Comparison of fibre digestion and digesta retention time between rabbits, guinea-pigs, rats and hamsters

An analysis of the cecum microbiome of three breeds of the guinea pig: Andina, Inti, and Peru

This study investigated the effect of host genetics on the structure and composition of the cecum microbiota of three breeds of guinea pigs: Andina, Inti, and Peru. Fifteen guinea pigs were distributed into three groups according to their breed: Andina (5), Inti (5), and Peru (5). We discovered that four main phyla were shared between the three breeds: Bacteroidota, Firmicutes, Spirochaetota, and Synergistota. Although there were no significant differences in the alpha and beta diversity analysis, we found that the Linear discriminant analysis effect size and the heat tree analysis showed significant differences between the abundance of several taxa present in the cecum microbiome of the three breeds. These results suggest that host genetics could be a factor in the structure and composition of the guinea pig cecum microbiome. In addition, we found unique genera for each breed that have fermentation capacity and, therefore can be analyzed in further studies to determine if there is a functional relationship between them and the breed and its industrial profile.

Digestion of bamboo compared to grass and lucerne in a small hindgut fermenting herbivore, the guinea pig (Cavia porcellus)

Bamboo is an enigmatic forage, representing a niche food for pandas and bamboo lemurs. Bamboo might not represent a suitable forage for herbivores relying on fermentative digestion, potentially due to its low fermentability. To test this hypothesis, guinea pigs (n = 36) were used as model species and fed ad libitum with one of three forages (bamboo, lucerne, or timothy grass) in a fresh or dried state, with six individuals per group, for 3 weeks. The nutrient composition and in vitro fermentation profile of bamboo displayed low fermentation potential, i.e. high lignin and silica levels together with a gas production (Hohenheim gas test) at 12 h of only 36% of that of lucerne and grass. Although silica levels were more abundant in the leftovers of (almost) all groups, guinea pigs did not select against lignin on bamboo. Dry matter (DM) intake was highest and DM digestibility lowest on the bamboo forage. Total short-chain fatty acid levels in caecal content were highest for lucerne and lowest for grass and bamboo. Bamboo-fed guinea pigs had a lower body weight gain than the grass and lucerne group. The forage hydration state did not substantially affect digestion, but dry forage led to a numerically higher total wet gut fill. Although guinea pigs increased DM intake on the bamboo diet, the negative effects on fermentation of lignin and silica in bamboo seemed overriding. For herbivores that did not evolutionary adapt, bamboo as an exclusive food resource can be considered as inadequate.

Good to Know: Baseline Data on Feed Intake, Fecal Pellet Output and Intestinal Transit Time in Guinea Pig as a Frequently Used Model in Gastrointestinal Research

Simple Summary

Guinea pigs are frequently used in gastrointestinal research, but knowledge on basic parameters connected with gastrointestinal physiological functions, including feed intake, fecal pellet output (FPO) and intestinal transit time, is incomplete. Recording such parameters in single- and pair-housed guinea pigs over 24 h revealed that they exhibit a diurnal feeding behavior, with peaks during the beginning and end of the light period, and FPO mirroring periods, with a defecation break during the night. In addition, we assessed transit time with a non-absorbable marker, counting approximately 5 h. Our findings can help to build a baseline data basis, important in the field of functional gastrointestinal animal physiology.

Abstract

Guinea pigs are a traditional and frequently used species in gastrointestinal research. Comprehensive knowledge of basic parameters connected with their intestinal function, such as feed intake, fecal pellet output and gastrointestinal transit time, is important for evaluating results from basic gastrointestinal research that may be applied to practical problems in human and veterinary medicine, for example, when establishing diagnostic tools. Our study revealed that over a 24-h period, single-housed guinea pigs showed a continual but day-accentuated feeding activity, consuming 57% of the total feed during the light period, with pronounced peaks of feed intake during the beginning and end of the light period. This was mirrored by fecal pellet output during the light period and almost no defecation during the dark period, while potential coprophagy not measured in this study needs to be considered. A highly comparable feeding activity was recorded in pair-housed guinea pigs, with 60% of overall feed intake within the light period, indicating that such differences in housing conditions did not influence guinea pigs’ feeding behavior. Intestinal transit time was successfully recorded by oral administration of carmine red and counted 5 h on average. Hence, this study provides important information on the basic functional parameters of guinea pigs’ gastrointestinal tract physiology.

Comparative Analysis of Fecal Microbiota in Grasscutter (Thryonomys swinderianus) and Other Herbivorous Livestock in Ghana

The grasscutter (also known as the greater cane rat; Thryonomys swinderianus) is a large rodent native to West Africa that is currently under domestication process for meat production. However, little is known about the physiology of this species. In the present study, aiming to provide information about gut microbiota of the grasscutter and better understand its physiology, we investigated the intestinal microbiota of grasscutters and compared it with that of other livestock (cattle, goat, rabbit, and sheep) using 16S rRNA metagenomics analysis. Similar to the other herbivorous animals, bacteria classified as Bacteroidales, Clostridiales, Ruminococcaceae, and Lachnospiraceae were abundant in the microbiome of grasscutters. However, Prevotella and Treponema bacteria, which have fiber fermentation ability, were especially abundant in grasscutters, where the relative abundance of these genera was higher than that in the other animals. The presence of these genera might confer grasscutters the ability to easily breakdown dietary fibers. Diets for grasscutters should be made from ingredients not consumed by humans to avoid competition for resources and the ability to digest fibers may allow the use of fiber-rich feed materials not used by humans. Our findings serve as reference and support future studies on changes in the gut microbiota of the grasscutter as domestication progresses in order to establish appropriate feeding methods and captivity conditions.

Diet changes alter paternally inherited epigenetic pattern in male Wild guinea pigs

Epigenetic modifications, of which DNA methylation is the most stable, are a mechanism conveying environmental information to subsequent generations via parental germ lines. The paternal contribution to adaptive processes in the offspring might be crucial, but has been widely neglected in comparison to the maternal one. To address the paternal impact on the offspring's adaptability to changes in diet composition, we investigated if low protein diet (LPD) in F0 males caused epigenetic alterations in their subsequently sired sons. We therefore fed F0 male Wild guinea pigs with a diet lowered in protein content (LPD) and investigated DNA methylation in sons sired before and after their father's LPD treatment in both, liver and testis tissues. Our results point to a 'heritable epigenetic response' of the sons to the fathers' dietary change. Because we detected methylation changes also in the testis tissue, they are likely to be transmitted to the F2 generation. Gene-network analyses of differentially methylated genes in liver identified main metabolic pathways indicating a metabolic reprogramming ('metabolic shift'). Epigenetic mechanisms, allowing an immediate and inherited adaptation may thus be important for the survival of species in the context of a persistently changing environment, such as climate change.

Pregastric and caecal fermentation pattern in Syrian hamsters

Few studies have compared the pregastric and caecal digestion of hamsters. Mature Syrian hamsters (

Transfer of blood urea nitrogen to cecal microbial nitrogen is increased by fructo-oligosaccharide feeding in guinea pigs

The present study was conducted to determine the mechanism by which nitrogen (N) availability is improved by fructo-oligosaccharide (FOS) in guinea pigs. Adult male guinea pigs were fed a commercial pellet diet (50 g/day) with either 5% glucose or 5% FOS for 7 days in individual metabolism cages. After 7 days of feeding the diet, (15) N-urea was administered intravenously 1 h before slaughter under anesthesia. The amount and concentration of total, protein, bacterial, ammonia and urea N and the (15) N atom % excess were measured in blood, liver, gut contents and urine. The (15) N atom % excess of total and protein N, and the amount of total, protein and bacteria N and (15) N in the cecum were significantly increased by the consumption of FOS. Furthermore, the concentration and amount of short-chain fatty acids were significantly increased by the consumption of FOS. In contrast, the amount of urinary (15) N was significantly decreased by the consumption of FOS. These results suggest that consumption of FOS increases transfer of blood urea N into the large intestine for bacterial N synthesis, which is subsequently re-absorbed by cecotrophy, and contributes to the increase of N utilization in guinea pigs.

Dietary fructooligosaccharides and wheat bran elicit specific and dose-dependent gene expression profiles in the proximal colon epithelia of healthy Fischer 344 rats

Proximal colon epithelial gene responses to diets containing increasing levels of dietary fermentable material (FM) from 2 different sources were measured to determine whether gene expression patterns were independent of the source of FM. Male Fischer 344 rats (10/group) were fed for 6 wk a control diet containing 10% (g/g) cellulose (0% FM); or a 2, 5, or 10% wheat bran (WB) diet (1, 2, 5% FM); or a 2, 5, or 8% fructooligosaccharides (FOS) diet (2, 5, 8% FM). WB and FOS were substituted for cellulose to give a final 10% nondigestible material content including FM. Gene responses were relative to expression in rats fed the control diet. The gene response patterns associated with feeding ∼2% FM (5% WB and 2% FOS) were similar (∼10 gene changes ≥ 1.6-fold; P ≤ 0.01) and involved genes associated with transport (Scnn1g, Mt1a), transcription (Zbtb16, Egr1), immunity (Fkbp5), a gut hormone (Retn1β), and lipid metabolism (Scd2, Insig1). These changes were also similar to those associated with 5% FM but only in rats fed the 10% WB diet. In contrast, the 5% FOS diet (~5% FM) was associated with 68 gene expression changes ≥ 1.6-fold (P ≤ 0.01). The diet with the highest level of fermentation (8% FOS, ~8% FM) was associated with 132 changes ≥ 1.6-fold (P ≤ 0.01), including genes associated with transport, cellular proliferation, oncogene and tumor metastasis, the cell cycle, apoptosis, signal transduction, transcript regulation, immunity, gut hormones, and lipid metabolic processes. These results show that both the amount and source of FM determine proximal colon epithelial gene response patterns in rats.

A formulation comparison between micro- and nanosuspensions: the importance of particle size for absorption of a model compound, following repeated oral administration to rats during early development

AIM

The aim of this study was to maximize the exposure of a model compound (MC) for forthcoming high-dose toxicological studies with the physical form of the original compound unaffected.

METHOD

The two evaluated formulation approaches for the present poorly water-soluble compound were micro- and nanosuspensions.

RESULTS

The particle size was about 280 nm for the nanosuspensions and about 4 μm for the microsuspensions. The crystallinity and the crystalline form of the ground samples were conserved. The physical and the chemical stabilities of the two kinds of suspensions were unaffected during the investigated time period. The in vivo results of the study showed that the pharmacokinetic parameters investigated were comparable at the low-dose level (6 μmol/kg) for both formulations after single administration. However, at the two higher doses (60 and 300 μmol/kg), a significant difference in exposure was observed between the two suspensions with an improved exposure for smaller particles. After Day 7 of repeated administration, a significant difference in exposure was observed at all dose levels. The overall exposures were higher on Day 7, compared to the exposures on Day 1 (most significant for nanoparticles), due to an accumulation of compound in the body.

CONCLUSIONS

The nanoparticles have a larger surface, resulting in faster in vivo dissolution rate, faster absorption, and increased bioavailability, compared to microparticles. The differences in systemic exposure of model compound, following oral administration of nano- or microparticles of the drug substance, are probably caused by differences in the in vivo dissolution rate and possibly further enhanced by saturation of the systemic elimination.

Effect of D-mannitol on feed digestion and cecotrophic system in rabbits

This study aimed to evaluate the effect of sugar alcohol as an energy source for cecal microbes on digestibility, cecotrophy (i.e. reingestion of microbial products of cecum, cecotrophs) and performance in rabbits. Thus, we fed rabbits an experimental diet that included 5% of D-mannitol, and collected hard feces and cecotrophs to be analyzed for crude protein (CP), acid detergent fiber (ADF), ether extract (EE), crude ash (CA) and dry matter (DM). Cecotrophic behavior of the rabbits was also observed. Feeding D-mannitol increased (P < 0.01) digestibility of ADF, resulting in a decrease (P < 0.05) in the concentration in hard feces. The increase (P < 0.05) in CP concentration was attributed to lower (P < 0.05) digestibility. D-mannitol had a similar modulatory effect on CP and ADF concentrations in hard feces and cecotrophs. Accordingly, estimations of the proportion of nutrients recycled by cecotrophy to dietary intake (PR), obtained by the two calculation methods, showed an increase (P < 0.01) in PR of CP and a decrease (P < 0.05) in that of ADF. Daily weight gain and feed efficiency increased (P < 0.05) for D-mannitol-fed rabbits, while daily feed intake decreased (P < 0.05). These results suggest the possibility of using D-mannitol as a stimulator of cecal microbial growth and cellulolytic activity, and therefore, improved rabbits performance.

Protein hydrolysates are avoided by herbivores but not by omnivores in two-choice preference tests

BACKGROUND

The negative sensory properties of casein hydrolysates (HC) often limit their usage in products intended for human consumption, despite HC being nutritious and having many functional benefits. Recent, but taxonomically limited, evidence suggests that other animals also avoid consuming HC when alternatives exist.

METHODOLOGY/PRINCIPAL FINDINGS

We evaluated ingestive responses of five herbivorous species (guinea pig, mountain beaver, gopher, vole, and rabbit) and five omnivorous species (rat, coyote, house mouse, white-footed mouse, and deer mouse; N = 16-18/species) using solid foods containing 20% HC in a series of two-choice preference tests that used a non-protein, cellulose-based alternative. Individuals were also tested with collagen hydrolysate (gelatin; GE) to determine whether it would induce similar ingestive responses to those induced by HC. Despite HC and GE having very different nutritional and sensory qualities, both hydrolysates produced similar preference score patterns. We found that the herbivores generally avoided the hydrolysates while the omnivores consumed them at similar levels to the cellulose diet or, more rarely, preferred them (HC by the white-footed mouse; GE by the rat). Follow-up preference tests pairing HC and the nutritionally equivalent intact casein (C) were performed on the three mouse species and the guinea pigs. For the mice, mean HC preference scores were lower in the HC v C compared to the HC v Cel tests, indicating that HC's sensory qualities negatively affected its consumption. However, responses were species-specific. For the guinea pigs, repeated exposure to HC or C (4.7-h sessions; N = 10) were found to increase subsequent HC preference scores in an HC v C preference test, which was interpreted in the light of conservative foraging strategies thought to typify herbivores.

CONCLUSIONS/SIGNIFICANCE

This is the first empirical study of dietary niche-related taxonomic differences in ingestive responses to protein hydrolysates using multiple species under comparable conditions. Our results provide a basis for future work in sensory, physiological, and behavioral mechanisms of hydrolysate avoidance and on the potential use of hydrolysates for pest management.

A case of non-scaling in mammalian physiology? Body size, digestive capacity, food intake, and ingesta passage in mammalian herbivores

As gut capacity is assumed to scale linearly to body mass (BM), and dry matter intake (DMI) to metabolic body weight (BM(0.75)), it has been proposed that ingesta mean retention time (MRT) should scale to BM(0.25) in herbivorous mammals. We test these assumptions with the most comprehensive literature data collations (n=74 species for gut capacity, n=93 species for DMI and MRT) to date. For MRT, only data from studies was used during which DMI was also recorded. Gut capacity scaled to BM(1.06). In spite of large differences in feeding regimes, absolute DMI (kg/d) scaled to BM(0.76) across all species tested. Regardless of this allometry inherent in the dataset, there was only a very low allometric scaling of MRT with BM(0.14) across all species. If species were divided according to the morphophysiological design of their digestive tract, there was non-significant scaling of MRT with BM(0.04) in colon fermenters, BM(0.08) in non-ruminant foregut fermenters, BM(0.06) in browsing and BM(0.04) in grazing ruminants. In contrast, MRT significantly scaled to BM(0.24) (CI 0.16-0.33) in the caecum fermenters. The results suggest that below a certain body size, long MRTs cannot be achieved even though coprophagy is performed; this supports the assumption of a potential body size limitation for herbivory on the lower end of the body size range. However, above a 500 g-threshold, there is no indication of a substantial general increase of MRT with BM. We therefore consider ingesta retention in mammalian herbivores an example of a biological, time-dependent variable that can, on an interspecific level, be dissociated from a supposed obligatory allometric scaling by the morphophysiological design of the digestive tract. We propose that very large body size does not automatically imply a digestive advantage, because long MRTs do not seem to be a characteristic of very large species only. A comparison of the relative DMI (g/kg(0.75)) with MRT indicates that, on an interspecific level, higher intakes are correlated to shorter MRTs in caecum, colon and non-ruminant foregut fermenters; in contrast, no significant correlation between relative DMI and MRT is evident in ruminants.

Demonstrating coprophagy with passage markers? The example of the plains viscacha (Lagostomus maximus)

Coprophagy, or the ingestion of a certain fraction of the faeces, is a well-known strategy of small herbivores. However, the question of whether a particular species actually uses this cryptic strategy or not is not easily answered experimentally. In this study we introduce the use of ingesta passage markers as a tool to verify coprophagy in species where individual observation might be difficult. In two captive adult plains viscachas (Lagostomus maximus), we demonstrate recurrent excretion peaks for both a fluid (cobald-EDTA) and a particle (chromium-mordanted fibre) marker, the most parsimonious explanation for which is faeces re-ingestion. In addition, a literature review of graphical presentations of passage marker excretion revealed such recurrent marker peaks in a large number of studies; however, these observations were rarely explicitly contributed to a coprophagic digestion strategy. The widespread use of semi-logarithmic plots or cumulative marker excretion curves in displaying passage studies makes recurrent marker excretion peaks less evident. We conclude that passage markers offer a comparatively easy way of assessing the incidence of coprophagy. Due to the reported absence of coprophagy in rabbits, a species well-known for using this strategy, on high-protein, low-fibre diets, it is recommended that investigations of the occurrence of coprophagy should be made with animals fed challenging, high-fibre diets.

Effects of diet quality on phenotypic flexibility of organ size and digestive function in Mongolian gerbils (Meriones unguiculatus)

In the context of evolution and ecology, there is a trade-off between the benefits of processing food through a digestive system with specific phenotypic attributes and the cost of maintaining and carrying the digestive system. In this study, we tested the hypothesis that digestive modulations at several levels can match each other to meet the energy and nutrient demands of Mongolian gerbils, a small granivorous rodent species, by acclimating them to a high-quality diet diluted with alfalfa powder. Mongolian gerbils on the diluted diet maintained metabolizable energy intake by an integrated processing response (IPR), which included increases in dry matter intake, gut capacity and rate of digesta passage after 2-weeks of acclimation. Down-regulation of hydrolytic enzyme activity in the intestinal brush-border membrane supported the adaptive modulation hypothesis. The absence of up-modulation of summed enzyme hydrolytic capacity on the diluted diet indicated that greater mass of small intestine on a high-fibre diet is not a direct indicator of digestive or absorptive capacity. Changes in mass of vital organs and carcass suggested that the amount of energy allocated to various organs and hence physiological functions was regulated in response to diet shift.

Transport of bacteria across and along the large intestinal lumen of guinea pigs

Flow cytometry was used to observe the transport of fluorescently labelled viable bacteria in the large intestinal lumen of guinea pigs after the injection of the bacteria into the proximal colon. Bacteria were transported along the radial and longitudinal axes of the intestine and were separated from dietary residue, accumulated, and then transported back to the caecum. These observations, together with the heterogeneous distribution of bacterial species and chemical composition across and along the large intestine, suggest that there are several different microenvironments within the intestinal lumen between which bacteria and/or dietary residues move. The existence of different microenvironments within the intestinal lumen is consistent with poor mixing of the digesta within the large intestine of pigs and chickens.

Symbiotic fermentation, digesta passage, and gastrointestinal morphology in bullfrog tadpoles (Rana catesbeiana)

Relative to other herbivorous vertebrates, the nutritional ecology and digestive physiology of anuran larvae remain poorly understood. Our objective was to compare gut structure and inhabitants, digesta passage, and microbial fermentation in bullfrog tadpoles (Rana catesbeiana) to those in other herbivores. Bullfrog tadpole gastrointestinal tracts were long and voluminous, with an enlarged colon that harbored a diverse symbiotic community. The transit time for particulate markers passing through bullfrog tadpoles was 6 h, the median retention time was 8-10 h, and gut clearance was 10-14 h postingestion. Relatively high levels of short-chain fatty acids in the hindgut of tadpoles indicated active microbial fermentation in this gut region. This report represents the first account of gastrointestinal fermentation in the class Amphibia. On the basis of in vitro fermentation assays, we estimated that microbial fermentation in the hindgut provides 20% of the total daily energy requirement of bullfrog tadpoles. These tadpoles also exhibited coprophagy, a practice that provides important nutritive gains in other herbivores. The physiological and behavioral characteristics of these tadpoles are remarkably similar to those of other small-bodied, hindgut-fermenting vertebrates, suggesting convergent digestive strategies among a broad range of herbivorous taxa.

Five month persistence of Helicobacter pylori infection in guinea pigs

Seven Dunkin-Hartley guinea pigs were infected with the Sydney strain of H. pylori (SS1). Gastric histopathology was evaluated and serum antibody response to H. pylori cell-surface proteins was analysed by enzyme immunoassay (EIA) and immunoblot. Tissue and faecal samples from five control animals were analysed for the presence of naturally occurring Helicobacter spp. infection by culture and Helicobacter genus-specific PCR. The H. pylori infection persisted for 5 months, in most animals accompanied by a histologically severe antral gastritis, exhibiting focal degeneration and necrosis of gastric crypt epithelium. Increased numbers of mitotic figures were observed in the gastric epithelium, indicating a regenerative process. Infected animals displayed specific antibodies towards H. pylori cell-surface proteins in immunoblot, whereas EIA was of dubious value creating false-positive results. Serum complement C3 and cholesterol levels appeared to be elevated in infected animals. Helicobacter spp. infection was not detected in the control animals. The persistent infection, accompanied by severe gastritis and a prominent serum antibody response, and the apparent absence of a natural Helicobacter spp. infection makes the guinea pig model useful in H. pylori research.

Effect of low protein and low energy diet on physiological status and digestibility of F344 rats

A long-term raising study was carried out on male F344/DuCrj rats with three low protein (Crude Protein (CP); 14.5, 11.5, 8.5%) and low energy (Digestible Energy (DE); 2.0 kcal/g) diets from 4 to 104 weeks of age. In rats fed the 8.5% CP diet, body weight and digestible crude protein (DCP) consumption at 10 weeks of age were lower (P < 0.05) but the body weight at 50 weeks of age was higher (P < 0.05) than in the other groups. In rats fed the 8.5% CP diet the crude fat digestibility was higher (P < 0.05), and the CP/nitrogen-corrected metabolizable energy (MEn) ratio was low. On the other hand, the mean survival time at 80 weeks of age was shorter in rats fed the 8.5% CP diet (P < 0.05).

Dietary fructooligosaccharides modify intestinal bioavailability of a single dose of genistein and daidzein and affect their urinary excretion and kinetics in blood of rats

The influence of dietary fructooligosaccharides (FOS) on bioavailability of genistein and daidzein in rats was estimated by measuring their concentrations in plasma collected from three different veins and in urine after a single intragastric administration of isoflavone conjugates. Sprague-Dawley male rats (6 wk old, n = 22) were fed a purified control (AIN-93G) diet or a FOS diet (AIN-93G + 5% FOS) for 7 d. A single dose of soy isoflavone conjugates, i.e., 8.5 mg as genistein and 33 mg as daidzein/kg body, was administered via a stomach tube at d 5. Blood samples were collected after administration via catheters in the portal and central veins and by puncture of the tail vein. The isoflavones in plasma and urine were analyzed by time-resolved fluoroimmunoassay. The genistein concentration in the portal blood increased rapidly, reaching a peak of 3.5 micromol/L in both groups at 1 h after administration. The concentrations in the central and tail venous blood were approximately half of those in the portal blood. In the FOS-fed group, both genistein and daidzein remained detectable at 24 and 48 h in the tail venous plasma. The urinary excretion of both isoflavones in the 24- to 48-h period after administration was significantly higher in the FOS-fed group than in the control group. The difference between the portal and central veins indicated hepatic uptake, probably leading to conjugation of aglycones and excretion into bile. FOS modified the absorption and enterohepatic recirculation of isoflavones.

Digestibility, nitrogen excretion, and mean retention time by North American porcupines (Erethizon dorsatum) consuming natural forages

North American porcupines (Erethizon dorsatum) subsist predominantly on low-protein, high-fiber, high-tannin diets. Therefore, we measured the porcupine's ability to digest dry matter, fiber, and protein by conducting digestion trials on eight natural forages and one pelleted ration varying in concentration of fiber, nitrogen, and tannins. On these diets, dry matter intake ranged from 5 to 234 g/kg(0.75)/d and dry matter digestibility ranged from 62% to 96%. Porcupines digested highly lignified fiber better than many large hindgut fermenters and ruminants. The porcupine's ability to digest fiber may be explained, in part, by their lengthy mean retention time of particles (38.43+/-0.56 h). True nitrogen digestibility was 92% for nontannin forages and pellets. Endogenous urinary nitrogen was 205 mg N/kg(0.75)/d, and metabolic fecal nitrogen was 2.8 g N/kg dry matter intake. Porcupines achieved nitrogen balance at relatively low levels of nitrogen intake (346 mg N/kg(0.75)/d). Tannins reduced the porcupines' ability to digest protein. However, the reduction in protein digestion was not predictable from the amount of bovine serum albumin precipitated. Like many herbivores, porcupines may ameliorate the effects of certain tannins in natural forages on protein digestibility through physiological and behavioral adaptations.

The influence of fibre in the diet on growth rates and the digestibility of nutrients in the greater cane rat (Thryonomys swinderianus)

The greater cane rat Thryonomys swinderianus is a coprophagous rodent in which fermentation occurs in the large caecum. The extent to which a 45% increase in the fibre component of the diet influenced growth rates of cane rats and the digestibility of nutrients and energy was investigated in two feeding trials. Higher fibre levels in the diet reduced the digestibility of dry matter, protein and fat, while animals digested fibre components (neutral-detergent fibre, acid detergent fibre, hemicellulose and cellulose) with a comparable efficiency to those maintained on a low fibre diet. In one of the trials animals fed the high fibre diet exhibited significantly lower growth rates than animals fed the low fibre diet. Digestibility coefficients of the cane rats for neutral-detergent fibre and protein seem to be intermediate to high when compared to reported values for the porcupine, guinea-pig, degu and rabbit. It is suggested that the ability of cane rats to utilise large quantities of fibre enable them to survive periods when only dry grass is available.

Contributions of microbes in vertebrate gastrointestinal tract to production and conservation of nutrients

The vertebrate gastrointestinal tract is populated by bacteria and, in some species, protozoa and fungi that can convert dietary and endogenous substrates into absorbable nutrients. Because of a neutral pH and longer digesta retention time, the largest bacterial populations are found in the hindgut or large intestine of mammals, birds, reptiles, and adult amphibians and in the foregut of a few mammals and at least one species of bird. Bacteria ferment carbohydrates into short-chain fatty acids (SCFA), convert dietary and endogenous nitrogenous compounds into ammonia and microbial protein, and synthesize B vitamins. Absorption of SCFA provides energy for the gut epithelial cells and plays an important role in the absorption of Na and water. Ammonia absorption aids in the conservation of nitrogen and water. A larger gut capacity and longer digesta retention time provide herbivores with additional SCFA for maintenance energy and foregut-fermenting and copoprophagic hindgut-fermenting species with access to microbially synthesized protein and B vitamins. Protozoa and fungi also contribute nutrients to the host. This review discusses the contributions of gut microorganisms common to all vertebrates, the numerous digestive strategies that allow herbivores to maximize these contributions, and the effects of low-fiber diets and discontinuous feeding schedules on these microbial digestive processes.

Fiber digestion and weight gain in guinea pigs fed diets containing different fiber sources

The effects of different fiber sources on feed intake, weight gain and digestibility of fiber were examined in guinea-pigs fed pelleted diets containing alfalfa meal, oaten hay, beet pulp and commercial hay cubes mixed with a basal diet at ratios of 3:1 (75% in the diet), 1:1 (50%) and 1:3 (25%). The basal diet contained 50.0% corn, 4.1% wheat, 22.1% wheat flour and 17.7% corn gluten meal. Food intake increased as the amount of fiber source was increased, but not in the case of beet pulp. The most digestible fiber (ADF and NDF) was that of beet pulp. Apparent digestibility of dry matter decreased with increasing ratios of fiber source to the basal diet for all fiber sources, but fiber and crude protein digestibilities varied and depended not only on the ratio of fiber to the basal diet but also on the source of the fiber.

Application of agar-fill method to estimate compartment capacity of gastrointestinal tract in Syrian hamsters (Mesocricetus auretus)

In the present study we have developed the agar-fill method for the measurement of gastrointestinal-tract capacity (GTC) to replace the in vitro water-fill method. This would estimate GTC without using complex equipment and techniques, and can be applied to the measurement of GTC for small laboratory animals. We attempted to confirm the efficiency of the agar-fill method by investigating the relationship between dietary neutral-detergent fibre (NDF) content and GTC. The digestion trials were carried out using the Syrian hamster (Mesocricetus auretus). The trials were conducted using both sexes, two age-groups and three levels of dietary NDF with a cross-classified design. The size of each gastrointestinal organ was determined as tissue weight (TW) and GTC. The DM intake, digestible DM intake, DM digestibility, NDF digestibility, acid-detergent fibre (ADF) digestibility and digesta transit time were also measured. GTC increased with increasing NDF content of the diets. TW responded similarly to increasing NDF content, but the response was smaller than that of GTC. DM digestibility decreased with increasing NDF content of the diet. The digestible DM intake did not decrease with increasing NDF because DM intake increased with NDF content. Digesta transit time was not shorter of the high-NDF diet group but DM intake increased with increasing NDF content. NDF digestibility did not differ significantly between low- and medium-NDF diets. ADF digestibility was low in the low-NDF-diet group. The digestion characteristics were highly correlated with TW and GTC, except for TW of small intestine. These correlations were higher with GTC than with TW. The results of the present study confirm previous findings suggesting that the agar-fill method is a useful means of estimating GTC for small laboratory animals.

Food intake, nutrient utilization and water turnover in the lesser mouse-deer (Tragulus javanicus) given lundai (Sapium baccatum)

Voluntary food intake, digestibility and water turnover were determined in adult Malaysian lesser mouse-deer (Tragulus javanicus) given unlimited access to lundai foliage (Sapium baccatum). Daily dry matter (DM) intake was 42.4 g/kg metabolic live mass (M0.73) or 3.7% M. Digestible energy intake was 853 kJ/day (571 kJ metabolisable energy per M0.73), calculated to be used with 79% efficiency. Apparent digestibility (%) of organic matter was 83.8, crude fibre 63.7, acid detergent fibre 60.5, neutral detergent fibre 72.1 and crude protein 65.0. Urinary excretion of the purine derivative, allantoin, was 0.05 mg/g digestible DM intake suggesting rumen microbial yield efficiency may be lower than in other ruminant species. Total water intake was 182 ml/M0.82. The body-water content of the fed mouse-deer, from tritiated water dilution, was 77% M, consistent with a very lean carcass. Turnover of body water was 17% per day. The mouse-deer produced relatively dry, well-defined faecal pellets.

Distribution of activity of hydrolytic enzymes in the digestive tract of rabbits

Activities of twelve hydrolytic enzymes in the digestive tract of young rabbits before weaning (4 weeks old) and adult rabbits (3 months old) were measured. The principal digestive enzymes in both groups of rabbits appeared to be amylase (EC 3.2.1.1), maltase (EC 3.2.1.20), pectinase (EC 3.2.1.15) and proteinases. The stomach of young rabbits contained most of the lipolytic activity and 45.7% of the total proteolytic activity of the digestive tract. The highest specific activities (per g digesta) of amylase, maltase and proteinase in young rabbits were found in the small intestine. Total activities (per segment) of amylase and maltase in the small intestine and the caecum were similar. Activities of cellulase (EC 3.2.1.4), inulinase (EC 3.2.1.7) and beta-glucosidase (EC 3.2.1.21) were low and activity of pectinase was fairly high in all segments of the digestive tract. The highest activity of urease (EC 3.5.1.5) was found in the caecum. Enzymic profiles of the colonic chymus resembled those of the caecum. Total hydrolytic activity was lower in the colon than in the caecum. Specific activities of amylase and invertase (EC 3.2.1.26) were lower and those of inulinase and lactase (EC 3.2.1.23) higher in 4-week-old rabbits than in 3-month-old rabbits. Gastric proteinase represented almost half of the total proteolytic activity of the digestive tract, whereas lipolytic activity of gastric contents was not found in measurable quantities in adult rabbits. The caecal contents of adult rabbits contained most of the total activity of lipase (EC 3.1.1.3), cellulase, xylanase (EC 3.2.1.32), pectinase, lactase, invertase, beta-glucosidase and urease present in the digestive tract.(ABSTRACT TRUNCATED AT 250 WORDS)