[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 Ochotonapallasi 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.

[Role of microbiocenosis of the gastrointestinal tract in the nutrition of grouse].

In order to assess the role of the microbiocenosis of the digestive tract of herbivorous birds in transforming poor forage, the activity of cellulolytic enzymes in all departments of the gastrointestinal tract of the black grouse (Lyrurus tetrix) and Western capercaillie (Tetrao urogallus) was studied. The functional diversity of microbial communities of different departments was also investigated. In both species of birds, nitrogenase and cellobiohydrolase activities were discovered in the digestive tract, with the maximum observed in the cecum.

[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.

[Morphological provision for the specialization of hares to coprophagy: the architectonics of the mucous surface of the intestine].

The macro- and microstructures 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.

[Reduction of plant fibers in the digestive tract of the moose and the red deer].

A comparative study of the reduction of plant fibers moving in the digestive tract of nine red deer (Cervus elaphus) and six moose (Alces alces) was made. In the winter season, the character of fiber reduction in the moose and the red deer was similar. In the deer obtained in the early autumn, the relative concentration of small-sized fractions was significantly higher. A sharp decrease in the share oflarge-sized fibers was observed in the omasum as compared to the rumen and the reticulum. It was especially pronounced in the deer obtained in September. Deceleration of fibers of large-sized fractions in the rumen and the reticulum and the structure of the reticulo-omasal opening and its functions were considered.

[Functional features of microbial communities in the digestive tract of field voles (Microtus rossiaemeridionalis and clethrionomys glareolus)].

The nitrogen-fixating and cellobiohydrolase activity, the nitrogen (N) and carbon (C) contents, and the number of microorganisms in the prestomach, cecum, and colon of two vole species were studied: the southern vole (Microtus rossiaemeridionalis) and the bank vole (Clethrionomys glareolus), which is characterized by a mixed type of diet. The nitrogen-fixating activity in the cecum was found to be the highest in the voles compared with the mammals studied earlier. The seasonal dynamics of both nitrogenase and cellobiohydrolase activities was registered in the southern vole. The structure of the microbial complex in the southern vole is more varied and includes microorganisms associated with plant substrates.

[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 keratinizing epithelium is variable and depends greatly on the type of stomach filling and distribution of food mass in it. The bordering fold and ileocecaljunction 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.

[Microbial nitrogen fixation in the gastro-intestinal tract of Kalmykia gerbils (Meriones. tamariscinus and Meriones meridianus)].

The nitrogen-fixing activity, nitrogen (N) and carbon (C) contents, and the number of microorganisms in the forestomach, cecum, and segmented intestine were detected in two gerbil species, granivorous Meriones meridianus and M. tamariscinus, which consume a large amount of green parts of the plants. M. meridianus had higher levels of nitrogen-fixation activity in all investigated parts of the gastro-intestinal tract compared with M. tamariscinus. The highest levels were detected in the colon of M. meridianus. The C/N ratios in the forestomach of M. tamariscinus were higher than in M. meridianus, which is consistent with the greater role of the green parts of plants in its diet. A gradual increase in the nitrogen content from the forestomach to the colon of M. tamariscinus was noted. The amount of microorganisms in the forestomach and intestine of the studied gerbil species was similar.

[Assimilation of biological nitrogen by European beaver].

Nitrogenase activity, the abundance of diazotrophic bacteria, the structure and functional characteristics of the complex of microorganisms, and the content of nitrogen and carbon were determined in the contents of the gastrointestinal tract of the European beaver. A high nitrogen-fixing activity in the large intestine correlated with an increase in nitrogen content in the chyme upon its transfer over the gastrointestinal tract. It is assumed that microbial nitrogen fixation plays a major role in nitrogen nutrition of the European beaver.

[Feeding rate of sibling vole Microtus rossiaemeridionalis and Mandarin vole Lasiopodomys mandarinus].

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.

[Effect of deficiency of dietary nitrogen on cellulose digestibility and nitrogen-fixing flora activity in the sibling vole Microtus rossiaemeridionalis]. / Vliianie defitsita dietarnogo azota na perevarimost' tselliulozy i aktivnost' azotfiksoruiushchei microflory u vostochnoevropeiskikh polevok Microtus rossiameridianalis.

The effect of food composition on nitrogen-fixing activity of the symbionts living in the digestive tract of the sibling vole Microtus rossiaemeridionalis was experimentally studied. In the control, the rodents were allowed to select any of three food mixes: protein-rich, protein-free with low cellulose content, and protein-free with high cellulose content. The voles consumed the food in a proportion corresponding to 16% of protein and about 6% of cellulose. Exclusion of the protein-rich food considerably increased cellulose consumption (up to 12%) and digestibility (from 35 to 64%). The changes in the consumed food composition were reflected in localization of nitrogenase activity in the digestive tract: the control level of nitrogen-fixing activity in the cecum was three times that in the proventriculus, while an inverse proportion was observed in the experimental groups. In all cases, the colon was the major locus of nitrogen fixation.