G. K. Zharova

Isolating structures of gerbils’ digestive tract (Gerbillidae, Rhombomys, Meriones) and their functional significance

The morphology of the digestive tract of three species of gerbils characterized by different food specialization—Rhombomys opimus, Meriones tamariscinus and M. meridianus—is considered. The correlation between areas of glandular and cornified epithelium is variable and depends greatly on the type of stomach filling and distribution of food mass in it. The bordering fold and ileocecal junction is not only able to isolate the forestomach and caecum significantly but also may be a mechanism of regulation of food movement through the digestive tract. The close location of ileum’s opening to the caecum and its outlet to the colon, as well as isolation of caecum’s cavity by a circular fold, could provide direct food transit from the ileum to the colon.

Interrelation between size of body and of digestive tract organs in some myomorpha: Isometry or allometry?

Using nonparametric tests, we analyzed the weights of the digestive tract organs of 198 rodent individuals belonging to 11 species of Arvicolinae (family Cricetidae) and Murinae (family Muridae), using both fresh and fixed material, the weight characteristics of which were identical. It has been shown that no unique dependence exists between the body weight and the entire digestive tract one in Arvicolinae rodents weighing 8–73 g. It was also shown that interspecific differences in the relative mass of such a dynamic system of organs as the digestive system cannot always be regarded as a function of the body size alone.

Concentration and size distribution of plant fiber in the digestive tract of muroid rodents

The weight parameters that characterize the size and the degree of fullness of fermentation chambers (forestomach and cecum), namely, the weight of the walls and the content of these organs, and the concentration and size distribution of fibers in the chyme have been investigated in five muroid rodent species (Arvicola terrestris, Microtus oeconomus, Microtus arvalis sp., Clethrionomys glareolus, and Sylvaemus flavicollis). No distinct regularities were observed in the above-mentioned parameters of the forestomach. These parameters of the cecum were generally found to be in good agreement with the conventional concept of dietary specialization of the rodent species under investigation, but the results have provided a more precise assessment of the role of dietary fiber in the diet of free-living rodents under specific environmental conditions.

Morphological provision for the specialization of hares to coprophagy: The architectonics of the mucous surface of the intestine

The macrostructure of the surface of the mucous membrane of the gastrointestinal tract were studied in detail in two hare species (Lepus europaeus and L. timidus) using scanning electron and digital microscopes. The morphology of the gastrointestinal tract of hares, which is similar in the two species studied, was described in detail. The macrostructure of the inner surface of the ileocecal junction was investigated. The particularities of the architectonics of the mucous membrane of the intestine that are specific for hares were revealed. In the jejunum of both hare species, the mucous membrane is represented by villi with merged bases, which form circular plates. The mucosa of the colon forms large conical villi, the surface of which is scattered with secreting cells. The possible functional significance of the revealed morphological particularities is discussed.

Feeding rate of sibling vole Microtus rossiaemeridionalis and mandarin vole Lasiopodomys mandarinus housed in cages and enclosures

Consumption of food of different nutritive value by sibling vole Microtus rossiaemeridionalis and mandarin vole Lasiopodomys mandarinus as a function of housing conditions—in cages or enclosures—was comparatively studied. Experimental groups included 8–14 adult non-reproducing animals of both sexes kept one per cage or enclosure. The rate of food consumption and digestibility were studied by standard methods and the obtained data were statistically analyzed using Statistica 6.0. Significant differences in the rate of food consumption by mandarin voles housed under different conditions as well as in the consumption and digestibility of food of different biochemical composition in both vole species have been revealed.

Degradation of cellulose fibers in the digestive tract of Microtus voles

It is important for effective utilization of plant food by specialized phytophagous mammals that they finely crush it with their teeth. Careful chewing (or rumination, i.e., chewing cud) substantially increases the accessibility of structural carbohydrates, which constitute a considerable part of plant food, for bacterial fermentation and shortens the retention of food in the digestive tract, thereby increasing its utilization. The dependence of fermentation rate on the sizes of food particles in cattle has been demonstrated experimentally with the use of in vitro and in sacco methods [1].

The effect of coprophagy on the size of plant fibers in the digestive tract of hares Lepus europaeus and L. timidus (Lagomorpha, Leporidae)

We have studied the distribution of plant fibers of different sizes in the digestive tracts of two hare species: the brown hare (Lepus euopaeus) and the mountain hare (L. timidus). In all studied hares (18 specimens), the highest amount of fine-sized fibers (less than 0.25 mm length) was observed in the cecum (50–70% of the total fiber mass). It was found out that the fine-sized content in the digestive tract, and especially in the cecum, is provided not only by the separation mechanism of the colon, but also by coprophagy. It was shown that repeated passage of food through the digestive tract compensates small volume of the cecum and increases the period of digestion of the same portions of food.

Reduction of plant fibers in the digestive tract of two pika species (Ochotona pallasi and O. dauurica, Lagomorpha, Ochotonidae)

The distribution of fibers of different sizes in the gastrointestinal tract in two species of pikas—Pallas’ pika Ochotona pallasi and daurian pika O. dauurica—was studied. It was established that fibers of small-sized fractions dominated in all organs of the digestive tract of both pika species, the proportion of which in the stomach proved to be even higher than in fine-grinding voles. No distinct changes in the composition of the size fractions of fibers from organ to organ were observed in the studied individuals of both species, which may be due to frequent consumption of finely dispersed cecotrophs by pikas, which enrich the primary chewed food with small fibers.

The structure of the epithelial surface of the gastrointestinal tract of Pikas (Ochotona pallasi and O. dauurica, Lagomorpha, Ochotonidae): Functional and species specificity

The macro- and microrelief of the surface of the digestive tract mucosa of two pika species—Pallas’s (Ochotona pallasi) and Daurian (O. dauurica)—were studied in detail using whole-mount preparations and scanning electron microscopy. The structural features of the intestinal mucosal surface specific of mammals, such as the formation of projections on the crest of the cecal spiral fold and microcells in the colonic ampulla, were studied. It was found that the colonic mucosa forms sparse large conical villi in pocket cavities and on the surface of muscle bands. Significant differences in the cecal mucosal relief were found between the species studied. The possible functional significance of the identified morphological features is discussed.

Functional and Size Characteristics of the Digestive Tract of the Mole Vole Ellobius talpinus

The weight parameters of the digestive tract, which characterize the size and filling of the fermentation chambers (forestomach and cecum), the mass of the walls and of the content of these organs, and the concentration and size composition of the fibers in the chyme have been determined in 12 individuals of the mole vole Ellobius talpinus born in captivity. The uneven development of the organs of the digestive tract of the mole vole is associated with the specificity of food specialization and does not serve as a compensatory mechanism. Large-size fractions of fiber masses dominate in the content of all organs; the specific content of the fibers is much lower in comparison with M. arvalis sp., which reflects the small impact of cellulose in the feeding of the mole vole. The bilocular discoglandular stomach of the mole vole, which is also typical for herbivorous rodents, is adapted to assimilate easy digestible fodder.