Influence of dietary fibre on nutrient digestibility and energy utilisation in growing pigs fed diets varying in soluble and insoluble fibres from co-products

The co-products from the industry are used to reduce costs in pig diets. However, the co-products used in pig diets are limited because of a high fibre content which is not digested by endogenous enzymes and is resistant to degradation in the small and large intestines. The aim of this study was to investigate digestibility of nutrients and energy, and energy utilisation in pigs fed diets with various soluble and insoluble dietary fibre (DF) from co-products. The experiment was performed as a 4 × 4 Latin square design (four diets and four periods) using four growing pigs (66.2 ± 7.8 kg) surgically fitted with a T-cannula in the end of the small intestine. The pigs were fed four experimental diets: low-fibre control (LF), high-fibre control (HF), high-soluble fibre (HFS) and high-insoluble fibre (HFI) diets. The apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of ash, organic matter, CP, fat, carbohydrates, starch and non-starch polysaccharides (NSP) divided into cellulose and soluble and insoluble non-cellulosic polysaccharide residues were measured using chromic oxide as marker. The recovery of total solid materials, organic matter and total carbohydrates in ileal digesta in pigs fed the HF and HFS diets was higher than in pigs fed LF and HFI, whereas recovery of organic matter and total carbohydrates in faecal materials in the HFS diet was lowest (P < 0.05). AID of organic matter, total carbohydrates and starch was lowest for HFS diet (P < 0.05). ATTD of organic matter and CP was higher for LF diet compared with other diets (P < 0.05), whereas total NSP, cellulose and non-cellulosic polysaccharides residues were highest for HFS diet (P < 0.05). Lactic acid in ileal digesta was influenced by dietary composition (P < 0.05) whereas neither type nor level of DF affected short chain fatty acids. The digestible energy, metabolisable energy, net energy and retained energy intake were similar among diets without influence of DF inclusion (P > 0.05). The metabolisable energy:digestible energy ratio was lower when feeding the HFS diet because of a higher fermentative methane loss. Faecal nitrogen and carbon were positively correlated with DM intake and insoluble DF in the diets (P < 0.05), but nitrogen and carbon (% of intake) were similar among diets. The present findings suggest that high-DF co-products can be used as ingredients of pig diets when features of DF are considered.     

Predicting feed digestibility from NIRS analysis of pig faeces

Digestibility is a key parameter in the evaluation of feeds; however, the measurements on animals require heavy experimental trials, which are hardly feasible when large numbers of determinations are required – for example, in genetic studies. This experiment aimed at investigating the possibility to predict digestibility from NIRS spectra measured on faeces. A total of 196 samples were available from a digestibility experiment investigating the effects of age and genetic background of Large White pigs fed the same diet, rich in fibre (NDF=21.4% DM). Digestibility of dry matter (dDM), organic matter (dOM), nitrogen content (dN), energy (dE) and apparent digestible energy content (ADE) were calculated, as well as total N content of faeces (N). The faeces samples were submitted to reflectance NIRS analysis after freeze-drying and grinding. Calibration errors and validation errors were, respectively, 0.08 and 0.13% DM for total N in faeces, 0.97% and 1.08% for dDM, 0.79% and 1.04% for dOM, 1.04% and 1.47% for dN, 0.87% and 1.12% for dE and 167 and 213 kJ/kg DM for ADE. These results indicate that NIRS can account for digestibility differences due to animal factors, with an acceptable accuracy. NIRS appears to be a promising tool for large-scale evaluations of digestibility. It could also be used for the study of digestibility of different feeds, after appropriate calibration based on a wide range of feed types.     

An in vitro nutritive evaluation of olive tree (Olea europaea) pruning residues as affected by cutting regimen

Nutritive values of the branches from Olea europaea trees cut at 25, 50, 75 or 100 cm distance from the tip were evaluated by determination of the in vitro digestible organic matter (IVDOM), metabolizable energy (ME), net energy lactation (NEL), and presence nutritional and anti-nutritional components. The values of nutritive components, nitrogen forms, IVDOM, ME and NEL declined and concentrations of crude fiber and cell wall constituents increased with the increase in cutting length. Total phenols, hydrolysable tannins and condensed tannins amounted to 70, 17 and 0.6 g/kg DM, respectively. The addition of polyethylene glycol (PEG, 6000) to the plant samples incubated with rumen fluid at a ratio of (2:1 PEG:substrate) increased the values of IVDOM, ME and NEL by 40 g/kg DM, 0.59 MJ/kg DM and 0.42 MJ/kg DM, respectively. IVDOM, ME and NEL were negatively correlated with crude fiber and cell wall constituents but positively correlated with nitrogen forms and non-fiber carbohydrates. Olive pruning branches in diameter <3 mm could be used as sources of feeds for small ruminants.     

Effect of dehulling of rapeseed on feed value and nutrient digestibility of rape products in pigs

In the presented study the influence of dehulling rapeseed on the composition of rapeseed meal (RM) and rapeseed cake (RC) and on its feed value for piglets and growing-finishing pigs was investigated. Before withdrawal of oil, rapeseed (variety Express) was dehulled applying a procedure developed by SKET GmbH Magdeburg and the Section Food-Technology of the University Essen. The steps of the dehulling procedure were described. For RM the oil was removed by the prepress-solvent procedure till a crude fat content of 2.1% in DM. RC was produced by pressing only resulting approximately 13% crude fat in DM. The RM and RC from not dehulled (ND) and dehulled (D) rapeseed were examined analytically. Crude nutrients, sugar and fibre substances, amino acids, some minerals and trace elements, fatty acids, glucosinolates and sinapine, and phytate were determined. By dehulling the seed the crude fibre content was decreased in RM and RC by approximately 40%. The ADF content declined by 35 and 39%, and the NDF content by 28% and 40% in RM and RC, respectively. The decrease in ADL content amounted to 50% and 65% for RM and RC, respectively. On the other hand, the CP content of RM and RC was increased by 7% and 13%, respectively, by dehulling the seed while the amino acid content of rape protein increased only slightly. The contents of glucosinolates and sinapine were also increased by dehulling, while the contents of phytate and phytate P were decreased. In digestibility and balance experiments with piglets and intact hybrid breeds of growing-finishing pigs, the digestibility of organic matter and of crude nutrients and the contents of digestible energy and metabolizable energy were estimated. Furthermore, the precaecal digestibility of crude nutrients and amino acids was determined with fistulated mini-pigs. By dehulling the seeds the digestibility of organic matter from RM and RC was improved in piglets and adult pigs by approximately 10%, and the ME contents increased by 13-15%. The precaecal digestibility of the sum of amino acids was increased by approximately 3 and 6 units in RM and RC, respectively. The precaecal digestibility of lysine in RM and RC reached that of soybean oil meal from not dehulled beans.     

Apparent and true digestibility of the Weende components, cell content and cell wall of ryegrass

For 14 samples of ventilated hay and 6 of fresh grass, digestibility was determined with young wethers. The contribution to the digestibility was calculated for the Weende components (crude protein, crude fibre, nitrogen-free extractives + fat) and for cell content and cell wall (Van Soest) components. For the cell content and crude protein, a hyperbolic relationship, y' = a − b/x between the digestibility coefficient of the components (y') and the percentage component in dry matter (DM, x) can be accepted with a sufficient degree of certainty. This means that the apparent digestibility of the cell content and crude protein increase with increasing concentration. The latter formula can be transformed into a linear regression y = ax − b where y = percentage digestible component in DM, a being an estimate of the true digestibility of the component and b an estimate of the endogenous excretion of the component. From these relationships some important practical conclusions can be drawn. For other dry matter components, such as crude fibre, nitrogen free extractives + fat and cell wall, the relationship between the digestibility coefficient and the percentage of the component in DM cannot be expressed by a simple regression line. The advantages of splitting the digestibility into a contribution from cell content and cell wall components versus splitting into contributions from the Weende components are discussed.By determination of the cell wall and its digestibility in vitro, a very good prediction for the dry matter digestibility of grass can be given, which is of great importance for plant breeding and grassland research.     

The nutritional value for sheep of molasses and condensed molasses solubles

The nutritional value of cane molasses and condensed molasses solubles (CMS, a highnitrogen by-product from the fermentation of beet molasses) was studied in two metabolism experiments with sheep.Nitrogen balance and the apparent digestibility of dry matter, organic matter, ether extract and acid detergent fibre in a barley-based control diet were not affected when 10 or 20% barley dry matter was replaced by either molasses or CMS dry matter. The digestibility of crude protein was significantly increased by CMS, because it increased the crude protein content of the rations. There was a positive linear relationship between crude protein and digestible protein as a percentage of the dry matter. The digestibility of nitrogen-free extract was depressed by the inclusion of molasses or CMS. Digestibility of energy was not significantly influenced by the inclusion of molasses at 10 or 20% or CMS at 10% but was depressed by the inclusion of CMS at 20%. The digestible energy of molasses was 82% of that of barley and the digestible energy of CMS was 84% of that of molasses.The extent of fermentation of ration components was studied in sheep with rumen and duodenal re-entrant cannulae. Although the apparent digestibility of dry matter, organic matter and gross energy was not affected by 20% molasses or CMS, the concentration of butyric acid in the rumen liquor was significantly increased at the expense of propionic acid. The concentration of ammonia in the rumen was elevated by high nitrogen intake. High concentrations of ammonia in the rumen liquor caused proportional excretion of nitrogen in urine.     

Effects of fibre-degrading enzymes in combination with different fibre sources on ileal and total tract nutrient digestibility and fermentation products in pigs

ABSTRACT

The study was conducted to determine effects of a complex of fibre-degrading enzymes (xylanase, cellulase and β-glucanase) on nutrient digestibility, fibre fermentation and concentrations of short chain fatty acids (SCFA) at different parts of digestive tract in pigs fed different fibre-rich ingredients. A total of 36 barrows fitted with T-cannulas in the distal ileum (initial body weight of 41.1 ± 2.7 kg) were randomly allotted to six dietary treatments with three different high-fibre diets including maize bran (MB), sugar beet pulp (SBP) and soybean hulls (SH) with or without supplementation of fibre-degrading enzymes. Enzyme supplementation improved (p < 0.05) apparent ileal digestibility (AID) of dietary gross energy (GE), crude protein, dry matter (DM), organic matter (OM), total dietary fibre (TDF), neutral detergent fibre (NDF) and apparent total tract digestibility (ATTD) of dietary GE, DM, OM, TDF, insoluble dietary fibre (IDF) when pigs were fed MB, SBP or SH diets. When compared to the SBP and SH diets, the AID of GE, DM, ash, OM and NDF in diet MB was higher (p < 0.05), but the hindgut disappearance and ATTD of nutrients, except for ether extract and crude ash, were lower (p < 0.05). Enzyme supplementation increased acetate and total SCFA concentrations in ileal digesta and faeces of pigs. In conclusion, enzyme addition improved IDF fermentation and SCFA concentration in the whole intestine of pigs, and there was a large variation of digestibility of fibre components among MB, SH and SBP owing to their different fibre composition. Therefore, fibre-degrading enzymes should be applied to fibrous diets to improve efficient production of swine, especially considering low fibre digestibility of fibre-rich ingredients.     

The digestive strategy and efficiency of the West Indian manatee, Trichechus manatus

During the winters of 1982/83 and 1983/84, samples of digesta were collected from nine sites along the gastrointestinal tracts of seven West Indian manatees, Trichechus manatus. The voluminous large intestine of the manatee is responsible for considerable water reabsorption, as well as being the major site of organic matter, nitrogen and crude fat digestion. Cellulose digestion occurs primarily in the cecum and anterior portion of the colon in a pattern similar to terrestrial nonruminant herbivores like the horse. Overall digestibility coefficients for organic matter (71%), nitrogen (61%) and crude fat (77%) are comparable to those of terrestrial herbivores. Manatees have one of the highest digestibility coefficients for cellulose (80%) of any known mammalian herbivore. This high efficiency of cellulose digestion is due primarily to an extremely slow rate of passage. In addition, it appears that seagrasses may be more digestible than terrestrial forages, possibly due to their relatively low lignin content.     

Digestibility of wet cage layer excreta and an excreta-supplemented diet by cattle as determined by two methods

Digestibility studies were carried out with cattle to determine coefficients of digestibility for residual nutrients in wet cage layer excreta (CLE), and the effect of incorporating CLE in a maize silage-based diet, on nutrient digestibility. Two methods were used and compared — total collection, and the use of the recently identified internal marker, acid insoluble ash (AIASH).Digestibility coefficients for cage layer excreta were: dry matter, 74.0; organic matter, 73.1; crude protein, 76.8; energy 71.3; acid detergent fibre, 71.8%. Substituting CLE for soya bean meal or urea in the maize silage-based diet did not adversely affect nutrient digestibility. Comparable digestion coefficients were obtained with both the total collection method and the AIASH marker technique, confirming the results of others that the AIASH marker gives satisfactory estimates of nutrient digestibility.     

Measurement and prediction of digestibility of forage maize in The Netherlands

Results of digestibility trials on fresh and ensiled maize (aerial parts) were analysed and compared with laboratory data.

Digestibility of the organic matter of ears was almost constant at 84–85%. Digestibility of organic matter of stover showed great variation. Variation between animals in apparent digestibility of organic matter was greater for maize diets than for diets based on grass products. Most of the differences between animals were caused by differences in the digestion of cell walls. When the true digestibility of cell contents was assumed to be complete, endogenous excretion was, on average, only 7% with respect to organic matter intake, and seemed dependent on digestibility of organic matter.

Prediction of apparent digestibility was more accurate with digestibility in vitro than with crude fibre, although for maize silage, significant relationships were found between crude fibre content and digestibility of organic matter. Standard deviation of organic matter digestibility between lots of fresh and ensiled maize grown on commercial farms amounted to only about 1.2 –2%. As this was only twice the accuracy of digestibility in vivo with four animals, fixed values will be presented to farmers, possibly corrected for year, hybrid selection and cropping practice.     

Influence of dietary fibre level and pelleting on the digestibility of energy and nutrients in growing pigs and adult sows

Two experiments were carried out to investigate the effect of pelleting on the apparent total tract digestibility (ATTD) of energy and nutrients according to the dietary fibre (DF) level in growing pigs (experiment 1) and in adult sows (experiment 2). Four diets based on wheat, barley, maize and soybean meal and supplemented with increased contents of a mixture of wheat bran, maize bran, soybean hulls and sugar beet pulp (116, 192, 268 and 344 g NDF/kg dry matter (DM) in diets 1 to 4) were tested. In experiment 1, 32 growing pigs (62 kg average BW), in two replicates and according to a factorial design, were fed one of the four diets, either as mash or as pellets. The digestibility of energy, organic matter (OM) and all nutrients decreased with DF increasing for both feed forms; the reduction was about 1% for each 1% NDF increase in the diet (P < 0.001). Pelleting improved moderately the digestibility of energy and OM (+1.5% and +1.0%, respectively; P < 0.05) in connection with greater DF (+5%; P < 0.05) and fat digestibility (+25%). Thus, pelleting improved the digestible energy content of diets on average by 0.3 MJ/kg of feed DM (P < 0.01). In experiment 2, four adult dry sows (235 kg average BW) were used in a 4 × 4 Latin square design and fed the four diets used in experiment 1 as pellets. The digestibility of energy, OM and macronutrients also decreased with DF increase (P < 0.001; -0.4% per 1% increase of dietary NDF for energy) while the digestibility of DF (i.e. crude fibre (CF) or ADF) increased (P < 0.001) or remained at a high level. In conclusion, increasing DF in diets decreases the digestibility of nutrients and energy in pigs and in sows. Although positive, the pelleting impact is minor on the energy and nutrients digestibility of fibre-rich diets in growing pigs, even in high-DF diets.     

Use of the mobile nylon bag technique to determine the digestible energy content of traditional and non-traditional feeds for swine

The following experiment was conducted using the mobile nylon bag technique (MNBT) to determine dry matter and energy digestibility in traditional feeds as well as non-traditional feeds in order to calculate digestible energy (DE) values for use in ration formulation programmes. A total of 22 ingredients were tested in this experiment including the traditional cereal grains barley, corn, oats and wheat, as well as secondary cereal grains such as normal and low viscosity rye, low lignin and high fat oat groats, wheat heavies and # 1 wheat screenings and a new bread wheat designated as CDC Teal. Three legumes (lupines, peas and dehydrated alfalfa), three varieties of canary seed (CDC Maria, dehulled CDC Maria and Keet), and raw and micronized canola seed were tested as protein sources. Finally, three oilseed meals obtained from the Chinese feed industry (Chinese rapeseed meal, Chinese cottonseed meal and extruded full-fat soybean meal) were also included. After simulating gastric digestion the nylon bags were inserted into the duodenum of five barrows through simple duodenal T-cannulae. Eight bags were administered to each pig daily. Ten nylon bags were prepared for each feed with two bags being inserted into each of the five barrows. A total of 220 bags were inserted over a 7-day period. The overall results of this experiment indicate that the MNBT has great potential for use in determining the digestible energy content of swine feeds. For the most part, values obtained in the present experiment compared favourably with previously published values. Four feedstuffs produced digestible energy values that differed by greater than 5% from previously reported values. However, variation in chemical content provided a reasonable explanation for these discrepancies. The MNBT has several advantages compared with conventional digestibility methods in that many feeds can be tested in a relatively short duration of time with significantly fewer animals being used, only small amounts of feed are required and the test allows for energy measurements in feedstuffs that would not normally be fed to pigs as a single ingredient. Additional research on a wider variety of feedstuffs should be conducted to confirm the potential of the MNBT as a tool to accurately determine DE values for swine.     

A simple, integrative assay to quantify nutritional quality of browses for herbivores

Many regard the concentrations of nitrogen (N), tannins and plant cell wall constituents (fibre) as key indicators of food quality and habitat suitability for browsing herbivores; yet there is no method for measuring their combined effects. We have developed a simple in vitro assay for measuring the effects of tannins and fibre on N availability in browse. We determined the effects of tannins by measuring the polyethylene glycol (PEG)-binding capacity (PEG-BC) of Eucalyptus leaf samples, followed by a two-stage in vitro digestion with pepsin and cellulase to determine the digestibility of dry matter and N. There was a significant relationship between concentrations of digestible N and the PEG-BC of the leaves. Furthermore, adding PEG significantly improved the digestibility of N. Our results concur with in vivo observations from several mammalian species. This suggests that our method is effective for measuring the nutritional quality of browse and the benefits of adding PEG, providing some index of the detrimental effects of tannins. We further simplified the assay by removing the PEG step, allowing us to quickly analyse samples in bulk. Nevertheless, this simplified method is still not practical for analysing the many samples necessary to compare the nutritional values of different tracts of forest. We used near-infrared reflectance spectroscopy to produce calibration equations and predicted total and digestible N in 322 trees at eleven sites. Both within and between sites, we found a wide variation in concentrations of digestible N but a much lower variation in total N, with either no relationship or poor relationships between the two measures. This confirms the variability in the nutritional quality of eucalypt forests, which may explain the distribution and abundance of mammalian herbivores. Thus, our assay provides a useful tool for understanding how food resources influence herbivore populations at different scales. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effect of ambient temperature on nutrient digestibility and nitrogen balance in sheep fed brown-midrib maize silage

The aim of the experiment was to determine the impact of heat stress on nutrient digestibility and nitrogen balance in sheep fed silages differing in fibre quality. The digestibility trial was conducted at three different ambient temperatures (15°C, 25°C and 35°C for 24 h/d). The tested brown-midrib maize (Bm) silage had a higher nutrient digestibility, except for ether extract (EE) and a higher metabolisable energy (ME) content than the control maize (Con) silage. Nitrogen (N) excretion with faeces was higher but N excretion with urine was lower for sheep fed Bm silage, subsequently N balance did not differ between the two silages. Temperature had no effect on nutrient digestibility, except for crude protein (CP), but N excretion with urine was lower at elevated temperatures. A diet by temperature interaction was found for dry matter (DM) and organic matter (OM) digestibility. When the ambient temperature increased from 15°C to 25°C, the DM and OM digestibility increased in animals fed Con silage, but decreased in animals fed Bm silage. Concomitantly, ME estimated from digestible nutrients was higher for Bm than for Con at 15°C, but no differences were found at 25°C and 35°C. Effects of diet by temperature interaction, furthermore, were observed for EE and CP digestibility. Therefore, forage quality has to be considered when feeding heat-stressed animals.     

Nutrient digestibility and prediction of metabolizable energy in total mixed rations for ruminants

The aim of the present study was to determine equations that predict ME in total mixed rations (TMR) based on routine methods. The ME content of 30 TMR for dairy cows was determined based on digestible crude nutrients obtained with wether sheep. Concentrations in the TMR (in g/kg DM) varied between 118 and 234 for crude protein, 26 and 48 for crude lipid, 131 and 250 for crude fibre, 281 and 488 for NDF, and 173 and 304 for ADF. Gas production ranged from 40.7 to 54.1 ml/200 mg DM, and enzymatically degraded organic matter from 652 to 800 g/kg DM. Digestibility [%] ranged from 68.6 to 84.0 for organic matter, from 55.6 to 84.3 for crude lipid, from 55.0 to 77.8 for crude fibre, from 57.6 to 77.0 for NDF and from 53.1 to 79.6 for ADF. ME ranged from 9.6 to 11.9 MJ/kg DM, and NEL from 5.7 to 7.4 MJ/kg DM. ME content was highly correlated with the concentration of both crude fibre and enzymatically degradable organic matter as well as with organic matter digestibility. A multiple regression equation based on crude fibre and crude lipid predicted ME with a reasonable goodness of fit (r² = 0.81; s_y.x = 2.4%). The inclusion of other nutrients, of neutral and acid detergent fibre, neither of gas production did improve the goodness of fit. The best prediction was achieved with inclusion of enzymatically degraded organic matter (r² = 0.90; s_y.x = 1.7%).     

A simple enzyme assay for dry matter digestibility and its value in studying food selection by generalist herbivores

Summary The dry matter digestibility of 94 species of leaf was assayed by a simple method involving sequential treatment with pepsin and fungal cellulase enzymes. It was demonstrated that for foliage from rainforest trees of a wide range of dicotyledonous plant families the assay showed high positive correlation with estimates of dry matter digestibility obtained using rumenliquor from a fistulated steer. Both assays were found to reflect negative correlates of digestibility, notably fibre and condensed tannin, rather than the nutritional value of an item. The higher dry matter digestibility of immature leaves relative to mature leaves appeared to be accounted for by their lower fibre content. It is suggested that the pepsin/cellulase assay offers a cheap, quick, routine method of gaining information on the effects of some types of plant secondary compounds (digestibility reducers) on the food potential of different kinds of foliage to herbivores. Its use in studies of herbivory in rainforest areas in relation to analyses for plant secondary compounds and food selection by herbivores is discussed.Publication 20-018 of the Wisconsin Regional Primate Research Center     

Effects of dietary cellulase and xylanase addition on digestion,rumen fermentation and methane emission in growing goats

The objective of this study was to evaluate the effectiveness of supplementation of cellulase and xylanase to diets of growing goats to improve nutrient digestibility, utilisation of energy and mitigation of enteric methane emissions. The experiment was conducted in a 5 × 5 Latin square design using five goats with permanent rumen fistulae and five treatments consisted of two levels of cellulase crossed over with two levels of xylanase plus unsupplemented Control. The cellulase (243 U/g) derived from Neocallimastix patriciarum was added at 0.8 and 1.6 g/kg dry matter intake (DMI) and the xylanase (31,457 U/ml) derived from Aspergillus oryzae was fed at 1.4 and 2.2 ml/kg DMI. There were no differences in apparent digestibility of organic matter, neutral detergent fibre, acid detergent fibre and rumen fermentation parameters (i.e. ammonia-nitrogen [N], volatile fatty acids) among all treatments. Dietary cellulase and xylanase addition did not influence energy and N utilisation. But compared to xylanase addition at the higher dose, at the low xylanase dose the retained N, the availability of retained N and digested N were increased (p < 0.01). Moreover, enzyme addition did not affect the enteric methane emission and community diversity of ruminal methanogens. The present results indicated that previous in vitro findings were not confirmed in ruminant trials.     

Foraging strategy of cattle in patchy grassland

We tested several strategies of foraging that grazing herbivores may adopt in a patchy habitat in relation to energy intake. The patch selection of cattle was investigated in an Agrostis/Festuca grassland and in a Lolium grassland in 13 observation periods over 2 years. Both grasslands were stocked with five yearling steers. Bite counts were made on patches of different vegetation structure: short, tall and mature stemmy grass. Bite size of each patch category was determined by hand-plucking. Samples of patch types were analysed for organic matter digestibility, as a measure of energy content. There was a large seasonal variation in relative patch cover and in forage characteristics. However, the differences between patches in bite size, bite rate and digestibility were consistent over time. In short patches digestibility was high, bite size was low and bite rate was high compared to stemmy patches. In tall patches digestibility was only little lower than in short patches and bite size and bite rate were intermediate between short and stemmy patches. The steers selected the short and tall patches over the stemmy patches, despite a relatively low intake rate of digestible organic matter in the short patches. Four hypotheses on foraging strategy were examined to explain the allocation of time or bites between patches: random allocation according to bites, random allocation according to grazing time, matching of time in proportion to digestibility, and matching of time in proportion to intake rate of digestible organic matter. The observed distribution of bites and time between patches was significantly different from the predictions of the various hypotheses. Patch choice was better explained by a random allocation of grazing time than by a random allocation of bites. Matching for digestible organic matter intake rate yielded the worst predictions of patch selection. Matching for digestibility gave the best explanation of patch selection, but the improvement compared to a random allocation of grazing time was not significant. The significance of the contribution of digestibility to selection may have been confounded by the effect of increased selectivity within tall patches. Observed patch selection was considered in relation to the maximization of energy intake rate. The selectivity of cattle was not pronounced, but it was consistent with a principle of maximization of energy intake on a daily basis instead of a short-term basis. Selectivity appeared to be constrained by costs of searching for and discriminating between different forage resources. It is concluded that a flexible selection for short patches over tall patches and avoidance of stemmy patches provides a good approximation of energy intake maximization in a complex and changing environment.     

Effect of chemical treatments on the degradability of cotton straw by rumen microorganisms and by fungal cellulase

Three different chemical treatments—sulfur dioxide, ozone, and sodium hydroxide—were applied on cotton straw, and the effect on cell-wall degradability was assessed by using rumen microorganism and Trichoderma reesei cellulase. Sulfur dioxide (applied at 70°C for 72 h) did not change the lignin content of cotton straw but reduced the concentration of hemicellulose by 48%. Ozone exerted a dual effect, both on lignin (a 40% reduction) and hemicellulose (a 54% decrease). The treatment with NaOH did not solublize cell-wall components. The in vitro organic matter digestibility with rumen fluid of cotton straw was increased significantly by ozone and SO₂ treatments, by 120% and 50%, respectively, but not by NaOH. T. reesei cellulase was applied on the chemically pretreated cotton straw at a low level (6 filter paper U/g straw, organic matter), and the release of reducing sugars was determined. The highest level of reducing sugars (30.6 g/100 g organic matter) was obtained with the O₃-cellulase combination, which solubilized 64% of the cellulose and 88% of the hemicellulose. the SO₂- and the NaOH-pretreated cotton straw were hydrolyzed by T. reesei cellulase to the same extent (21 g reducing sugars/100 g organic matter). The rumen fluid digestibility of the enzymatic ally hydrolyzed straw was not increased further over the effect already obtained with the chemical pretreatments. However, the fermentability of the combined treatments was increased markedly. In the O₃-cellulase-treated cotton straw, 83% of the rumen fluid digestible material consisted of highly fermentable components. Although ozone proved to be the most potent pretreatment for enzymic saccharification in this study, the absolute result was modest. The limited effect of the combined O₃-cellulase treatment was probably associated with the pretreatment limitations, but not with the enzyme level. Based on the differential response of the chemically treated cotton straw to attack by rumen microorganisms on the one hand, and by T. reesei cellulase on the other hand, a hypothesis has been suggested as to the location of lignin and hemicellulose in the cellwall unit of cotton straw.     

Production of volatile fatty acids from bagasse by rumen bacteria

Summary Conditions are described for converting bagasse lignocellulose to volatile fatty acids (VFA) by anaerobic fermentation. Although yields of VFA were as high as 74% by weight of digestible organic matter (or 54% of dry bagasse), limitations were imposed by both fermenter design and fibre digestibility. All fermentations were substrate-limited up to the maximum initial concentration examined of 50 g bagasse · l^-1 and no product inhibition was evident (up to 260 mM VFA produced). Maximum VFA productivities of 0.25 to 0.65 g · l^-1 · h^-1 were obtained in batch fermentations and this is greater than those previously reported using lignocellulosic substrates. Batch fermentations neared completion after 66 h.