More efficient mastication allows increasing intake without compromising digestibility or necessitating a larger gut: Comparative feeding trials in banteng (Bos javanicus) and pygmy hippopotamus (Hexaprotodon liberiensis)

The digestion of plant material in mammalian herbivores basically depends on the chemical and structural composition of the diet, the mean particle size to which the forage is processed, and the ingesta retention time. These different factors can be influenced by the animal, and they can presumably compensate for each other. The pygmy hippopotamus, a non-ruminating foregut fermenter, has longer mean retention times than ruminants; however hippos do not achieve higher (fibre) digestibilities on comparable diets, which could be due to ineffective mastication. We performed feeding trials with six pygmy hippos (Hexaprotodon liberiensis) and six banteng cattle (Bos javanicus) on a grass diet. As predicted, both species achieved similar dry matter, organic matter, crude protein and gross energy digestibilities. However, neutral and acid detergent fibre digestibility was lower in pygmy hippos. Apparently, in these species, fibre digestibility was more influenced by particle size, which was larger in pygmy hippos compared to banteng, than by retention time. In spite of their higher relative food intake, the banteng in this study did not have greater relative gut fills than the hippos. Ruminants traditionally appear intake-limited when compared to equids, because feed particles above a certain size cannot leave the rumen. But when compared to nonruminating foregut fermenters, rumination seems to free foregut fermenters from an intrinsic food intake limitation. The higher energy intakes and metabolic rates in wild cattle compared to hippos could have life-history consequences, such as a higher relative reproductive rate.     

On the relationship between chitin particle size and digestibility in the primate Galago senegalensis

Experiments were performed to examine the relationship between the particle size of chitin and its digestibility in the small insectivorous prosimian Galago senegalensis. In the first set of experiments, four animals were fed a 25% chitin diet with the chitin particles less than or equal to 60-mesh (0.250 mm maximum diameter). On average, the animals digested 22.5 ± 2.2 percent of the ingested chitin. In the second set of experiments, the four animals were fed a 25% chitin diet with the chitin particles ground to ≤ 40- and ≥ 45-mesh (between 0.425 and 0.325 mm). On average, the animals digested 2.75 ± 1.38 percent of the ingested chitin. There was no significant variation between the performance of any of the animals on either the 60- or 40–45-mesh trials. In all instances, however, each animal digested significantly more of the 60-mesh chitin and the 40–45-mesh chitin. These experiments demonstrate the importance of masticatory efficiency among small mammals for improving the digestibility of foods such as insects which contain high proportions of chitin. They also suggest why insectivorous and folivorous primates have certain convergent dental specializations for finely grinding their foods. Both leaves and insects contain relatively indigestible structural carbohydrates. These substances are much more completely digested when the surface area to volume ratio of the swallowed material is increased. The masticatory efficiency of frugivorous primates is much lower since the constituents of these foods are relatively completely digested irrespective of the fineness of grinding.     

Fluid and particle retention in captive okapi (Okapia johnstoni)

Retention time of food in the digestive tract is among the key variables that describe the digestive strategy of a herbivore. Mean retention time (MRT) was measured on 4 captive specimens of the okapi, a strictly browsing ruminant. Retention time was quantified on different diets, using Co-EDTA (fluid phase) and Cr-mordanted fibres (1–2 mm) (particle phase) as pulse-fed markers. Average food intake was 55–65 g DM/(kg BW^0.75*d). Fecal excretion of the markers was quantified over 10 days. Different models to calculate retention time and passage rate in the gastrointestinal tract (GIT) and the reticulorumen (RR) were applied. Average MRT_particleGIT was quantified to be 47 ± 8 h and MRT_fluidGIT 36 ± 5 h. Concerning estimation of retention times in the reticulorumen, MRT_particleRR was quantified to be 27 ± 7 h, while MRT_fluidRR was 17 ± 4 h. The quotients MRT_particle/MRT_fluid were quantified to be 1.3 ± 0.1 for the GIT and 1.6 ± 0.2 for the RR. Compared to data established with comparable markers, the okapi has low coefficients of MRT_particle/MRT_fluid. A less well developed retention mechanism for fibres compared to species like cattle or sheep can be explained by a comparatively high fermentation rate and low digestibility of the natural food of the okapi—browse—in comparison to grass.     

Differences in mean retention time of sheep and goats under controlled feeding practices

The objective of this study was to compare the mean retention time (MRT): (a) between sheep and goats when they fed in groups with the same diet, the same amount of food and forage to concentrate (F/C) ratio and (b) between group and individual feeding in each animal specie (the same diet, the same amount of food and F/C ratio). Twelve, 3-4 years old, Friesian crossed dairy ewes and twelve, 3-5 years old, Alpine crossed dairy goats were used for the experiment. The animals were fed with a diet, consisted of alfalfa hay, wheat straw and concentrate, in two treatments. In Treatment A the animals fed on a group basis as it is traditionally used in practise, while in Treatment B the diet was offered individually toin each animal, in order to have fully comparable feeding level among animals and between treatments. Each Treatment (A and B) lasted 3 weeks. The results of this study have shown that: sheep had significantly longer rumen retention time (RRT) (30.03 vs. 14.43) and mean retention time (MRT) (40.80 vs. 27.81), and shorter transit time (TT) (8.86 vs. 11.49) than goats, while the caecum retention time (CRT) did not differ between the two species in Treatment A (group feeding). The comparison between group (Treatment A) and individual feeding (Treatment B) in goats or in sheep has shown that there were no significant differences as RRT, CRT, TT and MRT concerns. In conclusion, animal species (sheep vs. goat) was the main factor which affected the MRT, RRT and TT when the animals were fed in groups with the same diet, amount of food and F/C ratio, while the feeding technique (group vs. individual) had no effect on those parameters in both animal species.     

Nitrogen content, amino acid composition and digestibility of fungi from a nutritional perspective in animal mycophagy

Fungi comprise a major part of the diet of many animals. Even so, the nutritional value of fungi has been much debated, with some arguing that fungi are nutritionally poor. However, the chemical composition of fungi and of the biology of the animals that eat them are not well understood, particularly in reference to amino acid (AA) composition of fungi and digestibility of fungal protein. We analysed fibre, total nitrogen (N), available N, and AA contents and measured in vitro digestibility of a wide range of epigeous and hypogeous fungi collected in Australia and the USA to test three hypotheses: (i) fungi are nutritionally poor because they contain few nutrients or are otherwise of low digestibility, (ii) fungi vary substantially in their nutritional composition; and (iii) animals can counter this variable quality by eating diverse taxa. Resultant data indicate many fungi are a reasonable source of AAs and digestible nitrogen. However, they vary highly between species in AA content, and the protein has a poor balance of digestible AAs. This helps explain why many mycophagous animals eat a wide array of fungi and often have digestive strategies to cope with fungi, such as foregut fermentation. Another common strategy is to supplement the diet with high quality protein, such as insect protein. Accordingly, evaluating nutritional value of fungi requires consideration of physiology of the animal species and their whole diet.     

Digestive performance and selective digesta retention in the long-nosed bandicoot,Perameles nasuta,a small omnivorous marsupial

Bandicoots are opportunistic omnivores that feed on invertebrates, fungi and both epigeal and hypogeal plant parts. We examined the performance of the digestive tract of the long-nosed bandicoot (Perameles nasuta) in terms of intake and total digestibility, patterns of excretion of inert digesta markers, and likely sites of digesta retention, on two diets designed to mimic part of their natural plant and insect diets. On the insect diet (mealworm larvae), bandicoots virtually maintained body mass at a digestible energy intake of 511 kJ · kg^-0.75 · day^-1 and were in strongly positive nitrogen balance. In contrast, on the plant diet (shredded sweet potato), bandicoots ate only one-third as much digestible energy, lost 7% body mass, and were in negative nitrogen balance. Mean retention times of two particle markers on the plant diet (27.5 and 27.0 h) were more than double those on the insect diet (12.4 and 11.2 h), and on both diets the mean retention time of the fluid digesta marker was greater than those of the particle markers, indicating consistent selective retention of fluid digesta in the gut. It was seen radiographically than in mealwormfed bandicoots major sites of digesta retention were the distal colon and rectum, whereas in the sweet potato-fed animals the caecum and proximal colon were principal sites. It was concluded that retention of plant material in the caecum and proximal colon (the main sites of microbial digestion) and the preferential retention of fluid digesta (together with bacteria and small feed particles) in the caecum were important factors in the ability of bandicoots to switch between insect and plant foods, depending on relative availabilities, and thus to exploit nutritionally unpredictable environments.Abbreviations ADF acid-detergent fibre - bm body mass - Co-ED-TA cobalt-ethylenediaminetetra-acetic acid - CWC cell wall constituents - DE digestable energy - dm dry matter - EUN endogenous urinary nitrogen - ICP inductively-coupled plasma atomic emission spectroscopy - MFN metabolic faecal nitrogen - MRT mean retention time - NDF neutral-detergent fibre - ww wet weight     

The dissociation of the fluid and particle phase in the forestomach as a physiological characteristic of large grazing ruminants: an evaluation of available, comparable ruminant passage data

Whether differences in digestive physiology exist between different ruminant feeding types has been an ongoing debate. In this regard, potential differences in ingesta retention have been understood to be of particular importance. We analyzed a data pool in which only mean retention time (MRT) data for the ruminoreticulum (RR) were collated that were obtained using comparable techniques with either chromium or cobalt EDTA as a fluid marker and/or with chromium-mordanted fiber of less than 2 mm in size as a particle marker. Data were compared using one averaged value per species. In general, the paucity of species in such a collection is striking and does not allow—in contrast to earlier statements—any final conclusions regarding the influence of body weight (BW) or feeding type on ruminant MRTs. In particular, there was no significant correlation between MRT_particlesRR or MRT_fluidRR and BW, neither in the interspecific nor in the intraspecific comparisons, and no difference between the feeding types. The trend that indicates longer MRT_particlesRR in grazers is based on too few species to be conclusive. Small browsers seemed to have shorter MRT_fluidRR than similar-sized grazers. In contrast, there was a trend for large grazers to have shorter MRT_fluidRR than large browsers. In direct pair-wise comparisons between cattle and the browsers giraffe, moose, and okapi, the latter difference was significant. Cattle also had the highest relative RR fluid outflow rates among the species investigated. This is in accord with the observation that grazers have larger omasa, a major function of which is water-reabsorption distal to the RR. Grazers seem to have longer MRT_particlesRR per unit MRT_fluidRR, and cattle are particular outliers in this respect. It is hypothesized that potentially shorter MRT_fluidRR in large grazers and higher relative outflow rates are linked to a higher saliva production and a lesser viscosity of both saliva and RR fluids. A constant supply of a fluid phase of low viscosity is proposed to be the prerogative for the physical mechanisms of flotation and sedimentation that result in the stratification of RR contents and its selective particle retention typical for large grazing species.     

No distinct stratification of ingesta particles and no distinct moisture gradient in the fore-stomach of non-ruminants: The wallaby,peccary, hippopotamus,and sloth

Herbivores that digest plant material in the fore-stomach can be divided in ruminants and non-ruminants. This study describes the distribution of feed particles (and inorganic material) and dry matter (DM) in the digestive tract of non-ruminant foregut fermenters. Results from passage trials led us to hypothesize that specific particle-sorting mechanisms, as observed in ruminants, are unlikely in non-ruminants. Therefore, no systematic particle size distribution effects (indicative of a sorting mechanism) should be evident in the fore-stomachs of these animals, but differences in fluid and particle retention suggest that differences in fluid concentration (measured as DM) could occur in the foregut of macropods and hippos. The gut content of eleven Bennett's wallabies (Macropus rufogriseus), six collared peccaries (Pecari tajacu), three pygmy hippos (Hexaprotodon liberiensis), two common hippos (Hippopotamus amphibius) and one two-toed sloth (Choloepus didactylus) were analyzed with an emphasis on the fore-stomach. The ventral and dorsal regions in sacciform compartments, and peripheral and central regions in tubular compartments, were examined. Results were not uniform across the species studied. A potential sedimentation mechanism was observed firstly by the accumulation of sand in the fore-stomach of the peccary and sloth, and secondly by the lower DM content in peripheral versus central and ventral versus dorsal regions of the fore-stomach of the wallabies and common hippos, respectively. However, pair-comparisons for different gut regions of wallabies and peccaries yielded no differences in mean particle size between fore-stomach regions. To conclude, some digesta fractionation does occur in the fore-stomach of the studied groups of non-ruminants, but not in a uniform manner, which in turn is in accordance with morphological dissimilarities of their respective foregut structures. The absence of systematic fractionation effects in non-ruminant foregut fermenters emphasizes the innovative character of the sorting mechanism in ruminants.     

Responses of the digestive tract of the omnivorous northern brown bandicoot, Isoodon macrourus (Marsupialia: Peramelidae), to plant- and insect-containing diets

The gastrointestinal tract of omnivores such as bandicoots (Marsupialia: Peramelidae) must be able to process foods as different as invertebrates, fungi and plant material. We studied the mechanisms involved in the utilisation by captive northern brown bandicoots (Isoodon macrourus) of insect larvae and milled lucerne (Medicago sativa) hay incorporated into a basal diet of a commercial small carnivore mix. Animals on the plant-basal mix digested less dry matter, energy, lipid, fibre and total nitrogen, but consumed 79% more dry matter than those on the insect-basal mix. Consequently intake of digestible energy (i.e. energy absorbed) was not significantly different between diets. Mean retention time (MRT, the mean time a marker remains in the tract) of a large particle marker was shorter on the plant-basal mix, reflecting its higher intake, but MRT of a solute marker was not significantly different between diets. Consequently the solute marker was retained longer than the particle marker on the plant-basal mix, indicating selective retention of solutes and very small particles in the caecum on this diet. This was confirmed by a higher proportion of small particles in the caecum than the distal colon of road-killed I. macrourus. Thus the main responses by I. macrourus to the plant-basal mix appeared to be an increase in gastrointestinal tract capacity (from radiographic evidence), selective retention of solutes and very small particles in the caecum, and facilitated passage of less tractable large particles through the colon. As a consequence, food intake was higher on the plant-basal mix, which compensated for its lower digestibility, and intake of digestible energy was similar to that on the insect-basal mix. This considerable flexibility of the morphologically rather simple digestive tract of northern brown bandicoots helps to explain their ability to cope with naturally variable diets consisting of mainly invertebrates in summer to much more plant and fungal material in winter, and to survive in nutritionally dynamic environments such as heathlands where there can be dramatic changes in food type and availability following periodic wildfires. Accepted: 14 April 1999     

Digestive performance and digesta passage in the omnivorous greater bilby, Macrotis lagotis (Marsupialia: Peramelidae)

Omnivores such as the greater bilby (Macrotis lagotis) consume a variety of dietary items and often are faced with large changes in the nutrient composition of their food. This paper explores the basis for the dietary flexibility of the bilby by comparing digestive performance and digesta retention patterns of captive bilbies fed either an insect diet (mealworm larvae) or a plant diet (mixed seeds). Mean retention times (MRTs) of particle and solute markers in the gastrointestinal tract did not differ significantly between the two diets, but MRT of the particle marker was significantly longer than that of the solute marker on both the mealworm (particle: 23.5 h; solute: 17.9 h) and mixed seed (particle 33.0 h; solute: 30.2 h) diets. Lack of selective retention of solutes and small particles in the bilby gastrointestinal tract probably restricts them to relatively low-fibre diets, such as those based on seeds rather than leaves and stems of plants. It was observed radiographically that the major sites of digesta retention were the caecum, proximal colon and distal colon, and thus the hindgut is probably the principal site of microbial fermentation. The mealworms were more digestible than the mixed seeds, but digestible energy intake (mealworm: 939 kJ · kg^−0.75 · d⁻¹; mixed seed: 629 kJ · kg^−0.75 · d⁻¹) was high enough for maintenance of body mass and positive nitrogen balance on both diets. Thus, although bilbies may be limited in their ability to utilize high-fibre diets by a lack of selective retention of solutes and small particles in their hindgut, their digestive strategy is flexible enough to accommodate at least some diets of both animal and plant origin. Such a strategy should benefit an animal inhabiting environments in which food resources are unpredictable in their relative abundance. Accepted: 26 May 2000     

Periodic fluid extrusion and models of digesta mixing in the intestine of a herbivore,the common brushtail possum (<Emphasis Type="Italic">Trichosurus vulpecula</Emphasis>)

The digesta in four gut compartments (proximal and distal halves of small intestine, caecum, and proximal colon) of a wild hindgut fermenting herbivore, the common brushtail possum (Trichosurus vulpecula), were investigated by rheometry and permeametry. Digesta from all compartments were highly viscous and exhibited shear-thinning. Apparent viscosity was positively related to dry matter content, and increased from proximal small intestine to colon. Dynamic rheological measurements showed that in small intestinal digesta the elastic modulus was greater than the viscous modulus and their ratios were characteristic of weak gels, indicating that digesta could sustain compression. The apparent viscosity of distal small intestinal digesta was markedly lower when measured by capillary viscometry than by rotatory viscometry, indicating that plug flow was likely to be facilitated by lubrication from a peripheral layer of less viscous fluid; i.e., there was an augmented plug flow. Permeametry showed that fluid was extruded from all digesta on compression at physiological pressures, that there was significant permeability of proximal and distal small intestinal digesta, but that digesta became progressively compacted during permeation, with a concomitant reduction in permeability as dry matter content increased. It is proposed that conditions within the small intestine differ from those of an ideal plug flow reactor as radial mixing and turbulence cannot occur. Instead, we suggest that segmentation and peristalsis aid radial mixing of the fluid phase by compressing the solid phase, with extrusion of fluid through the digesta plug. This extrusion may be followed by resorption of fluid back into the plug when the elasticity of the solid phase of digesta is Hookean, thus aiding the mixing of secreted enzymes with insoluble substrates within the plug.     

Harvesting, rumination, digestion, and passage of fruit and leaf diets by a small ruminant, the blue duiker

Because small ruminants (<15 kg) have a high ratio of metabolic rate to fermentation capacity, they are expected to select and require low-fiber, nutrient-dense concentrate diets. However, recent studies suggest that small ruminants may not be as limited in their digestive capacity as previously thought. In this study, we examined harvesting, rumination, digestion, and passage of three diets (domestic figs Ficus carica, fresh alfalfa Medicago sativa, and Pacific willow leaves Salix lasiandra) ranging from 10 to 50% neutral detergent fiber content (NDF) in captive blue duikers (Cephalophus monticola, 4 kg). Harvesting and rumination rates were obtained by observing and videotaping animals on each diet, and digestibility and intake were determined by conducting total collection digestion trials. We estimated mean retention time of liquid and particulate digesta by administering Co-EDTA and forages labelled with YbNO₃ in a pulse dose and monitoring fecal output over 4 days. Duikers harvested and ruminated the fig diet faster than the alfalfa and willow diets. Likewise, they achieved higher dry matter, energy, NDF, and protein digestibility when eating figs, yet achieved a higher daily digestible energy intake on the fresh willow and alfalfa than on the figs by eating proportionately more of these forages. Duikers maintained a positive nitrogen balance on all diets, including figs, which contained only 6.3% crude protein. Mean retention time of cell wall in the duikers’ digestive tract declined with increasing NDF and cellulose content of the diet. Digestibility coefficients and mean retention times of these small ruminants were virtually equivalent to those measured for ruminants two orders of magnitude larger, suggesting that they are well adapted for a mixed diet. Received: 10 August 1999 / Accepted: 16 November 1999     

An analysis of chewed food particle size and its relationship to molar structure in the primatesCheirogaleus medius andGalago senegalensis and the insectivoranTupaia glis

The chewed food particle size and shearing capacity of the lower molars of two primate species, the fat-tailed dwarf lemur,Cheirogaleus medius and the bushbabyGalago senegalensis, and an insectivoran, the tree shrew,Tupaia glis, were compared. Differences in the shearing design of the lower molars correlate strongly with the chewed food particle size in these species: the greater the shearing capacity, the smaller the chewed food particles. These three species are of comparable size but differ greatly in diet in the wild.C. medius primarily eats fruit and nectar, whileG. senegalensis andT. glis are largely insect-eaters. The lower molars ofG. senegalensis andT. glis show a much greater shearing capacity than do those ofC. medius. The average length of chewed food particles ofC. medius is significantly larger than that ofG. senegalensis, while that ofT. glis is intermediate between the two primates but is closer to that ofG. senegalensis. Our findings that insect-eating species grind their food more finely than do fruit- and resin-eating species can be correlated with digestibility of foods: finely chewing foods such as fruits which are low in relatively undigestible cell wall components would not greatly improve their digestibility, so a highly efficient food processing apparatus would be less important to the animal's survival. Insect-eaters much more finely chew their foods, implying that there is some constituent of insect bodies difficult to digest, and that grinding increases its digestibility. We suggest that this constituent is chitin.     

Efficiency of particle retention and clearance rate in the polychaete Sabellaria alveolata L

The development of Sabellaria alveolata, a gregarious reef-building polychaete species, is maximal in Mont-Saint-Michel Bay (France), where trophic capacity is now threatened by increasing shellfish farming. As no data are available concerning the ecophysiological response of this species, the purpose of the present study was to obtain clearance rate and retention efficiency values to provide a first order of magnitude for the trophic role of this species. Data were obtained using a flow-through system with novel troughs suitable for 225 cm2 reef blocks containing a mean number of 940 +/- 102 (S.E.) individuals. The experimental diet used consisted of a mixture of two live microalgae, Skeletonema costatum (3800 cell ml-1) and Isochrysis galbana (23,700 cell ml-1), chosen to cover a broad size range (2 to 16 microns equivalent spherical diameter, ESD), as determined by a particle counter. On the basis of a mean clearance rate of 0.7 lh-1 obtained with reef blocks, the mean rate for an individual was estimated at 7.5 x 10(-4) L h-1. Particles larger than 6 microns ESD were cleared with 100% efficiency, but S. alveolata was unable to retain particles smaller than 2 microns ESD. The results are compared with data obtained for other polychaete species, and clearance rate values are extrapolated to an entire reef.     

Effects of a dietary organic acid mixture and of dietary fibre levels on ileal and faecal nutrient apparent digestibility, bacterial nitrogen flow, microbial metabolite concentrations and rate of passage in the digestive tract of pigs

Six 34-kg barrows were fitted with a post-valve T-caecum cannula and assigned to six dietary treatments according to a 6 × 5 change-over design to study how a mixture of formic acid, sorbate, and benzoate (0 or 8.4 g/kg feed) influences apparent ileal and faecal digestibility coefficients, bacterial nitrogen (N) flow, microbial metabolite concentrations, and passage rate in pigs fed isoenergetic diets with medium, high, or very high fibre content (neutral-detergent fibre (NDF): 199, 224, and 248 g/kg dry matter, respectively). These barley and soya-bean meal based diets contained 0, 75, and 150 g/kg barley fibre (NDF: 577 g/kg) and 0, 8, and 16 g/kg rapeseed oil, respectively. The dietary organic acid mixture improved the apparent ileal digestibility of 14 of the 17 amino acids analysed (P < 0.05). Increasing levels of dietary fibre linearly decreased the apparent ileal digestibility of six of the 17 amino acids analysed (P < 0.05). Ileal flows of bacterial N and amino acids as assessed on the basis of purine flow were decreased by the dietary organic acid mixture (P < 0.05) but were not affected by dietary fibre level (P>0.05). As assessed on the basis of diaminopimelic acid flow, bacterial N flow was increased by both the dietary organic acid mixture and increased dietary fibre levels (P < 0.05). The dietary organic acid mixture reduced the concentration of lactic acid and increased that of acetic acid in ileal digesta (P < 0.05), while dietary fibre levels had a quadratic effect on concentrations of acetic, propionic, and butyric acid (P < 0.05). The mean retention time of Co (solute marker) and Yb (particle marker) in the large intestine decreased in a linear manner by increasing dietary fibre levels (P < 0.05) but was not affected by the dietary organic acid mixture (P>0.05). The results show that a dietary organic acid mixture has a positive effect on the apparent ileal digestibility of most amino acids irrespective of dietary fibre levels. This could be at least partly related to changes in bacterial N flow in the ileum. However, different bacterial markers showed opposite effects on bacterial N flow, which makes it questionable to use a constant bacterial marker / bacterial N ratio to estimate bacterial N flow. Increasing levels of dietary fibre had negative effects on the apparent ileal amino acid digestibilities and shortened the mean retention time of digesta in the large intestine.     

Food consumption and retention time in captive whooping cranes (Grus americana)

Food consumption, digesta retention time, and food preference were measured for captive whooping cranes fed pelleted diets. The basal commercial diet was compared to four mixtures containing 70% basal and 30% of one of four important winter foods for the whooping crane: blue crab (Callinectes sapidus), wolfberry fruit (Lycium carolinianum), live oak acorn (Quercus virginiana), or common Rangia clam (Rangia cuneata). Because captive birds would not eat whole foods, we were prevented from direct food preference tests. Food passed through the gut rapidly, with almost complete elimination within 7 hr. There was some indication that retention time was shorter for the low fiber and high ash and calcium clam diet. Cranes ate less wolfberry feed (g/day) than the other feeds, and all birds ate less wolfberry feed on the day it was first fed, compared to basal diet the previous day. Birds ate more low energy feed than high energy feed. Due to combined effects of low energy content, lower metabolizable energy coefficients, and reduced feed consumption, less energy was assimilated for study diets than basal diet. Apparent shorter retention times for some diets containing whooping crane foods may partly explain lower digestibilities and metabolizable energy of winter whooping crane foods compared to commercial crane diet. Zoo Biol 16:519–531, 1997. © 1997 Wiley-Liss, Inc.     

Fermentation of plant cell walls by ruminal bacteria,protozoa and fungi and their interaction with fibre particle size

Abstract

The objective of the experiment was to evaluate the contribution of various ruminal microbial groups to the fermentation of cell walls of corn stover with different particle sizes based on ruminal gas production in vitro. Physical, chemical, and antibiotical methods were used to differentiate groups of bacteria, protozoa and fungi in rumen fluid, offering following rumen microbial groups: whole rumen fluid (WRF), bacterial (B), protozoal (P), fungal (F), bacterial plus protozoal (B + P), bacterial plus fungal (B + F), protozoal plus fungal (P + F), and negative control (CON). Cell walls from corn stover were ground and ball milled to produce two different particle sizes. The results showed that digestion of the cell walls was undertaken by the interaction among ruminal bacteria, protozoa and fungi, and such co-actions seemed to fail alternation by one of three microbial groups or any combinations. However, B + P group showed a significant contribution to the degradation of milled cell walls, and B + F group revealed a great synergy effect on the ground cell walls degradation. Particle size of cell walls also had a considerable influence on their fermentation extent instead of the fermentative patterns by various rumen microbial groups.     

Rhythmic pattern of growth and nutrient retention in response to feeding time in the rainbow trout

The effect of six different feeding times was tested on feed intake, growth performance, proximate body composition and nutrient retention in the rainbow trout Oncorhynchus mykiss . Using a non‐linear regression model, a significant rhythmic pattern over a 24 h period was observed for feed gain ratio and nutrient retention responses to feeding time. Specific growth rate and protein growth rate responses were also rhythmic but the trends were not significant. There was no clear effect of feeding time on feed intake and proximate body composition. The study suggested that feed intake, at least under the experimental conditions encountered, was synchronized to feeding time while some physiological rhythms involved in nutrient metabolism were probably synchronized to photoperiod.     

Transport and particle size distribution of suspended and benthic organic matter in three headwater streams

The breakdown and decomposition of two species of deciduous leaf litter, Fagus sylvatica L. and Salix viminalis L. and two species of aquatic macrophyte Isoetes lacustris L. and Potamogeton perfoliatus L. were examined in an oligotrophic lake. In all cases plant litter in coarse mesh litter bags lost significantly more material than the fine mesh after 1 years submergence in the lake. This however was considered to be the result of physical environmental factors and microbial activity rather than animal processing. The litter was ranked in order of fastest to slowest rates of decay as follows — Isoetes, Potamogeton, Salix and Fagus. Decomposition processes proceeded at a relatively slow rate as a result of low temperatures and low phosphate and mineral ion concentration. The results suggested that there was an accumulation of organic material in the lake.