Microbiological evaluation of the intraruminal in sacculus digestion technique

Meta-analysis of the effects of sulfate versus hydroxy trace mineral source on nutrient digestibility in dairy and beef cattle

Trace mineral (TM) source can potentially alter nutrient digestibility through effects on microbial populations. A meta-analysis was conducted to determine whether sulfate versus hydroxy (IntelliBond) sources of supplemental Cu, Zn, and Mn had any effect on dry matter intake (DMI), dry matter digestibility, and neutral detergent fiber (NDF) digestibility. All available cattle studies (8 studies, 12 comparisons) were used to estimate the effect size (hydroxy mean - sulfate mean). Factors included in the analysis were method of digestibility analysis (total collection, marker-based, or 24 h in situ), study design (randomized design or Latin square), beef (n = 5) versus dairy (n = 7) cattle, and days on treatment; these factors were retained when P < 0.05. Dry matter digestibility was increased by hydroxy TM in beef (1.64 ± 0.35 units) but not in dairy models (0.16 ± 0.13 units) relative to sulfate TM. The NDF digestibility increased significantly with hydroxy versus sulfate TM, but digestibility assessment method influenced this response. Studies using total collection or undigested NDF as a flow marker showed a significant increase (2.68 ± 0.40 units and 1.08 ± 0.31 units, respectively) in NDF digestibility for hydroxy versus sulfate TM; but studies utilizing 24-h in situ incubation did not detect any change (-0.03 ± 0.23 units). These observations may reveal differences in precision of measurement or may indicate mineral effects beyond the rumen; total collection is considered the gold standard method. Hydroxy TM did not affect DMI per animal or per unit of body weight relative to sulfate TM. In conclusion, feeding hydroxy versus sulfate TM does not appear to affect DMI but, depending on type of cattle and method of measurement, can increase dry matter digestibility and NDF digestibility, which may be explained by differences in solubility of the TM sources in rumen, differentially affecting fermentation.

Effects of Exogenous Fibrolytic Enzyme Derived from Trichoderma reesei on Rumen Degradation Characteristics and Degradability of Low-Tannin Whole Plant Faba Bean Silage in Dairy Cows

The objectives of this study were to (1) determine the effect of exogenous fibrolytic enzyme derived from Trichoderma reesei on dry matter (DM) and neutral detergent fibre (NDF) degradability of whole plant faba bean silage (Snowbird), (2) evaluate the effects of fibrolytic enzyme (FETR) on DM and NDF degradation kinetics of whole plant faba bean silage, and (3) compare the difference between in the vitro approach (DaisyII incubation method) and the in situ assay-biological approach (nylon bag technique) in the determination of degradability of dry matter (DMD) and neutral detergent fibre (NDFD). The fibrolytic enzyme from Trichoderma reesei was a mixture of xylanase and cellulase. The whole plant faba bean silage was treated with seven doses of fibrolytic enzyme, with 0 as a control and 0.25, 0.5, 0.75, 1, 1.25 and 1.5 mL of FETR/kg DM of silage. The results obtained from the in situ method show that fibrolytic enzyme cubically (p < 0.05) affected DMD and quadratically (p < 0.01) affected NDFD with increasing level of enzyme application. In vitro DM and NDF degradability were quadratically and cubically (p < 0.01) affected by the increasing dosage of enzyme. Correlation analysis between the in situ assay-biological approach and the In vitro DaisyII approach showed a strong correlation (r = 0.98, p < 0.01) on overall DMD and also a satisfactory relationship (r = 0.84, p < 0.01) was found on overall NDFD. The enzyme application showed a great impact on NDF rumen degradation kinetics by decreasing the undegradable fraction and increasing the potential degradable fraction and the effective degradable content of fiber. The washable (W) and potential degradation fraction (D) were linearly (p = 0.05) increased by the enzyme treatments. Therefore, the undegradable fraction was linearly decreased (p = 0.05) with increasing dosage of enzyme. Both bypass (BNDF) and effective degradable NDF (EDNDF) were cubically (p = 0.05) affected by fibrolytic enzyme. In conclusion, the exogenous fibrolytic enzyme derived from Trichoderma reesei highly impacted rumen degradation characteristics and degradability of whole plant faba bean silage and could be used to improve fibre digestion of whole plant faba silage in dairy cows.

In situ incubation sequence and its effect on degradation of food components when measured in the caecum of ponies

Three experiments were conducted to investigate the effect of bag incubation sequence on the degradation of food components in situ in the caecum of mature, caecally fistulated Welsh-cross pony geldings (mean live weight 278 kg) offered hay ad libitum. In experiment 1 a fibre-based commercial horse concentrate was incubated in situ using a forward (3, 5, 16, 8, 24, 48 h) or reverse (48, 24, 8, 16, 5, 3 h) incubation sequence. Dry matter (DM), crude protein (CP), neutral-detergent fibre (NDF) and acid-detergent fibre (ADF) degradation coefficients and calculated effective degradability (ED) values were determined. In experiment 2 unmolassed sugar-beet pulp (USBP), hay cubes (HC), soya hulls (SH) and a 2: 1 mixture of oat hulls: naked oats (OHNO) were incubated in situ as for experiment 1. In experiment 3 unprocessed barley (UB), micronized barley (MB), extruded barley (EB) and dehydrated grass (DHG) were incubated in situ according to slightly different forward or reverse incubation sequences of (2, 4, 6, 12, 8, 24, 48 h) and (48, 24, 8, 4, 12, 6, 2 h) respectively. In experiments 2 and 3 only DM degradation parameters were studied.

Of the three starch-based foods studied in experiment 3 (UB, MB and EB), incubation sequence did not significantly P > 0·05) affect any of the degradation parameters examined. Conversely however, of the six fibre-based foods which were examined across the three experiments, incubation sequence did significantly P < 0·05) affect in situ degradation parameters in the commercial horse concentrate in experiment 1, the SH food in experiment 2 and the DHG food in experiment 3. Depending on the food or food constituent studied (i.e. DM, CP, NDF or ADF) degradation coefficients a, b, c and a + b along with ED values calculated at fractional outflow rates of 0·05 and 0·025 could all be statistically different CP < 0·05) according to whether a forward or reverse incubation sequence was used. It is postulated that this effect is related to the basic digestive physiology of the equine caecum which is small, digesta passage rate through it is fast and digesta volumes can vary considerably. These factors may interact to create a considerable degree of non-uniformity within the caecal digesta pool in which in situ bags are incubated. Consequently, it is recommended that in future in situ experiments in the equine hindgut, animals are offered ad libitum diets in an attempt to minimize variation within the caecum. It is also recommended that in situ experimental protocols incorporate more than one incubation sequence when the degradation parameters of fibrous foods are studied in equids.

Compartmental flux andin situmethods underestimate total feed nitrogen as judged by the omasal sampling method due to ignoring soluble feed nitrogen flow

The objective of the present study was to estimate ruminal feed N outflow in lactating cows using the omasal sampling, compartmental flux orin situmethod. A total of five ruminally fistulated Finnish Ayrshire dairy cows were used in a 5 × 5 Latin square study with 21 d periods. Experimental silages of grass or red clover harvested at two stages of maturity in addition to a supplement of 9·0 kg concentrate/d were fed to the cows.In vivoomasal N flow was determined using the omasal sampling technique. Ruminalin situN flow was calculated from N intake and degradability (38 μm nylon bags). The samples of ruminal contents and faeces were divided into seven particle-size fractions by wet sieving; the concentrations of indigestible neutral-detergent fibre and N were used to calculate N flow in the compartmental flux method.In vivoomasal N flow was greater for the red clover silage diets than for the grass silage diets. The N flow calculated using the compartmental flux technique and that calculated using thein situtechnique were highly correlated, but both were less than and poorly correlated with thein vivoN flow. In bothin situand compartmental flux techniques, forage maturity increased the particle-associated N flow, with the increase being significantly greater for the red clover diets than for the grass silage diets. In conclusion, the compartmental flux andin situmethods described the N flow associated with the particle fractions rather than the total ruminal outflow of feed N.

Short communication: Evaluation of acid-insoluble ash and indigestible neutral detergent fiber as total-tract digestibility markers in dairy cows fed corn silage-based diets

The objective of this experiment was to evaluate acid-insoluble ash (AIA) and indigestible NDF (iNDF) as intrinsic digestibility markers in comparison with total fecal collection (TC) in dairy cows fed corn silage- and alfalfa haylage-based diets. The experiment was part of a larger experiment, which involved 8 Holstein cows [102±28.4 d in milk, 26.4±0.27 kg/d of dry matter (DM) intake, and 43±5.3 kg/d milk yield]. The experimental design was a replicated 4×4 Latin square with the following treatments: metabolizable protein (MP)-adequate diet [15.6% crude protein (CP); high-CP], MP-deficient diet (14.0% CP; low-CP), and 2 other low-CP diets supplemented (top-dressed) with ruminally protected Lys or Lys and Met. Data for the 3 low-CP diets were combined for this analysis. Total feces were collected for 5 consecutive days during each period to estimate total-tract apparent digestibility. Digestibility was also estimated using AIA (digestion with 2 N HCl) and iNDF (12-d ruminal incubation in 25-μm-pore-size bags). Significant diet × digestibility method interactions were observed for fecal output of nutrients and digestibility. Fecal output of nutrients estimated using AIA or iNDF was lower compared with TC and fecal output of DM, organic matter, and CP tended to be higher for iNDF compared with AIA for the high-CP diet. For the low-CP diet, however, fecal output of all nutrients was lower for AIA compared with TC and was higher for iNDF compared with TC. Data from this experiment showed that, compared with TC, AIA underestimated fecal output and overestimated digestibility, particularly evident with the fiber fractions and the protein-deficient diet. Compared with TC, fecal output was overestimated and digestibility of the low-CP diet was underestimated when iNDF was used as a marker, although the magnitude of the difference was smaller compared with that for AIA. In the conditions of the current study, iNDF appeared to be a more reliable digestibility marker than AIA in terms of detecting dietary differences in apparent digestibility of some nutrients, but significant diet × marker interactions existed that need to be considered when estimating total-tract digestibility using intrinsic markers.

Effect of diet composition and incubation time on feed indigestible neutral detergent fiber concentration in dairy cows

Indigestible neutral detergent fiber (NDF) predicts forage digestibility accurately and precisely when determined by a 288-h ruminal in situ incubation, and it is an important parameter in mechanistic rumen models. The long incubation time required is a disadvantage. Further, intrinsic cell wall characteristics of feeds should be determined under ideal conditions for fiber digestion. The objective of this study was to determine the effects of diet composition and rumen incubation time on the concentrations of indigestible NDF (iNDF) for a wide range of feeds in dairy cows. Additionally, predicted concentrations of unavailable NDF generated using the National Research Council (NRC) model and the Cornell Net Carbohydrate and Protein System (CNCPS) were evaluated. Indigestible NDF was evaluated in 18 feeds using 4 cows in a split-split plot design. Treatments were in a 3 × 3 factorial arrangement, consisting of different diets and incubation times. Diet composition was primarily varied by changing the level of concentrate supplementation between 190 (low), 421 (medium), and 625 (high)g/kg of diet dry matter (DM). Grass silage was used as the basal forage for all cows. The feeds were incubated for 144, 216, and 288 h. Indigestible NDF was determined from 2-g samples weighed into polyester bags with a pore size of 12 µm and a pore area equal to 6% of the total surface area, giving a sample size to surface ratio of 10mg/cm(2). Across all feeds, the measured iNDF concentrations ranged from 6 to 516 g/kg of DM. The feed iNDF concentration was not affected by the cow used, but diet composition had a significant effect. The mean measured iNDF concentrations for cows consuming low-, medium-, and high-concentrate diets were 178, 186, and 197 g/kg of DM, respectively. The incubation time also affected the feed iNDF concentrations, which averaged 199, 185, and 177 g/kg of DM for 144-, 216-, and 288-h incubations, respectively. We also observed significant interactions between incubation time and feed, and between diet composition and feed, with fiber-rich feeds being most sensitive to these factors. The evaluation of model predictions of unavailable NDF indicated poor precision with prediction errors of 56 (NRC) and 84 (CNCPS)g/kg of DM. Indigestible NDF should be determined based on 288-h ruminal in situ incubations in cows consuming diets with a low proportion of concentrate to represent the feed fraction that is unavailable to the animal.

Effects of replacing dietary starch with neutral detergent-soluble fibre on ruminal fermentation, microbial synthesis and populations of ruminal cellulolytic bacteria using the rumen simulation technique (RUSITEC)

A rumen simulation technique (RUSITEC) apparatus with eight 800 ml fermenters was used to investigate the effects of replacing dietary starch with neutral detergent-soluble fibre (NDSF) by inclusion of sugar beet pulp in diets on ruminal fermentation, microbial synthesis and populations of ruminal cellulolytic bacteria. Experimental diets contained 12.7, 16.4, 20.1 or 23.8% NDSF substituted for starch on a dry matter basis. The experiment was conducted over two independent 15-day incubation periods with the last 8 days used for data collection. There was a tendency that 16.4% NDSF in the diet increased the apparent disappearance of organic matter (OM) and neutral detergent fibre (NDF). Increasing dietary NDSF level increased carboxymethylcellulase and xylanase activity in the solid fraction and apparent disappearance of acid detergent fibre (ADF) but reduced the 16S rDNA copy numbers of Ruminococcus albus in both liquid and solid fractions and R. flavefaciens in the solid fraction. The apparent disappearance of dietary nitrogen (N) was reduced by 29.6% with increased dietary NDSF. Substituting NDSF for starch appeared to increase the ratios of acetate/propionate and methane/volatile fatty acids (VFA) (mol/mol). Replacing dietary starch with NDSF reduced the daily production of ammonia-N and increased the growth of the solid-associated microbial pellets (SAM). Total microbial N flow and efficiency of microbial synthesis (EMS), expressed as g microbial N/kg OM fermented, tended to increase with increased dietary NDSF, but the numerical increase did not continue as dietary NDSF exceeded 20.1% of diet DM. Results suggested that substituting NDSF for starch up to 16.4% of diet DM increased digestion of nutrients (except for N) and microbial synthesis, and further increases (from 16.4% to 23.8%) in dietary NDSF did not repress microbial synthesis but did significantly reduce digestion of dietary N.

Comparison of some aspects of the in situ and in vitro methods in evaluation of neutral detergent fiber digestion

The objective of the present study was to compare digestion rates (kd) of NDF for different feeds estimated with the in situ method or derived from an automated gas in vitro system. A meta-analysis was conducted to evaluate how in situ derived kd of NDF related to in vivo digestibility of NDF. Furthermore, in vitro true digestibility of the feed samples incubated within filter bags or dispersed in the medium was compared, and kd for insoluble and soluble components of those feeds were estimated. Four different concentrates and 4 forages were used in this study. Two lactating Swedish Red cows fed a diet of 60% grass silage and 40% concentrate on DM basis were used for in situ incubations and for collection of rumen fluid. The feed samples were ground through a 2.0-mm screen before the in situ incubations and a 1.0-mm screen before the in vitro gas incubations. In situ nylon bags were introduced into the rumen for determination of kd of NDF. Additional kinetic data were produced from isolated NDF and intact samples subjected to in vitro incubations in which gas production was recorded for 72 h. Samples were weighed in the bottles or within filter bags (for fiber and in vitro studies) that were placed in the bottles. The interaction between feed and method was significant (P < 0.01); kd of NDF for grass hay tended (P = 0.06) to be less whereas kd of NDF for alfalfa, barley grain, canola meal, and dried sugar beet pulp were greater (P < 0.01) when estimated with the in situ method than from gas production recordings. The meta-analysis suggested that in situ derived kd of NDF were biased and underestimated in vivo digestibility of NDF. Digestion rates of the intact samples were lower for all feeds, except for the hay, when incubated within the bags compared with dispersed in the medium (P < 0.01). Less OM and NDF were digested for all feeds when incubated within bags than dispersed in the medium (P < 0.01). It is concluded from the in vitro study that microbial activity within the bags is less than in the medium. Significant interactions between method (in situ vs. in vitro) and feed suggest that one or both methods result in biased estimates of digestion kinetics.

Influência de subprodutos de oleaginosas sobre parâmetros ruminais e a degradação da matéria seca e da proteína bruta

Avaliou-se o efeito da adição de subprodutos de oleaginosas na dieta de ovinos em substituição ao farelo de soja. Foram distribuídos quatro ovinos Santa Inês, com peso corporal de, aproximadamente, 40kg, canulados no rúmen, em quadrado latino (4x4), com quatro dietas e quatro períodos, analisados por regressão para a avaliação da degradação ruminal, dos valores de pH e das concentrações de nitrogênio amoniacal in vivo. Os subprodutos foram as tortas de amendoim, girassol e soja, em dietas isonitrogenadas, com 70% de concentrado e 30% de volumoso (feno de tifton). Não foi observado efeito da interação tempo x dieta para os valores de pH e concentração ruminal de nitrogênio amoniacal (P>0,05). O pH apresentou valor médio de 6,2. As concentrações ruminais de nitrogênio amoniacal não foram afetadas, com valor médio de 29,9mg/dL. Não foram observadas diferenças (P>0,05) nas taxas de degradação da matéria seca e na degradabilidade potencial.

True dry matter digestibility of feeds evaluated in situ with different bags and in vitro using rumen fluid collected from intact donor cows

The aim of the study was to determine the comparability of the true dry matter digestibility (TDMd) achieved in situ with either traditional nylon bags (IS nylon) or synthetic filter bags (IS filter), and in vitro with either conventional bottles (CB) or the DaisyII incubation technique, using rumen fluid collected by oro-ruminal suction from intact cows. The four TDMd results were compared by linear regression. For each method, 11 feeds were incubated for 48 h in two separate incubations. The reproducibility of TDMd measurements was 97.9%, 95.1%, 98.8% and 96.0% for IS nylon, IS filter, CB and DaisyII, respectively. The determination coefficient, the slope (b), and the significant difference of the slope from unity, of the linear relationship between TDMd values (g/kg DM) were as follows: IS nylon v. IS filter, R2 = 0.97, b = 0.86, P = 0.02; IS nylon v. CB, R2 = 0.90, b = 1.02, P = 0.27; IS nylon v. DaisyII, R2 = 0.90, b = 1.06, P < 0.01; and IS filter v. DaisyII, R2 = 0.95, b = 0.98, P = 0.13. In situ filter bags and DaisyII underestimated the TDMd values compared with IS nylon bags and CB, respectively. In situ, the replacement of nylon with filter bags could simplify the procedure of analysis, with less manipulation of residuals and less labour, and offers the possibility to increase the number of samples analysed simultaneously. The close relationships found among methods suggest that rumen fluid collected from intact cows can produce in vitro estimates of TDMd at 48 h well correlated with those obtained in situ.

Metagenomic discovery of biomass-degrading genes and genomes from cow rumen

The paucity of enzymes that efficiently deconstruct plant polysaccharides represents a major bottleneck for industrial-scale conversion of cellulosic biomass into biofuels. Cow rumen microbes specialize in degradation of cellulosic plant material, but most members of this complex community resist cultivation. To characterize biomass-degrading genes and genomes, we sequenced and analyzed 268 gigabases of metagenomic DNA from microbes adherent to plant fiber incubated in cow rumen. From these data, we identified 27,755 putative carbohydrate-active genes and expressed 90 candidate proteins, of which 57% were enzymatically active against cellulosic substrates. We also assembled 15 uncultured microbial genomes, which were validated by complementary methods including single-cell genome sequencing. These data sets provide a substantially expanded catalog of genes and genomes participating in the deconstruction of cellulosic biomass.

Dynamics of initial colonization of nonconserved perennial ryegrass by anaerobic fungi in the bovine rumen

Anaerobic fungi (Neocallimastigales) are active degraders of fibrous plant material in the rumen. However, only limited information is available relating to how quickly they colonize ingested feed particles. The aim of this study was to determine the dynamics of initial colonization of forage by anaerobic fungi in the rumen and the impact of different postsampling wash procedures used to remove loosely associated microorganisms. Neocallimastigales-specific molecular techniques were optimized to ensure maximal coverage before application to assess the population size (quantitative PCR) and composition (automated ribosomal intergenic spacer analysis) of the colonizing anaerobic fungi. Colonization of perennial ryegrass (PRG) was evident within 5 min, with no consistent effect of time or wash procedure on fungal population composition. Wash procedure had no effect on population size unlike time, which had a significant effect. Colonizing fungal population size continued to increase over the incubation period after an initial lag of c. 4 min. This dynamic differs from that reported previously for rumen bacteria, where substantial colonization of PRG occurred within 5 min. The observed delay in colonization of plant material by anaerobic fungi is suggested to be primarily mediated by the time taken for fungal zoospores to locate, attach and encyst on plant material.

Methods to study degradation of ruminant feeds

Ruman degradation is crucial in the supply of dietary nutrients to meet the nutrient demands of the anaerobic microbes and body tissues of ruminant animals. Therefore, it is essential to study the dynamics of rumen degradation of various feeds before their potential use to formulate nutritious diets for ruminant animals. Amongst many methods that have been used in the past, thein saccomethod has been the most effective method to study rumen degradation. However, this method is undesirable due to its implications for animal welfare and costs. While manyin vitromethods have been tested as possible alternatives to thein saccomethod to study rumen degradation of feeds, they were unable to remove the need to use fistulated animals to obtain rumen fluid. Although solubility, enzyme- and faeces-basedin vitromethods do not require rumen fluid, they still need data from either thein saccomethod or the rumen fluid-basedin vitromethods for comparison and validation. Therefore, there is a need to developin vitromethods that do not require the need to surgically modify ruminants to obtain rumen fluid to study rumen degradation. We review the potentials and problems associated with the existing methods to study rumen degradation and their implications for the animal industry in different situations.

Fatty Acid Profiles Associated with Microbial Colonization of Freshly Ingested Grass and Rumen Biohydrogenation

Two in situ studies were conducted to examine the use of odd-chain fatty acid profiles to study microbial colonization of freshly ingested herbage in the rumen as well as fatty acid biohydrogenation. In the first study, fresh perennial ryegrass was subjected to a range of sample preparation methods before incubation in the rumen for 2 or 7 h. In the second study, fresh perennial ryegrass was chopped into 1-cm lengths and incubated in polyester bags in the rumen for 2, 8, and 24 h. After removal of bags from the rumen, 4 different washing methods, ranging from manual squeezing to machine washing, were applied. Fatty acids were extracted from washed residues and determined, as methyl esters, by gas chromatography. The main odd-chain fatty acids (with the exception of anteiso C(15:0)) were not found in fresh grass and were useful markers of the effects of incubation time, sample preparation method, and washing method on microbial colonization/contamination. The concentration of these and other odd-chain fatty acids increased with incubation time in both studies. The results indicate rapid and continued microbial colonization of freshly ingested forages, although patterns of odd-chain fatty acids did not reveal any further information about the types of bacteria-colonizing herbage. Principal component, biplot analysis provided a useful overall description of the processes of microbial colonization and degradation of plant fatty acids on fresh herbage incubated in the rumen. Bolus formation during mastication and ingestion results in extensive damage to herbage; none of the techniques (cutting, crushing, and drying/grinding) investigated in this work was able to replicate the effects of bolus formation in the animal. The study provided further evidence of loss of unfermented feed particles through polyester bag pores, especially when feeds are dried and ground. Biohydrogenation of the polyunsaturated fatty acids of fresh herbage was used principally by solid-associated bacteria to enable them to take up high levels of trans-11 C(18:1) and C(18:0) fatty acids. Although trans-11 C(18:1) was strongly associated with bacterial markers (odd- and branched-chain fatty acids), its precursor (cis-9, trans-11 C(18:2)) was not associated with bacterial variation, suggesting that its production in the rumen under these conditions was mainly extracellular.

Effects of size of ingestively masticated fragments of plant tissues on kinetics of digestion of NDF

Ingestively masticated fragments were collected and sized via sieving. Different sizes of esophageal masticate and ruminal digesta fragments, and ground fragments of larger masticated pieces were incubated in vitro, and undigested NDF remaining at intervals of up to 168 h of incubation was determined. The ruminal age-dependent time delay (tau) for onset of digestion of NDF was positively correlated (P < 0.004) with the mean sieve aperture estimated to retain 50% of the fragments between successive sieve apertures (MRA). Degradation rate of potentially degradable NDF (PDF) and level of indigestible NDF were not related (P > 0.10) to MRA of masticated and ground fragments. Estimates of tau were positively related to MRA, with slopes of bermudagrass < corn silage < ruminal fragments of corn silage. It was concluded that fragment size-, and consequently, ruminal age-dependent onset of PDF degradation of a mixture of different fragment sizes results in an age-dependent rate of degradation of the more rapidly degrading of two subentities of PDF. Models are proposed that assume a tau before onset of simultaneous degradation of PDF from two pools characterized as having gamma-modeled age-dependency and age-constant rates. The ruminal age-dependent pool seems to be associated with the faster-degrading pool, and its rate parameter increases with range in MRA in the population of fragments. Conceptually, the ruminal age-dependent rate parameter for PDF degradation seems to represent a composite of several effects: 1) effects of the size-dependent tau; 2) range in MRA of the population of ingestively masticated fragments; and 3) subentities of PDF that degrade via more rapid age-dependent rates compared with subentities of PDF that degrade via age-constant rates. The estimated fractional rates of ruminative comminution of ingestively masticated fragments (0.060 to 0.075/h) were of a magnitude similar to the mean fractional rates of PDF digestion (0.030 to 0.085/h), which implies that ruminative comminution may be first-limiting to fractional rate of PDF digestion. The in vivo roles of ingestive and ruminative mastication of fragments on PDF degradation must be considered in any kinetic system for estimating PDF digestion in the rumen. These results and others in the literature suggest that the rate of surface area exposure rather than intrinsic chemical attributes of PDF may be first-limiting to degradation rate of PDF in vivo.

Degradabilidad ruminal de fracciones de carbohidratos en forrajes tropicales determinada por métodos in vitro e in situ

Cuatro gramíneas tropicales y una leguminosa se evaluaron para conocer la degrada­bilidad ruminal del material entero o completo (ME), el residuo insoluble en etanol (RIE) y la pared celular (FDN), mediante las técnicas de producción de gas (in vitro) y degradabilidad en bolsa de nylon (in situ). Se escogieron las gramíneas Dichantium aristatum (Angleton), Brachiaria decumbens (Braquiara), Bothriochloa pertusa (Colosuana o Kikuyina) y Pennisetum clandestinum (Kikuyo), además de la leguminosa Medicago sativa (alfalfa). Las cuatro gramíneas se cosecharon en la edad adecuada para pasto­reo (Kikuyo con 56 días de descanso, 30 días para Braquiara, 35 días para Angleton y 35 para Colosuana). La alfalfa se cosechó en floración (60 días de rebrote). La degradabilidad in vitro se determinó mediante la cuantificación de residuo seco a 105 °C, después de 48 horas de incubación de una muestra de 100 mg de cada fracción de forraje y lavado con detergente neutro. La degradabilidad in situ se determinó de acuerdo a las técnica de la bolsa de nylon, en bolsas de poliéster utilizando las mis­mas fracciones de forraje, con 3,0 g de muestra por bolsa e incubación por 48 horas en el rumen de una vaca Holstein no lactante ni gestante, alimentada con Kikuyo bajo pastoreo libre y permanente. Los porcentajes de materia seca (MS) degradada en las dos técnicas se compararon mediante un análisis de varianza con el procedimiento General Linear Models (GLM) de SAS® para cada fracción. La degradabilidad ruminal en los cuatro forrajes, mediante la técnica in vitro fue superior a la degradabilidad en bolsa (P < 0,01) para todas las fracciones, siendo la correlación entre las dos técnicas alta (0,87, P < 0,001). La degradación total in vitro para los sustratos fue 72,4, 46,3, 78,9, 52,1 y 80,8%, para el ME de alfalfa, Angleton, Brachiaria, Colosuana y Kikuyo, respec­tivamente. Para el ME en todos los pastos la correlación entre los dos métodos fue de 0,93 (P < 0,01). La degradación in situ del ME fue de 71,7, 26,6, 63,9, 33,4 y 71,4% para Alfalfa, Angleton, Brachiaria, Colosuana y Kikuyo, respectivamente y fue diferente a la degradación in vitro (P < 0,01). La degradación in vitro del RIE fue de 53,2, 43,2, 75,2, 49,1 y 76,4% para los cinco forrajes respectivamente y 53,2, 22,7, 47,2, 27,6, y 61,7% para la degradación in situ del RIE en los cinco forrajes respectivamente, siendo diferentes los dos métodos (P < 0,01). La degradación in vitro de FDN fue 45.7, 47,2, 70,1, 53,2 y 75,0% para cada pasto respectivamente y de: 38,0, 25,8, 42,2, 36,3 y 52,8% para la degradación in situ del FDN en los cinco pastos, respectivamente y los valores fueron diferentes a con respecto al método in vitro (P<0,05). La correlación entre los dos métodos fue: 0,86 para el RIE y 0,74 para FDN en todos los forrajes (P < 0,001 y P < 0,005). Las diferencias entre la degradabilidad in vitro e in situ se pueden atribuir a los procedimientos de lavado de los residuos, a exposición inadecuada de las bolsas a la acción de los microorganismos por compactación del sustrato en la bolsa o a una reducción en la actividad fibrolítica de las bacterias del rumen en las bolsas. Se esperaría que la desaparición del sustrato fuera más alta por el escape de partículas pequeñas a través de los poros de la bolsa y al efecto de la tasa de pasaje dentro del rumen, condiciones que no ocurren en la degradación in vitro. 

Evidence in support of a role for plant-mediated proteolysis in the rumens of grazing animals

The present work aimed to differentiate between proteolytic activities of plants and micro-organisms during the incubation of grass in cattle rumens. Freshly cut ryegrass was placed in bags of varying permeability and incubated for 16 h in the rumens of dairy cows that had previously grazed a ryegrass sward, supplemented with 4 kg dairy concentrate daily. Woven polyester bags (50 microm pore size) permitted direct access of the micro-organisms and rumen fluid enzymes to the plant material. The polythene was impermeable even to small molecules such as NH(3). Dialysis tubing excluded micro-organisms and rumen enzymes/metabolites larger than 10 kDa. DM loss was 46.3 % in polyester, 36.2 % in polythene and 38.1 % in dialysis treatments. It is possible that the DM loss within polythene bags occurred due to a solubilisation of plant constituents (e.g. water-soluble carbohydrates) rather than microbial attachment/degradation processes. The final protein content of the herbage residues was not significantly different between treatments. Regardless of bag permeability, over 97 % of the initial protein content was lost during incubations in situ. Electrophoretic separation showed that Rubisco was extensively degraded in herbage residues whereas the membrane-associated, light-harvesting protein remained relatively undegraded. Protease activity was detected in herbage residues and bathing liquids after all incubation in situ treatments. Although rumen fluid contains proteases (possibly of plant and microbial origin), our results suggest that, owing to cell compartmentation, their activity against the proteins of intact plant cells is limited, supporting the view that plant proteases are involved in the degradation of proteins in freshly ingested herbage.

Biochemical and Microbiological Evidence for Fermentative Digestion in Free‐Living Land Iguanas (Conolophus pallidus) and Marine Iguanas (Amblyrhynchus cristatus) on the Galápagos Archipelago

Herbivorous lizards are potentially capable of high digestive efficiency, but the presence of an indigenous microbial population has been implied from measurements of activity rather than directly studied. This study is the first to provide direct biochemical and microbiological evidence for fermentative digestion in free-living land iguanas (Conolophus pallidus) and marine iguanas (Amblyrhynchus cristatus) from the Galapagos archipelago. In marine iguanas, the stomach and large capacious colon contained ca. 32% and 60%, respectively, of the weight of total gut content. Total volatile fatty acid concentration was ca. 150 and 180 mM, respectively, for marine and land iguanas. Molar proportions of acetate, propionate, and butyrate (80.3%, 9.5%, and 3.5%) in land iguana fecal samples were similar to those for marine iguanas. Examination of fecal samples using confocal and transmission electron microscopy, as well as cultivable counts, revealed a dense and diverse population of bacteria, with spores prominent. Total culturable counts of anaerobes (2.22x10(8) g(-1) wet weight of fecal material) outnumbered aerobes on average by a factor of ca. 700. Combined, these results strongly support the contention that these unique herbivorous lizards are largely dependent on the presence and metabolic activities of a resident bacterial population in order to hydrolyze and ferment plant polymers that are indigestible to the host.

Kinetics of in sacco fiber-attachment of representative ruminal cellulolytic bacteria monitored by competitive PCR

Stems of orchardgrass hay in nylon bags were incubated in the rumens of three ruminally fistulated sheep to monitor the rate and extent of fiber attachment by the representative ruminal cellulolytic bacteria via competitive polymerase chain reaction. After incubation for 5 min, the numbers of Fibrobacter succinogenes and the two ruminococcal species attached to stems were 10(5) and 10(4)/g dry matter (DM) of stem, respectively. At 10 min, the numbers of all three species attached to stems increased 10-fold. Thereafter, attached cell numbers of the three species gradually increased and peaked at 24 h (10(9)/g DM for F. succinogenes and 10(7)/g DM for Ruminococcus flavefaciens) or 48 h (10(6)/g DM for Ruminococcus albus). On the other hand, cell numbers of all three species in the whole digesta were constant over 24 h. Changes in the rate of in sacco neutral detergent fiber disappearance of hay stem, which showed a linear increase up to 96 h, were not synchronized with changes in cellulolytic bacterial mass. These results suggest that sufficient numbers of cells of the three cellulolytic species to move to new plant fragments are present at the start of incubation, the initial attachment to new plant matter is mostly accomplished within 10 min and then bacterial growth and fibrolytic action follow. F. succinogenes was most dominant, both in the whole rumen digesta and on the suspended hay stems, demonstrating the ecological and functional significance of this species in ruminal fiber digestion.

Effect of the tropical forage calliandra on microbial protein synthesis and ecology in the rumen

AIMS

To determine the effect of condensed tannins in Calliandra calothyrsus (calliandra) on rumen microbial function.

METHODS AND RESULTS

Microbial populations, ruminal protein synthesis and fermentation end-products were measured in sheep fed roughage hay supplemented with calliandra (30%), with and without inclusions of polyethylene glycol (PEG) to counteract the effect of tannin. Molecular and conventional enumeration techniques were used to quantify rumen bacteria, fungi and protozoa, and protein synthesis was predicted from estimates of urinary purine excretion. The total number of cellulolytic bacteria, including populations of Fibrobacter succinogenes and Ruminococcus spp., was significantly lower in sheep supplemented with calliandra and these populations increased when animals were treated with PEG. By contrast, protozoa and fungi and the microbial group containing Bacteroides-Porphyromonas-Prevotella bacteria appeared to be less affected. The efficiency of microbial protein synthesis in the rumen was not altered significantly.

CONCLUSION

Calliandra caused significant shifts in rumen microbial populations without changing the efficiency of protein synthesis.

SIGNIFICANCE AND IMPACT OF THE STUDY

The effect of calliandra tannins on rumen digestion may result more from complexing with nutrients than direct inhibition of micro-organisms.

Enzyme activities of rumen particles and feed samples incubated in situ with differing types of cloth

Three ruminally cannulated non-lactating dairy cows were used to investigate the effects of six different bag cloth types with pore size (microns): free surface area (%) ratios of 200:45, 41:33, 16:5, 10:2, 6:5 and 1:2 respectively on the disappearance of grass silage DM and neutral-detergent fibre (NDF), and on particle-associated carboxymethylcellulase (EC 3.2.1.4; CMCase) and xylanase (EC 3.2.1.8) activities extracted from feed residues. Another objective was to compare microbial activity inside the bags and in rumen ingesta. Rumen incubation periods were 3, 6, 12, 24, 48 and 96 h. DM and NDF disappearance and particle-associated enzyme activities were greatly reduced with the smaller pore size and/or open surface area. Re-analysing some of the data as a 2 x 2 factorial (pore size x free surface area) indicated that, generally, free surface area rather than pore size affected the disappearance of feed components and particle-associated enzyme activities. Enzyme activities were highly correlated with NDF disappearance at 6-48 h of incubation. Cumulative area under CMCase and xylanase activity curves explained 0.79 and 0.88 of the variation in NDF disappearance when different cloth type and 6-48 h incubation data were combined. Weighted mean enzyme activities inside the bags were less than 0.35 those in rumen ingesta. The highest activity values inside the bags (24 or 48 h) were less than 0.50 those found in rumen ingesta. The lower microbial activity inside the bags explains the slower rates of NDF digestion reported with in situ techniques than with rumen evacuation techniques. The general assumption of similar microbial activity inside the bags and in rumen ingesta is not justified by the present results, and caution must be taken in interpreting in situ results quantitatively for feed evaluation systems.

Ruminal and total plant cell-wall digestibility estimated by a combined in situ method utilizing mathematical models

Three ruminally and duodenally cannulated non-lactating Finnish Ayrshire cows were used to investigate ruminal and intestinal digestion of cell-wall carbohydrates by a combined in situ method. Five grasses cut at 10 d intervals were incubated in the rumen for 0, 6, 12, 24, 48, 72 and 96 h, and the undegraded residues were exposed to intestinal digestion. With advancing maturity of grass both the rate and extent of cell-wall digestion decreased. At early stages of growth the decreases were faster for the rate of digestion and at late stages of growth for the extent of digestion. Applying a passage rate of 0.02/h in one compartmental rumen model resulted in digestibility values markedly lower than typically observed in vivo. However, applying a rumen model incorporating a selective retention of particles and time-dependent release of particles from the non-escapable pool resulted in much higher digestibility values. Recovery of lignin after 96 h ruminal incubation with a subsequent mobile-bag incubation was very low (from 244 to 460 mg/g). Intestinal disappearance of neutral-detergent fibre (NDF) and hemicellulose decreased with advancing maturity of grass and with increasing length of preceding ruminal incubation period, i.e. with decreasing potential digestibility of the material. Disappearance of hemicellulose was much greater than that of cellulose for intact grasses but the difference diminished with increasing length of preceding rumen incubation period. On average, 195 mg/g of potentially digestible NDF disappeared from the mobile bags in the intestines. The post-ruminal digestion as a proportion of the total NDF digestibility varied between 0.034 and 0.058. Despite methodological problems both in ruminal in situ and intestinal mobile bag techniques, these methods can be used to investigate ruminal and intestinal cell-wall digestion and to partition cell-wall digestibility between ruminal and post-ruminal digestion providing that appropriate rumen models are used.

The role of the large intestine in post-ruminal digestion of feeds as measured by the mobile-bag method in cattle

To study the importance of site of recovery and other factors related to mobile-bag (MB) digestion values, two consecutive experiments in which diets were applied in a 3 x 3 Latin square design, were carried out with cannulated growing heifers. In Expt 1, several types of experimental feed were exposed to intestinal digestion in mobile bags made of two cloth types and filled with intact or rumen-undegradable (RUD) feed material to be recovered either from the ileum (IB) or faeces (FB). In Expt 2, mean retention time (MRT) of Yb-labelled digesta particles within the intestine and in vivo digestibility of diets were measured. With vegetable concentrates, FB resulted generally in slight overestimation of small-intestinal dry matter and N digestion, while with meat-and-bone meal no difference between FB and IB was found. The respective N digestibility of RUD late-cut silage was clearly underestimated as measured from FB. The disappearance of neutral-detergent fibre (NDF) of all feeds under test was higher from FB than from IB. It was not possible to isolate the influence of the large intestine on the MB values by changing bag cloth type. Irrespective of the longer retention time of bags and longer MRT of Yb in the intestine on a low as compared with a high level of feeding, only NDF disappearance of feeds increased due to lower feeding level. Altering the diet type to increase large-intestinal fermentation, as indicated in vivo, usually had no effect on the MB values. It is concluded that the site of collection of bags does not practically affect small-intestinal digestion values of feed N, unless the feed is rich in fibre.

Effect of fiber source on short-chain fatty acid production and on the growth and toxin production by Clostridium difficile

BACKGROUND

Fermentable fiber promotes the growth of resident gut microbes, which modify the environment of the gastrointestinal tract and thus prevent colonization by Clostridium difficile.

METHODS

An in vitro system with pigs as fecal inoculum donors was used to estimate fiber fermentability and changes in intestinal microbiota.

RESULTS

Acetate and propionate production (mumol/mg substrate fermented/day) was greatest for gum arabic (1013.4 and 704.1, respectively); butyrate production was greatest for xylo-oligosaccharide (345.6). Growth of total anaerobes and clostridia was greatest for gum arabic (21.2 and 16.2 x 10(8) counts/ml, respectively) and xylo-oligosaccharides (21.0 and 19.6 x 10(8) respectively); growth of acidogenic bacteria was greatest with fructo-oligosaccharide (6.7 x 10(8) counts/ml). No culturable counts of C. difficile were obtained, nor was toxin A detected.

CONCLUSIONS

Fermentable fibers support the growth of indigenous intestinal bacteria, particularly acidogenic bacteria, and yield large amounts of short-chain fatty acids with decreased gut pH. These factors contribute to the prevention of growth and toxin elaboration by C. difficile.

The effect of sucrose supplements on particle-associated carboxymethylcellulase (EC 3.2.1.4) and xylanase (EC 3.2.1.8) activities in cattle given grass-silage-based diet

Carboxymethylcellulase (EC 3.2.1.4; CMCase) and xylanase (EC 3.2.1.8) activities were assayed in rumen fluid and from microbes closely associated either with rumen particulate material or with feed particles incubated in nylon bags in the rumen of cattle. The cattle were fitted with a permanent rumen cannula and a simple 'T'-piece duodenal cannula and were given four diets in a 4 x 4 Latin Square experiment. The basal diet (diet C) consisted of grass silage, barley and rapeseed meal (700, 240 and 60 g/kg total dry matter (DM)) given at the rate of 5.3 kg/d or supplemented with 1.0 kg sucrose/d given twice daily (diet S), twice daily with 0.25 kg sodium bicarbonate/d (diet B) or as a continuous intrarumen infusion (diet I). Giving sucrose supplements decreased CMCase and xylanase activities extracted from microbes associated with rumen particulate material or feed particles incubated in nylon bags as compared with diet C. Supplementation of the sucrose diet with sodium bicarbonate resulted in higher CMCase and xylanase activities than other sucrose diets (S and I). Particle-associated CMCase and xylanase activities were found to be very sensitive in detecting differences in the rumen environment and were related to changes in cell wall digestion. The activities were highly correlated with disappearance of DM and neutral-detergent fibre from nylon bags incubated in the rumen, rumen and total digestion of cell-wall carbohydrates and rumen pool size of cell-wall carbohydrates. It was concluded that the attachment of fibrinolytic enzymes is involved in the depression of fibre digestion. Particle-associated CMCase and xylanase activities were much higher when measured from rumen particulate material than from feed particles incubated in nylon bags.