Colonic Separation Mechanism in Lagomorph and Rodent Species - a Comparison

Teeth and the gastrointestinal tract in mammals: when 1 + 1 = 3

Both teeth and the digestive tract show adaptations that are commonly interpreted in the context of trophic guilds-faunivory, herbivory and omnivory. Teeth prepare food for the digestive tract, and dental evolution focuses on increasing durability and functionality; in particular, size reduction of plant particles is an important preparation for microbial fermentative digestion. In narratives of digestive adaptations, microbes are typically considered as service providers, facilitating digestion. That the majority of 'herbivorous' (and possibly 'omnivorous') mammals display adaptations to maximize microbes' use as prey-by harvesting the microbes multiplying in their guts-is less emphasized and not reflected in trophic labels. Harvesting of microbes occurs either via coprophagy after separation from indigestible material by a separation mechanism in the hindgut, or from a forestomach by a 'washing mechanism' that selectively removes fines, including microbes, to the lower digestive tract. The evolution of this washing mechanism as part of the microbe farming niche opened the opportunity for the evolution of another mechanism that links teeth and guts in an innovative way-the sorting and cleaning of not-yet-sufficiently-size-reduced food that is then re-submitted to repeated mastication (rumination), leading to unprecedented chewing and digestive efficiency. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.

Morphology of the digestive system of the lesser bamboo rat (Cannomys badius)

The lesser bamboo rat is a fossorial rodent within the monotypic genus Cannomys, family Spalacidae and is found in Indochina. The present work provides the first detailed description of the morphology of its digestive system, as examined by gross dissection and histological examination. The oesophagus was lined by a heavily keratinized epithelium and contained mostly striated muscles in the muscularis externa. The stomach was of the unilocular-hemiglandular type with a cornified squamous area at the fundus separated from the glandular area by the limiting ridge. The length ratio of the small intestine to the entire intestine was relatively low compared to that in other rodents. The caecum contained five to seven haustra and numerous lymphoid tissues, but no distinct appendix. Within the long colon, two non-papillated longitudinal folds forming a colonic groove, V-shaped mucosal folds like fishbones and abundant goblet cells were apparent. A five-lobed liver with a gallbladder and a diffuse pancreas were evident. These findings may indicate that the lesser bamboo rat is a caecal fermenter capable of feeding on highly abrasive plant material. Fermentation may take place via a mucus-trap colonic separation mechanism without coprophagy. The digestive system of the lesser bamboo rat is somewhat different from that of spalacid relatives.

Quantitative analysis of the distribution of the myenteric plexus in the rabbit large intestine

Rabbit large intestine has a segment-specific morphology and motility. However, the morphological features of the myenteric plexus, which controls intestinal motility, have not been characterized in each large intestinal segment. We investigated the myenteric plexus morphology in the rabbit large intestine using protein gene product 9.5 immunohistochemistry in whole-mount preparations. The tenial part of the first and second segments of the proximal colon had the most well developed myenteric plexus, while the caecum had the least. These findings suggest different neuronal control over the motility of each intestinal segment, thereby providing a fundamental understanding of the rabbit enteric nervous system.

Equid nutritional physiology and behavior: an evolutionary perspective

Like other members of the even-toed ungulates (the perissodactyls), equids once had a higher species diversity in the fossil record than they have today. This is generally explained in comparison to the enormous diversity of bovid ruminants. Theories on putative competitive disadvantages of equids include the use of a single toe as opposed to two toes per leg, the lack of a specific brain cooling (and hence water-saving) mechanism, longer gestation periods that delay reproductive output, and in particular digestive physiology. To date, there is no empirical support for the theory that equids fare better on low-quality forage than ruminants. In contrast to the traditional juxtaposition of hindgut and foregut fermenters, we suggest that it is more insightful to sketch the evolution of equid and ruminant digestive physiology as a case of convergence: both evolved a particularly high chewing efficacy in their respective groups, which facilitates comparatively high feed and hence energy intakes. But because the ruminant system, less based on tooth anatomy but more on a forestomach sorting mechanism, is more effective, equids depend more on high feed intakes than ruminants and may well be more susceptible to feed shortages. Arguably, the most under-emphasized characteristic of equids may be that in contrast to many other herbivores including ruminants and coprophageous hindgut fermenters, equids do not use the microbial biomass growing in their gastrointestinal tract. Equids display behavioral and morphophysiological adaptations to high feed intakes, and their cranial anatomy that facilitates the cropping of forage while performing grinding chewing at the same time might be unique. Rather than looking for explanations how equids are better adapted to their present niches than other organisms, considering them remnants of a different morphophysiological solution may be more appropriate.

No news from old drawings? Stomach anatomy in muroid rodents in relation to body size and ecology

Muroid rodents mostly have a complex stomach: one part is lined with a cornified (non-glandular) epithelium, referred to as a 'forestomach,' whereas the rest is lined with glandular epithelium. Numerous functions for the forestomach have been proposed. We collated a catalog of anatomical depictions of the stomach of 174 muroid species from which the respective non-glandular and glandular areas could be digitally measured, yielding a 'stomach ratio' (non-glandular:glandular area) as a scale-independent variable. Stomach ratios ranged from 0.13 to 20.15, and the coefficient of intraspecific variation if more than one picture was available for a species averaged at 29.7% (± 21.5). We tested relationships of the ratio with body mass and various anatomical and ecological variables, including diet. There was a consistent phylogenetic signal, suggesting that closely related species share a similar anatomy. Apart from classifying stomachs into hemiglandular and discoglandular, no anatomical or ecological measure showed a consistent relationship to the stomach ratio. In particular, irrespective of statistical method or the source of dietary information, dietary proxies did not significantly correlate with the stomach ratio, except for a trend towards significance for invertivory (insectivory). Yet, even this relationship was not convincing: whereas highly insectivorous species had high but no low stomach ratios, herbivorous species had both low and high stomach ratios. Thus, the statistical effect is not due to a systematic increase in the relative forestomach size with invertivory. The most plausible hypotheses so far associate the muroid forestomach and its microbiome with a generic protective role against microbial or fungal toxins and diseases, without evident correlates of a peculiar need for this function under specific ecological conditions. Yet, this function remains to be confirmed. While providing a catalog of published depictions and hypotheses, this study highlights that the function of the muroid rodent forestomach remains enigmatic to date. This article is protected by copyright. All rights reserved.

Metagenomic Comparisons between Soft and Hard Feces of Plateau Pikas (Ochotona curzoniae)

Simple Summary

Plateau pika produces hard and soft feces with different morphology, component and microbial structure. Hard feces had more abundant Firmicutes, while soft feces had more abundant Akkermansia. The differences of microbial communities between hard and soft feces were mainly driven by core microbomes. Soft feces had a comprehensive advances in predict functional pathways compared to hard feces, these strengthened functional pathways were closely associated with metabolism of energy, vitamins, and amino acid. Our study preliminarily explored the differences in microbial structure and function between hard and soft feces, provided a foundation for future systematic explorations of the cecotrophy.

Abstract

The division of hard and soft feces is an effective digestion strategy in the order Lagomorpha. Although previous studies have reported that hard and soft feces differ in morphology and component, the discrepancy in the microbiome remains unclear. This study explored the microbiomes of hard and soft feces in plateau pikas by sequencing the V3 and V4 regions of 16S rDNA. We found that hard feces harbored higher Firmicutes, while soft feces harbored higher Akkermansia. Increased rare bacterial taxa were observed in hard feces compared with soft feces. Moreover, hard and soft feces displayed a greater difference in terms of core operational taxonomy units (OTUs) compared to the total OTUs. The soft feces showed enhancements in all predicted Kyoto Encyclopedia of Genes and Genomes (KEGG) functions, indicating an advancing microbial metabolism compared to hard feces. The significantly upregulated pathways in soft feces were mainly enriched in metabolism of energy and carbohydrate, glycan biosynthesis, cofactors and vitamins, and amino acids—all of which are associated with increased contents of microbial proteins, vitamins, and short-chain fatty acids. Our study reports, for the first time, the differential microbiomes between hard and soft feces of pikas and provides direction for the future studies on cecotrophy.

Sand accumulation in the digestive tract of rabbits (Oryctolagus cuniculus) and guinea pigs (Cavia porcellus): The role of the appendix

We determined location and amount of accumulated sand in the gastrointestinal tract (GIT) of rabbits (Oryctolagus cuniculus) and guinea pigs (Cavia porcellus) fed diets containing external (silicate) abrasives. Computed tomographic abdominal images of rabbits (n = 44) and guinea pigs (n = 16) that each received varying numbers (4–7) of different diets for 14 days each (total n = 311 computed tomographs), and radiographs of dissected GIT and presence of silica in GIT content (n = 46 animals) were evaluated. In rabbits, the majority of accumulated sand was located in the caecal appendix, an elongated, intestinal structure in the left side of the abdomen. The ‘wash‐back’ colonic separation mechanism in rabbits may be partly responsible for a retrograde transport of sand back to the caecum, where dense, small particles accumulate in the appendix. The appendix likely acted as a reservoir of these particles, leading to significant effects not only of the momentary but also of the previous diet on recorded sand volumes in the rabbits. Guinea pigs have no caecal appendix and a colonic separation mechanism not based on a ‘wash‐back’. Less sand accumulation was found in their GIT without a specific location pattern, and there were less previous diet effects in this species. None of the rabbits or guinea pigs developed clinical signs of obstruction during the study, and the recorded sand volumes represented 1.0 ± 1.2% of the 14‐d sand intake in rabbits and 0.2 ± 0.2% in guinea pigs. Accumulation of sand in volumes up to 10 cm³ in the GIT of rabbits does not seem to cause clinical health impairment. Large inter‐individual differences in rabbits indicate inter‐individual variation in proneness to sand accumulation. The reason for the presence of a sand‐trapping caecal appendix in animals that are, due to their burrowing lifestyle and feeding close to the ground, predestined for accidental sand ingestion, remains to be unveiled.

Increasing food intake affects digesta retention, digestibility and gut fill but not chewing efficiency in domestic rabbits (Oryctolagus cuniculus)

In ruminants, the level of food intake affects net chewing efficiency and hence faecal particle size. For nonruminants, corresponding data are lacking. Here, we report the effect of an increased food intake of a mixed diet in four domestic rabbit does due to lactation, and assess changes in particle size (as determined by wet sieving analysis) along the rabbit digestive tract. During lactation, rabbits achieved a distinctively higher dry matter intake than at maintenance, with a concomitant reduction in mean retention times of solute and particle markers, an increase in dry matter gut fill, a reduction in apparent digestibility of dry matter, and an overall increase in digestible dry matter intake. By contrast, there was no change in faecal mean particle size (mean ± SD: 0.58 ± 0.02 vs. 0.56 ± 0.01 mm). A comparison of diet, stomach content and faecal mean particle size suggested that 98% of particle size reduction occurred due to ingestive mastication and 2% due to digestive processes. Very fine particles passing the finest sieve, putatively not only of dietary but mainly of microbial origin, were particularly concentrated in caecum contents, which corresponds to retention of microbes via a 'wash-back' colonic separation mechanism, to concentrate them in caecotrophs that are re-ingested. This study gives rise to the hypothesis that chewing efficiency on a consistent diet is not impaired by intake level in nonruminant mammals.

Particle size reduction along the digestive tract of fat sand rats (Psammomys obesus) fed four chenopods

It is generally accepted that microbial digestion contributes little to digesta particle size reduction in herbivores, and that faecal particle size reflects mainly chewing efficiency, and may vary with diet. Nevertheless, a decrease in mean particle size (MPS) along the gastrointestinal tract (GIT) has been reported, especially in hindgut fermenters. However, to what degree the very fine particle fraction (non-food origin, especially microbes) affects MPS is unclear. Fat sand rats (Psammomys obesus, diurnal herbivores, n = 23, 175 ± sd 24 g) consumed one of four chenopods (natural dietary items in the wild) for 30 days. Digestibility was related negatively to dietary fibre content. We determined digesta MPS in the forestomach, glandular stomach, small intestine, caecum, colon and faeces by wet sieving, including (MPS_fines) or excluding (MPS_nofines) particles < 0.25 mm. The proportions of fines were higher and of MPS_fines were correspondingly lower in GIT sections that harbour microbes (forestomach, hindgut), whereas MPS_nofines did not differ between forestomach and glandular stomach. However, MPS_nofines decreased along the GIT, indicating MPS reduction due to digestive (enzymatic and microbial) processes. The four different diets led to different MPS, but the magnitude of MPS reduction in the GIT was not correlated with dietary fibre fractions or dry matter digestibility. These results indicate that within a species, MPS cannot be used as a proxy for diet quality or digestibility, and raise the hypothesis that MPS reduction along the GIT may be more pronounced in smaller than in larger mammalian terrestrial herbivores, possibly due to the fine initial particles produced by chewing in small species.

Mammalian intestinal allometry, phylogeny, trophic level and climate

An often-stated ecomorphological assumption that has the status of 'textbook knowledge' is that the dimensions of the digestive tract correlate with diet, where herbivores-consuming diets of lower digestibility-have longer intestinal tracts than faunivores-consuming diets of higher digestibility. However, statistical approaches have so far failed to demonstrate this link. Here, we collated data on the length of intestinal sections and body mass of 519 mammal species, and test for various relationships with trophic, climatic and other biological characteristics. All models showed a strong phylogenetic signal. Scaling relationships with body mass showed positive allometry at exponents greater than 0.33, except for the caecum, which is particularly large in smaller species. Body mass was more tightly linked to small intestine than to large intestine length. Adding a diet proxy to the relationships increased model fit for all intestinal sections, except for the small intestine when accounting for phylogeny. Thus, the diet has a main effect on the components of the large intestine, with longer measures in herbivores. Additionally, measures of habitat aridity had a positive relationship with large intestine length. The small intestine was longer in species from colder habitats at higher latitudes, possibly facilitating the processing of peak intake rates during the growing season. This study corroborates intuitive expectations on digestive tract anatomy, while the dependence of significant results on large sample sizes and inclusion of specific taxonomic groups indicates that the relationships cannot be considered fixed biological laws.

Fatty Acids of Microbial Origin in the Perirenal Fat of Rats (Rattus norvegicus domestica) and Guinea Pigs (Cavia porcellus) Fed Various Diets

Guinea pigs are assumed to practice caecotrophy to a higher degree than rats. Studies from leporids suggest that through the practice of caecotrophy, hindgut fermenting species could build up microbial fatty acids (FA) in body tissues. We hypothesized that microbial FA would be detectable in the body tissue of guinea pigs and rats, and this to a higher degree in guinea pigs. Twenty-four rats and guinea pigs were fed with four different pelleted diets (lucerne-, meat-, meat-bone-, insect-based) in groups of six animals for 8 weeks. Perirenal adipose tissue differed in FA composition between the species in spite of the common diets. FA typically associated with microbial activity (saturated FA (SFA; typically 18:0), monounsaturated FA (MUFA; typically trans-fatty acids TFA), and odd- and branched-chain FA (Iso-FA)), were all detected. Guinea pigs had higher SFA levels than rats except on the lucerne diet. Concentrations of 18:0 were higher for guinea pigs on the meat and bone diet. Iso-FA concentrations in guinea pigs exceeded those of rats on all diets. FA profiles with a microbial fingerprint appear-although in low proportions-in the body tissue of both species, and this seemingly to a higher extent in guinea pigs. With respect to whether consumption of rodent meat rich in microbial FA has particular effects on human health as shown for ruminant products, microbial FA concentrations are probably too low to cause any distinct effects.

Energy requirements, length of digestive tract compartments and body mass in six gerbilline rodents of the Negev Desert

Energy requirements of an animal are size dependent and, in this study, the average daily metabolic rate (ADMR) of six Negev Desert gerbilline rodents, ranging in body mass (m_b) from 10g to over 200g, scaled to m_b^0.57. Although gerbilline rodents are considered 'granivores', these rodents consume substantial amounts of green vegetation and the largest gerbil is a strict herbivore. We predicted that the lengths of the compartments of the digestive tract would scale allometrically to mb^0.33 and that ADMR would scale allometrically to the lengths of the compartments to the exponent of 1.73. Using log-transformed data, the length of the colon scaled to m_b^0.50 (r²_adj = 0.74; p= 0.02), of the caecum to m_b^0.45 (r²_adj=0.80; p= 0.01) and of the small intestine to m_b^0.30 (r²_adj=0.59; p < 0.05). Therefore, the exponents for the colon and caecum were higher than predicted and were close to the exponent for ADMR generated for the rodents. The absolute lengths of the colon (r²_adj=0.68; p= 0.03; slope = 0.99) and of the caecum (r²_adj=0.79; p= 0.01; slope = 1.19) were related significantly to ADMR, but of the small intestine was not (r²_adj=0.04; p=0.33; slope = 0.85). The exponents implied that the relationships were isometric and not allometric as predicted and that the rates of increase of the lengths of the intestine compartments were at the same rate as the increase in ADMR. The lengths of the colon and caecum were highly correlated between each other (r²_adj=0.98; p< 0.001; slope = 1.12) and explained most of the variation in ADMR. Green vegetation could be a nutritional bottleneck for rodents as it is bulky and, consequently, limits the dietary intake, and fermentation occurs in the caecum and colon, whereas seeds, which are compact and are digested in the small intestine, would limit intake to a much lesser degree. However, when the effect of body mass was eliminated by using residuals of the variables on body mass, only the length of the small intestine was significant (r²_adj=0.86; p< 0.005; slope = -1.33) and was related negatively to ADMR. Therefore, when effects of body size were removed, most of the variation in ADMR was explained by the length of the small intestine and implied that the length of the small intestine increased with a decrease in ADMR. A higher energy expenditure was related to a shorter small intestine and, therefore, by implication, a higher concentration of metabolizable energy yield of the diet. We also questioned whether there are differences in the morphology of the digestive tract due to differences in dietary consumption. The digestive tracts of the gerbils were not diverse and could be characterized as structurally homogenous. All the gerbils had a uni-locular, hemi-glandular stomach and the differences in the digestive tract among species did not seem to be of functional importance, but rather were related to the taxon. However, some important morpho-functional characteristics of the digestive tract emerged that apply to the whole group.

Digestive physiology of captive capybara (Hydrochoerus hydrochaeris)

The capybara (Hydrochoerus hydrochaeris), the largest living rodent, probably has a "mucus-trap" colonic separation mechanism. To test this hypothesis, we measured the mean retention time of a solute marker (MRT_Solute ), 2 mm (MRT_2 mm ), 10 mm (MRT_10 mm ), and 20 mm (MRT_20 mm ) particle markers and nutrient digestibility in adult captive capybaras (27-52 kg body mass (BM), 2-11 yr). In addition, total gut fill and the selectivity factor (MRT_Solute /MRT_2 mm ) were calculated, and mean faecal particle size and metabolic fecal nitrogen of captive capybaras were compared to those of free-ranging specimens. Finally, we also measured methane production in one animal. The MRT_2 mm (29.2 ± 8.2 hr) was different (p < 0.01) from MRT_Solute (37.0 ± 13.1 hr), MRT_10 mm (36.5 ± 8.2 hr), and MRT_20 mm (35.1 ± 9.6 hr). The selectivity factor (1.26 ± 0.30) was in the range considered typical for a "mucus-trap" colonic separation mechanism. The estimated total gut fill was 1.50 ± 0.37% and 1.73 ± 0.25% of BM calculated from the results of the 2-mm and 10-mm particle markers, respectively. The CH₄ emission was 13.7 L/day. Captive capybaras had greater mean fecal particle size (0.44 ± 0.06 vs. 0.29 ± 0.05 mm, p < 0.001) and metabolic fecal nitrogen (65.5 ± 3.91 vs. 46.8 ± 10.5% of fecal nitrogen, p < 0.001) than free-ranging capybaras. Organic matter digestibility decreased less steeply with increasing dietary crude fiber content in capybaras as compared to published data from rabbits or guinea pigs. Accordingly, the digestive physiology of the capybara is characterized by a comparatively high fiber digestibility, with a "mucus-trap" colonic separation mechanism, allowing capybaras to thrive on forage-only diets.

Morphometric analysis of the gastrointestinal tract of four African muroid rodent species (Rhabdomys dilectus, Rhabdomys pumilio, Aethomys chrysophilus, and Lemniscomys rosalia)

Several muroid rodent species are distributed throughout southern Africa. Some species are reportedly classified as opportunistic omnivorous rodents consuming plant, seed, and insect material. This study aims to provide a detailed morphometric analysis of the gastrointestinal tract (GIT) of four such omnivorous species, including stomach content analysis. Fixed GIT specimens (n = 5 of each) of Rhabdomys dilectus (Mesic four-striped grass mouse), Rhabdomys pumilio (Xeric four-striped grass mouse), Aethomys chrysophilus (Red rock rat), and Lemniscomys rosalia (Single-striped grass mouse) were weighed. Length and circumference measurements of each anatomically distinct GIT region were determined to calculate the basal surface area (BSA). Histological sections from each GIT region were used to calculate a surface enlargement factor (SEF). The BSA and SEF were multiplied to calculate the luminal surface area (LSA) of each GIT region. Stomach content was analyzed both macroscopically and histologically. All species had a similar GIT morphology, namely a unilocular, hemiglandular stomach with a clear limiting ridge, which indicated the transition from stratified squamous epithelium to glandular epithelium. A large loosely spiralled cecum was present in all species. A narrowing of the cecal apex accompanied by lymph aggregates, confirmed histologically in both Rhabdomys species, indicated a cecal appendix. A single short colonic loop with a unique folding pattern for each species was present in the proximal colon. The colonic mucosal surface presented with proximal V-shaped, and distal longitudinal folds. Intermediate transitional S-shaped folds were present in three species (R. dilectus, R. pumilio, and L. rosalia). Colonic mucosal folds indicated hindgut specialization similar to other muroid rodents. The hindgut specialization was further supported by morphometric analysis, which indicated large BSA and LSA measurements in the cecum and colon. These adaptations are consistent with herbivory, despite stomach content analysis revealing omnivorous tendencies.

Direct and indirect caecotrophy behaviour in paca (Cuniculus paca)

The colonic separation mechanism in lagomorphs and some rodents, associated with caecotrophy, serves to retain microbial protein. As tropical fruits have low protein concentrations, caecotrophy could be an important microbial protein source in frugivorous rodents such as the paca (Cuniculus paca). Due to conflicting reports on the occurrence of caecotrophy in this species, we obtained digestive tracts of three adult animals and observed the behaviour of four specimens maintained on a diet of a pelleted feed (P) and a supplemental mix of fruits and sweet potato (S, a source of structural fibre). In a Latin square design, P and S were both offered either in the morning (M) or in the afternoon (A), or with one item in the morning and the other in the afternoon (SP or PS). The paca's proximal colon is characterized by a distinct furrow typical for the colonic separation mechanism of hystricomorph rodents. Caecotrophy, both "direct" (from the anus) and "indirect" (from a pile of defecated faeces), was a regular component of the paca's behavioural repertoire, and caecotrophs contained more nitrogen and less fibre than hard faeces. Higher food intake led to less overall caecotrophy. With afternoon feeding of S, the onset of caecotrophy was delayed and the proportion of indirect caecotrophy increased, with hard faeces and caecotrophs often defecated together. No indirect caecotrophy occurred on treatment M. The results suggest that the time available after ingestion of structural fibre determines the efficiency of the colonic mechanism for the separation of hard faeces and caecotrophs.

Mouse models for human intestinal microbiota research: a critical evaluation

Since the early days of the intestinal microbiota research, mouse models have been used frequently to study the interaction of microbes with their host. However, to translate the knowledge gained from mouse studies to a human situation, the major spatio-temporal similarities and differences between intestinal microbiota in mice and humans need to be considered. This is done here with specific attention for the comparative physiology of the intestinal tract, the effect of dietary patterns and differences in genetics. Detailed phylogenetic and metagenomic analysis showed that while many common genera are found in the human and murine intestine, these differ strongly in abundance and in total only 4% of the bacterial genes are found to share considerable identity. Moreover, a large variety of murine strains is available yet most of the microbiota research is performed in wild-type, inbred strains and their transgenic derivatives. It has become increasingly clear that the providers, rearing facilities and the genetic background of these mice have a significant impact on the microbial composition and this is illustrated with recent experimental data. This may affect the reproducibility of mouse microbiota studies and their conclusions. Hence, future studies should take these into account to truly show the effect of diet, genotype or environmental factors on the microbial composition.

Comparative selective retention of particle size classes in the gastrointestinal tract of ponies and goats

There is a discrepancy in the literature on potential digesta separation mechanisms in horses, with both a selective retention of fine and of large particles postulated in different publications. To assess the net effect of such mechanisms, we fed ponies on a hay-only diet a pulse dose of whole (unchopped) marked hay together with a solute marker, collected faeces on a regular basis, measured marker concentrations in whole faeces and in their large (2.0-16 mm), medium (0.5-1.0 mm) and small (0.063-0.25 mm) particle fraction, and calculated the corresponding mean retention times (MRTs). For comparison, the same experiment was performed in goats. In goats, as expected, MRT_solute (35 hr) was significantly shorter than MRT_particle (51 hr); only a very small fraction of particle marker was excreted as large particles (2%); and the MRT of these large particles was significantly shorter than that of small particles (with a relevant difference of 8.6 hr), indicating that those few large particles that escape the rumen do so mostly soon after ingestion. In ponies, MRT_solute (24 hr) did not differ from MRT_particle (24 hr); a higher fraction of particle marker was excreted as large particles (5%); and the MRT of these large particles was longer than that of small particles (but with a non-relevant difference of less than 1 hr). These results indicate that no relevant net separation of digesta phases occurs in horses and that selective particle retention mechanisms in the large intestine are unlikely to represent important characteristics of the horse's digestive physiology.

Comparative gastrointestinal morphology of Tachyoryctes splendens (Rüppell, 1835) and Heliophobius emini, (Noack, 1894) two species of East African mole-rats

Tachyoryctes splendens (Northeast African mole-rat) and Heliophobius emini (Emin's mole-rat) are two African mole-rats that represent separate allopatric rodent families namely Spalacidae and Bathyergidae respectively. While these species consume a similar diet of underground plant storage organs such as roots and tubers, T. splendens has been reported to additionally consume small amounts of aerial foliage. This study aims to provide detailed gross morphological and histological morphometric analyses of the gastrointestinal tract (GIT) of these two subterranean species. The formalin fixed gastrointestinal tracts of T. splendens (n = 9) and H. emini (n = 6) were photographed, weighed and measured. The length and basal surface areas were calculated for each anatomically distinct region. Representative histological samples were prepared and stained using Hematoxylin and Eosin. Microscopic luminal measurements were used to calculate a surface enlargement factor and the luminal surface area of each region. Tachyoryctes splendens had a large double chambered hemi-glandular stomach with a macroscopically visible transition from keratinized stratified squamous epithelium to glandular epithelium. The cecum was large and the luminal surface revealed a single spiral fold. The ascending colon of T. splendens was arranged in a spiral, with two centripetal and two centrifugal windings. The descending colon was arranged in a single parallel loop, similar to H. emini. A narrow colonic groove was accompanied by V-shaped folds on either side. Heliophobius emini had a simple glandular stomach, a large, haustrated cecum that displayed a cecal appendix and the descending colon was arranged in a single parallel loop. The internal aspect of the colon revealed a wide colonic groove extending from the ceco-colic junction to distal colon. As both species originate from a similar geographical region and ingest very similar diets, it is likely that the differences in the GIT morphology are attributed to phylogeny as the species represent two different families of mole-rats.

Fecal nitrogen concentration as a nutritional quality indicator for European rabbit ecological studies

Measuring the quality of the nutritional resources available to wild herbivores is critical to understanding trophic regulation processes. However, the direct assessment of dietary nutritional characteristics is usually difficult, which hampers monitoring nutritional constraints in natural populations. The feeding ecology of ruminant herbivores has been often assessed by analyzing fecal nitrogen (FN) concentrations, although this method has been less evaluated in other taxa. This study analyzed the suitability of FN as an indicator of ingesta quality in the European rabbit (Oryctolagus cuniculus), which is a keystone lagomorph species in Mediterranean ecosystems and of great conservation interest. Firstly, domestic O. cuniculus were used to evaluate under experimental conditions the accuracy of total FN and the metabolic FN as diet quality indicators of forages with characteristics similar to those available under natural conditions. Secondly, the accuracy of Near-Infrared Spectroscopy (NIRS) to calculate FN was tested using partial least squares regression. Thirdly, a pilot field study was conducted to monitor FN dynamics from wild O. cuniculus in three different habitats during wet and drought periods. A strong association was found between diet type and total FN and metabolic FN (Pseudo-R(2) ≥ 0.89). It was also found that NIRS calibrations were accurate for depicting nitrogen concentrations (R(2) > 0.98 between NIRS and chemical results). Finally, the seasonal FN dynamics measured in the field were consistent with current knowledge on vegetation dynamics and forage limitations in the three habitats. The results support the use of NIRS methods and FN indices as a reliable and affordable approach to monitoring the nutritional quality of rabbit habitats. Potential applications include the assessment of the mechanistic relationships between resource limitations and population abundance, e.g., in relation to natural drought cycles and to habitat interventions aimed at reinforcing rabbit populations.

Rodent nutrition: digestive comparisons of 4 common rodent species

This article summarizes the literature regarding digestive strategies and captive diets of common rodent pocket pets. A comparison is made between the 2 suborders in which chinchillas, guinea pigs, hamsters, and gerbils occur, highlighting digestive anatomy and dietary adaptations. Recommended captive diets are provided, as well as common nutritionally related health issues that may be presented to veterinary clinics.

Gastrointestinal anatomy and physiology of select exotic companion mammals

The anatomy and gastrointestinal physiology of rabbits, guinea pigs, and chinchillas are different from those of other exotic companion mammals. Rabbits, guinea pigs, and chinchillas are all concentrate selectors, hindgut fermenters, and coprophagic. They are designed to intake large quantities of high-fibrous, low-energy-density foods. They use unique colonic separation mechanisms and have open-rooted, constantly growing dentition. Gastrointestinal disease, often secondary to diet or environmental factors, is common in these species.