and the mixed-faunated states. The digestibility in the whole digestive tract of dietary dry matter, organic matter, nitrogen and neutral detergent fibre was unaffected by the addition of either Isotricha or the mixed fauna in defaunated rumens. The total volatile fatty acid concentration was higher (p < 0.05) in the defaunated sheep between 6 and 18 h after feeding. The molar proportion of butyrate was significantly (p < 0.05) increased by the presence of mixed fauna in the rumen while that of propionate and valerate was lower. A non-significant decrease in acetate was also observed. The concentration of NH3-N in the rumen was significantly increased (p < 0.05) by the presence of the mixed fauna in the rumen but was unaffected or slightly reduced by Isotricha alone.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of lasalocid and cationomycin on the evolution of certain parameters in the blood plasma of sheep

Six adult sheep were fed at maintenance level, successively over three experimental periods, 1100 g of a roughage-rich diet without supplement or containing 33 mg kg-1 of lasalocid or cationomycin. The feed was administered in eight equal meals daily, every three hours. Blood samples were taken in each animal from the jugular vein at 10.00 hours, 16.00 and 22.00 hours, one hour after the animals were fed. The ionophores did not affect the plasma concentrations of glucose, free fatty acids, total amino acids, insulin, acetate, Ca or Mg. They decreased beta-hydroxy butyrate content (P < 0.05) and increased that of albumin (P < 0.05). Lasalocid alone significantly decreased uremia, but the significant threshold was only reached at 16.00 hours (P < 0.01). With this exception, the two ionophores had similar effects. Samples taken in peripheral blood appear to be too far from nutrient absorption sites to give a clear indication of the effects of these molecules on the products absorbed or metabolised in the digestive tract.

Manipulation of microbial activity in the rumen

Different methods of optimizing feed conversion into nutrients in the rumen are now available to scientists. But the rumen must be considered as an integrated system and this makes it difficult to rationalize manipulation. The observed result of any treatment is a combination of several interactive reactions. Any change to one component of the system has several uncontrolled effects on other components. The positive effects aimed for are sometimes associated with undesirable effects. Numerous chemical additives have been studied during the last two decades among which ionophore antibiotics represent the most important group. The interest of non-ionophore antibiotics, methane inhibitors, and compounds inhibiting proteases or deaminases, has also been considered during the last years. The observed effects of these chemical additives on animals, and their possible mode of action on rumen microbes and on animal metabolism, are discussed. However, the risks of the presence of residues in meat and milk are questioned by consumers. Microbial activity in the rumen can be altered by feeding animals with large amounts of certain food constituents (fats, starch) or minerals (buffer substances). The responses in the rumen to these dietary conditions are analyzed in terms of the digestive effects on plant cell wall degradation and microbial protein synthesis. Modification of the rumen microbial population is now considered as a possible approach to rumen manipulation by scientists. The effects on digestion of the elimination of ciliate protozoa (defaunation) are presented. The feasibility of these objectives, from a practical standpoint, is discussed. Finally, there is an overview of the effects of the addition of live yeasts (Saccharomyces cerevisciae), or fungi (Aspergillus orizae), used as probiotics. A possible mode of action of probiotics on the rumen ecosystem is suggested.

Effects of Isotricha, Eudiplodinium, Epidinium + Entodinium and a mixed population of rumen protozoa on the in vitro degradation of fish meal, soybean meal and casein

An in vitro rumen simulation system was used to study effects of different types of rumen protozoa (Isotricha, Eudiplodinium, Epidinium + Entodinium, total mixed fauna) on the degradation of three feed proteins (fish meal, soybean meal, casein). A comparison of the fermentations containing different feed proteins was made with the control fermentations containing no added feed protein. Rumen contents used in the fermentations originated from defaunated sheep, or from sheep containing a single genus of protozoa (Isotricha spp. or Eudiplodinium spp.), a mixture of genera Entodinium spp. and Epidinium spp., or a total mixed fauna. In the presence of the total mixed fauna the degradabilities were 82.0, 51.1 and 26.5% for casein, soybean meal and fish meal, respectively. The absence of protozoa resulted in decreased (P < 0.05) degradation of fish meal and soybean meal but had no effect (P > 0.05) on casein. The single genus Isotricha spp. decreased (P < 0.05) the degradation of all three protein sources compared with the defaunated fermentations or those containing the total mixed fauna. Eudiplodinium did not affect (P > 0.05) fish meal or soybean meal, but it decreased (P < 0.05) the degradation of casein compared with the defaunated fermentations. However, when this organism was compared with the total mixed fauna the degradability of fish meal was not affected (P > 0.05), but that of soybean meal or casein was decreased (P < 0.05). The combination of Epidinium + Entodinium decreased (P < 0.05) the degradation of all three protein sources when compared with the total mixed fauna. When compared with the defaunated fermentations, the protozoal combination had no effect on fish meal (P > 0.05), but the degradation of soybean meal and casein was decreased (P < 0.05). Total volatile fatty acid (VFA) production was systematically reduced (P < 0.05) by the sole presence of Isotricha. The presence of other genera or the total mixed fauna had variable effects on the production of VFA or gases for different sources of protein. It was concluded that the mode of action of a single species or genus of protozoa on nitrogen metabolism in the rumen is different from that of total mixed fauna. The protozoal effect on protein degradation varies according to the type of protozoa present and the nature of the protein. Key words: Protozoa, in vitro degradation, fish meal, soybean meal, casein, rumen

Comparative effects of feeding and duodenal infusion of monensin on digestion in sheep

The effect of monensin on digestion was compared when it was used as feed additive or infused into the duodenum. Six Texel wethers fitted with ruminal, simple duodenal and re-entrant ileal cannulae, divided into three groups, were fed a mixed diet alone (control) or with 33 mg of monensin in feed or infused through the duodenal cannula. The experiment was designed as a 3 × 3 Latin square. Feeding monensin increased (P < 0.05) the amount of OM digested in the rumen and small intestine; infusion into the duodenum had no effect on this parameter. Monensin had no effect on the extent or site of N digestion. No ruminal recycling of monensin was observed since ruminal VFAs were not altered by monensin infusion into the duodenum. VFAs in the hindgut were only modified when monensin was fed (improvement of propionate proportion, P < 0.05). Amylase activity remained unchanged in the intestine whatever the monensin supply. Only fed monensin increased (P < 0.05) trypsin activity. Infused monensin increased the plasma glucose level (P < 0.05), which indicates that monensin has metabolic effects. These results show that the intestine is not the major target for monensin when it is used as a growth promoter in ruminants. Key words: Monensin, intestinal digestion, plasma glucose, sheep, VFA, nigrogen

Effects of lasalocid and cationomycin on the digestion of plant cell walls in sheep

The effect of lasalocid and cationomycin on plant cell wall digestion was tested in a Latin square design experiment over three periods on six adult sheep fed three diets: a control diet (T) without antibiotics, a diet (L) with 33 mg kg−1 of lasalocid, and a diet (C) with 33 mg kg−1 of cationomycin. The dry matter and plant cell wall digestibilities were not affected by the addition of antibiotics. The digestive flow measurements at the duodenum showed that the antibiotic had no effect on the apparent digestion of dry matter, organic matter and plant cell walls along the digestive tract. This was confirmed by the in sacco feed and pure cellulose rumen degradation measurements. Lasalocid, however, decreased the true digestion of feed dry matter in the rumen, as shown by the duodenal flow measurements after being corrected for microbial dry matter. Compared with the control diet, diets (L) and (C) increased the propionate percentage in the rumen VFA mixture (T = 14.9, L = 19.4, C = 18.9) and decreased acetate (T = 66.1, L = 63.8, C = 65.7) and butyrate (T = 14.1, L = 12.7, C = 11.7) percentages. The addition of antibiotics decreased the rumen ammonia nitrogen concentration by 14%. The CO2 to CH4 ratio in the gas mixture was, however, not statistically modified, and no ionophore effect was observed on the protozoa mean population. Key words: Lasalocid, cationomycin, digestion, cell wall carbohydrates, sheep, rumen

The influence of lasalocid and cationomycin on nitrogen digestion in sheep: Comparison of methods for estimating microbial nitrogen

An in vivo study was carried out to evaluate the effect of a new ionophore (cationomycin) on nitrogen digestion compared with lasalocid. Three diets based on forage were given (a control diet, a "cationomycin" diet, a "lasalocid" diet) to six sheep fitted with rumen duodenal and ileal cannulae over three different periods in a Latin square design experiment. The supply of lasalocid or cationomycin (33 mg kg−1) decreased (P < 0.05) the breakdown of dietary proteins in the rumen and lowered the microbial protein synthesis whatever the microbial marker used (diaminopimelic acid or purine bases). The duodenal and ileal flows of organic matter (OM), ammonia nitrogen (NH3-N), nonammonia nitrogen, and amino acids (AA) were not affected by the ionophore addition. We could not use the AA profile method to estimate the microbial contribution to the duodenal flow of nonammonia nitrogen because of the strong similarities in AA composition of the feed and the rumen microbial sample. The efficiency of microbial synthesis was significantly (P < 0.05) decreased by cationomycin, and tended to decrease with lasalocid. Only lasalocid increased the digestibility of dietary nitrogen in all the digestive tract. Key words: Ionophore, lasalocid, cationomycin, digestion, nitrogen, sheep, rumen

Use of a semicontinuous culture system (RUSITEC) to study the metabolism of ethanol in the rumen and its effects on ruminal digestion

The metabolism of ethanol by rumen micro-organisms and its effects on rumen fermentations have been studied in vitro in a semicontinuous fermentor (RUSITEC). Ethanol introduced in the fermentor at 1, 4 or 8 g d−1 L−1 of rumen juice induced important qualitative and quantitative modifications in the fermentation outputs. Total VFA production was increased from 5 to 40% according to the diet and ethanol concentration. Relative proportions of VFA were modified: caproate concentration increased three times, propionate and isovalerate concentrations decreased significantly in most cases. Methane production was increased. Whatever the ethanol concentration and the type of diet, in vitro digestibility parameters and end-products from solid feedstuffs stayed practically unchanged by ethanol addition. Except with the lowest supply (1 g d−1 L−1), ethanol induced an uncoupling effect on the metabolism of rumen bacteria and decreased biomass production. Radioactivity of 2-14C ethanol was recovered mainly in acetate (77–80%). Microbial transformation of ethanol in RUSITEC was limited regardless of ethanol concentration. Ethanol had a negligible effect on the digestibility of solid feedstuffs but induced consistent qualitative changes in rumen fermentations. Key word: Ethanol, metabolism, rumen, semicontinuous culture

Development of the rumen digestive functions in lambs placed in a sterile isolator a few days after birth

The development of the rumen digestive functions was studied in lambs placed in sterile isolators at 1, 4, 8 or 9 days of age to define the role of the bacterial species that colonize the rumen just after birth. The values of the main rumen digestive parameters (pH, concentrations of volatile fatty acid, ammonia, lactic acid) in these lambs were close to those observed in conventional controls. Likewise, the digestive utilisation of the dry matter and starch was comparable in isolated and control animals but the digestibility of crude cellulose was higher in isolated lambs, which harboured only Fibrobacter succinogenes as the sole cellulolytic bacterial species. These results suggest that the rumen flora of the very young lamb play an essential role in the establishment of the rumen ecosystem and in the setting up of the digestive functions.

The influence of physiological state and dietary nitrogen supply on digestion in the dairy cow

The effects of N supply on digestion were compared in cows in late pregnancy vs early lactation. Two groups of four and one group of three dairy cows received, during a digestion trial, corn silage-concentrate diets (65:35) differing in N supply. Concentrates were formulated so that diets were either insufficient (Diet 1) or sufficient (Diets 2 and 3) in ruminally fermented N and either insufficient (Diets 1 and 2) or sufficient (Diet 3) in protein digestible in the intestines. Experimental periods were 3 wk before and 3 wk after parturition. Organic matter digestibilities were 69.8, 73.1 and 72.5% in late pregnancy vs 64.9, 69.8 and 70.8% in early lactation for Diets 1, 2 and 3, respectively. Digestibility was higher (P less than .05) in late pregnancy than in early lactation. Differences between physiological states were attributed to differences in ruminal digestibility and in fiber digestibility. These differences were not explained by a reduction in large particle retention time, but in situ DM disappearance was reduced in early lactation. Ruminal protozoa concentration and the acetate: propionate ratio decreased between pregnancy and lactation. The duodenal non-ammonia N:N intake ratio was higher for Diet 1 than for Diets 2 and 3, 1.20, .97 and .94, respectively, but it did not vary between physiological states. In conclusion, some of the negative consequences of a shortage in degraded N are more dramatic in early lactation than in late pregnancy.

Effect of defaunation on protein and fibre digestion in sheep fed on ammonia-treated straw-based diets with or without maize

Using a defaunating method which preserved bacteria and fungi in the rumen, the effect of protozoa on protein and fibre digestion was studied in six adult wethers in relation to the nature of the diet. Sheep were given daily, 42 g dry matter (DM)/kg metabolic body-weight (W0.75), one of two isonitrogenous diets: one contained ammonia-treated wheat straw as the only energy source (diet S) and the other was supplemented with maize grain pellets (diet SM). Mean daily intakes (g/d) of nitrogen, neutral-detergent fibre and acid-detergent fibre were respectively 22, 573 and 373 for diet S and 23, 450 and 334 for diet SM. Elimination of protozoa increased duodenal non-ammonia-nitrogen flow. This result was mainly due to an increase in microbial protein flow and, to a lesser extent, to a higher dietary protein flow. Defaunation markedly increased the efficiency of microbial protein synthesis. Maize-grain supplementation had a net positive effect on this variable in defaunated sheep, but not in faunated sheep. Cell-wall carbohydrates were less well digested in the defaunated rumen, and the negative effect of defaunation was greatest with the diet SM. Intestinal fibre digestion increased in the defaunated sheep especially in those fed on diet SM, but not enough to compensate for the decrease in rumen digestion.

In vitro study (Rusitec) of the action of abierixin, a new ionophore antibiotic, on the end products of fermentation and the degradation of nitrogen in the rumen

We investigated the capacity of a new ionophore antibiotic, abierixin, to modify fermentations in the rumen using a semi-continuous fermenter (Rusitec). As in the studies carried out on a "batch" fermenter (HILLAIRE et al., 1989a), abierixin failed to alter volatile fatty acids and gas productions but, in contrast, it limited the degradation of dietary nitrogen without affecting microbial synthesis. This molecule which has a low level of toxicity and is capable of improving the use of dietary proteins by ruminants, was found to be more effective when used at very low dose levels.

In vitro study of the effect of different ionophore antibiotics and of certain derivatives on rumen fermentation and on protein nitrogen degradation

An in vitro study was carried out to evaluate the effect of different ionophore antibiotics and some of their derivatives on rumen fermentation and on the degradation of peanut meal nitrogen. The increase in the production of propionic acid at the expense of acetic acid, observed with lonomycin, nigericin, cationomycin and lysocellin, was identical to that noted with monensin. The decrease in methanogenesis observed in the presence of monensin was also found with cationomycin and lysocellin. With the exception of lysocellin, which greatly reduced protein degradation of peanut meal, and of nigericin, which had no effect on this parameter, the 2 other molecules presented the same action as monensin. The negative effect of monensin on microbial ammonia uptake was demonstrated with the same intensity in the presence of cationomycin; it was slightly higher with nigericin and particularly accentuated with lonomycin and lysocellin. Three ester derivatives of monensin (monensin acetate, monensin propionate and monensin butyrate) had a similar action to that of monensin on the orientation of rumen fermentations. The monensin isobutyrate derivative appeared to be more active than monensin and only weakly altered microbial ammonia uptake. The oxolonomycin and hydroxolonomycin derivatives behaved identically to lonomycin with respect to microbial metabolism and protein nitrogen degradation. Unlike the molecules from which they derive, the deacylated cationomycin and nigericic acid had no effect on the orientation of rumen fermentations. Of the compounds tested and presenting a potential 'growth-promoting action' at least comparable to that of monensin, and which demonstrated lower toxicity on mice, three molecules (oxolonomycin, lysocellin and cationomycin) appeared to present a zootechnical interest as feed additives for growing cattle.

Establishment of Bacteroides succinogenes and measurement of the main digestive parameters in the rumen of gnotoxenic lambs

We attempted to determine the degree of diversification of the microflora that allow the establishment of Bacteroides succinogenes S85 in the rumen of gnotoxenic lambs. Four lambs (group I) received an inoculum orally, composed of 182 noncellulolytic bacterial strains (inoculum 1) previously isolated from the rumen of conventional young lambs. Two lambs (group II) were inoculated with 32 strains (inoculum 2) selected among the 182 strains of inoculum 1. Two lambs (group III) received an inoculum (inoculum 3) composed of 106 noncellulolytic bacterial strains previously isolated from the rumen of meroxenic lambs. Two lambs (group IV) were inoculated with 16 strains (inoculum 4) chosen among the 106 strains of inoculum 3. All lambs were inoculated from birth except two lambs of group I, which were inoculated from 1 month of age. Each lamb then received orally a pure culture of B. succinogenes. This strain became established more easily in the rumen of lambs that had received complex inocula (group I). Its population reached a level close to that generally observed in conventional lambs (10(7)-10(8) bacteria.mL-1). In contrast, B. succinogenes became established in only one lamb of group II, but bacterial numbers varied considerably. In group III, repeated inoculations were necessary to obtain its definitive establishment (10(7)-10(8) bacteria.mL-1 after weaning). In spite of several inoculations, this cellulolytic species failed to establish in the rumen of lambs of group IV, which had received the less complex inoculum. The volatile fatty acid levels were very different from one lamb group to another. The more complex the inoculum administered to the animals, the higher the concentration.(ABSTRACT TRUNCATED AT 250 WORDS)

Establishment of ciliate protozoa in the rumen of conventional and conventionalized lambs: influence of diet and management conditions

The establishment of ciliate protozoa in the rumen was studied in conventional lambs reared under different conditions of management. The role of the microflora in the kinetics of this establishment was also investigated in conventionalized lambs. In lambs reared under farm conditions ciliate protozoa appeared in the following order: Entodinium (15-20 days), Polyplastron, Eudiplodinium, and Epidinium (20-25 days), and Isotricha (50 days). Entodinium was the most abundant (10(5)-10(6) ciliates mL-1). During the 3rd month, ciliates disappeared spontaneously in about 60% of the lambs during a period that varied from 1 to 4 weeks. In lambs fed only cow's milk Entodinium spp. and Polyplastron multivesiculatum became established at low levels. The results obtained with the conventionalized lambs demonstrate that the establishment of the ciliates in the rumen requires that the bacterial flora be well established beforehand.

Role of rumen protozoa in nitrogen digestion in sheep given two isonitrogenous diets

1. The effect of protozoa on digestion in the rumen was studied using either defaunated or faunated sheep. 2. Six wethers, each fitted with rumen and simple duodenal cannulas, were given two isonitrogenous diets containing either lucerne (Medicago sativa) hay (diet L) or sodium hydroxide-treated wheat straw (diet S). The diets were given in eight equal portions per day at 3-h intervals. The mean intake of dry matter, 53 g/kg body-weight0.75 per d, was similar for the two diets and each diet had a similar digestible organic matter content. Diet L promoted a large protozoal population and was rich in nitrogen sources of low rumen-degradability, while diet S supported a smaller protozoal population and was rich in rumen-degradable N. 3. Digesta flow at the duodenum was estimated by means of a dual-marker technique using chromium-mordanted lucerne hay and polyethylene glycol as markers. The microbial flow at the duodenum was estimated using diaminopimelic acid (DAPA), nucleic-acid purine bases (PB) and 35S incorporation simultaneously. The different microbial markers were compared in the defaunated sheep. Protozoal N contribution was estimated in faunated sheep. 4. Defaunated sheep had lower rumen ammonia concentrations and molar proportions of butyric acid than faunated sheep, but they had higher molar proportions of propionic acid. 5. Rumen organic matter digestion was reduced by defaunation, but this decrease was compensated for by increased intestinal digestion. 6. There was a net increase of N flow (approximately 10 g/d) between mouth and duodenum in defaunated sheep. This was explained by increases in both microbial and dietary N flows from the rumen compared with faunated sheep. 7. The influence of protozoa on solid- and liquid-phase retention times in the rumen is discussed, as well as the protozoal contribution to microbial N flow in the duodenum of faunated sheep.

Colonic metabolism of wheat starch in healthy humans. Effects on fecal outputs and clinical symptoms

To study the intracolonic digestion of starch, 5 healthy volunteers were maintained on a constant diet for 7 days. On the fourth day, the cecum was intubated and a suspension of raw wheat starch (50 g, in 500 ml of 154 mM NaCl and containing 10 g of polyethylene glycol 4000) was infused into the distal ileum at 2 ml/min. Hydrogen excretion in breath was measured, cecal contents were sampled, and symptoms were recorded. For the 2-3 days before and after starch infusions, fecal weight, pH, and percentage of dry matter were monitored; fecal outputs of starch, volatile fatty acids, lactic acid, ethanol, polyethylene glycol, alpha-amylase, nitrogen, and ammonia were also measured. A lactulose (10 g) hydrogen breath test was performed 5-7 days after the starch infusions. After the infusion of starch, concentrations of lactic and volatile fatty acids increased and pH decreased markedly in cecal contents. None of the fecal values changed significantly after starch, however, indicating that carbohydrate catabolism was nearly complete and that the colon absorbed the catabolic products efficiently. Abdominal symptoms, especially bloating, were noted by all subjects, and 2 subjects complained of cramping pain. No subject experienced diarrhea. The amounts of starch metabolized in the colon (47.3 +/- 2.9 g), as calculated from the excretion of H2 in breath compared to the hydrogen breath test after lactulose, were close to the actual load (50 g).

Determination of assay parameters for RNA analysis in bacterial and duodenal samples by spectrophotometry. Influence of sample treatment and preservation

A simple analytical procedure derived from that described by Zinn and Owens (1980), based on the determination of nucleic purine bases (RNA eq), was carried out to measure microbial nitrogen flow in the ruminant duodenum. Several procedures for sample preservation were tested; the efficiency of each step of the analytical method was also determined using high performance liquid chromatography (HPLC). The proposed method (RNA eq) was compared with two other methods considered as references (2-6 diaminopimelic acid and 35S incorporation) and microbial nitrogen flow was measured in defaunated sheep. The recovery of purine bases analysed by the Zinn and Owens method was generally good (101% pure bases; 90% when bases were added to bacterial samples; 96% when added to yeast RNA). The HPLC measurements allowed us to conclude that this spectrophotometric method is specific for purine bases, all pyrimidine bases being eliminated. Moreover, it was found that the method must be used on freeze-dried samples; storage at + 4 degrees C, defatting or freezing gave incorrect results. Using the described assay, we observed that microbial nitrogen flow at the duodenum of defaunated sheep was not significantly different from that obtained using more traditional markers such as sulphur-35 incorporation or diaminopimelic acid.

Effect of protozoa on rumen protein degradation in sheep

We have studied the contribution of ciliate protozoa to the degradation of dietary protein, utilizing 5 defaunated and 6 faunated sheep. Rumen samples from these animals were used as inocular for in vitro determination of the degradability of different protein sources: lupine grain, peanut and soybean cake, and fish meal. We also applied the in sacco method to measure the digestibility of soybean proteins. Two pore sizes (50 and 100 microns) were used in the in sacco study. The nitrogen degradation curve was constructed according to the mathematical model: P(t) = a + b (1-e-ct), and the parameters a, b, and c were determined for both faunated and defaunated animals. The proteolytic activity of the rumen contents was also determined using azocasein. The in vitro degradability of proteins was significantly less in defaunated than in faunated animals: 17, 19, 28 and 64% with lupine grain, peanut cake, soybean cake and fish meal proteins, respectively. The protozoal effect was greater when protein solubility was low. The in sacco study showed that neither the protozoa nor bag pore size had any effect on the protein fraction (a) immediately soluble in the rumen juice. However, both factors increased the insoluble, potentially degradable fraction "b" (P less than or equal to .01). Protozoa had a positive effect on the rate of degradation (c) of the fraction b. This effect was most clear with the 100 micron bags. The significant interaction between protozoa and pore size on factor "c" showed that large ciliate protozoa (100 microns) were directly involved in determining this parameter.(ABSTRACT TRUNCATED AT 250 WORDS)