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We assessed the effects of a long and severe period of underfeeding, followed by a rapid refeeding with a high-concentrate diet, on weight, protein mass, and cellularity of the splanchnic organs in adult ewes. Twenty-four ewes, allocated to four groups of six, were fed a forage diet (50% regrowth of natural grassland hay and 50% wheat straw) either at maintenance (groups M and MO) or at 40% maintenance (groups U and UO) for 78 d. Groups M and U were then slaughtered, and groups MO and UO were subsequently overfed a high-concentrate diet (52% hay, 20% barley, 16% rapeseed meal, 4% fish meal, and 8% Megalac) at 236% maintenance for 26 d before being slaughtered. During the experiment, feed was adjusted to maintain feed supply at a constant percentage of animal requirements. After slaughter, fresh weight, dry weight, and protein mass of the reticulorumen, omasum, abomasum, small intestine, large intestine, and liver were measured. Cellularity was assessed from nucleic acids and protein contents for both ruminal mucosa and muscular-serosa layers, jejunum, and liver. The concentrations of ubiquitin and cathepsin D mRNA were measured in ruminal mucosa and muscular-serosa layers and in jejunum. Underfeeding decreased protein mass of splanchnic organs, especially in liver (-29%) and reticulorumen (-39%). Refeeding previously underfed animals increased protein mass of liver (+102%) and small intestine (+59%). No carry-over effect of the previous level of intake (UO vs. MO) was observed on the protein mass of splanchnic tissues after 26 d of refeeding. Variations in liver mass were mainly due to hypertrophy, as determined by the protein:DNA ratio, whereas variations in small intestinal mass were mainly due to hyperplasia, as determined by the amount of DNA. By contrast, changes in rumen mass associated with increasing ME intake seemed to be related to hypertrophy in the muscular-serosal component and hyperplasia in the epithelial component. The concentrations of ubiquitin and cathepsin D mRNA in the rumen and jejunum were not modified by feeding level, demonstrating that the expression of these genes for proteolytic enzymes was unchanged under these conditions.

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The specific motility patterns of the forestomach of ruminants, composed of three structurally distinct compartments (rumen, reticulum, omasum), require an elaborate intramural innervation. To demonstrate the complex structure of the enteric nervous system (ENS), whole mount preparations obtained from different sites of the bovine forestomach were submitted to immunohistochemical procedures in which neuronal (protein gene product 9.5, neurofilament 200) and glial (protein S-100, glial fibrillary acid protein) markers were applied. Immunohistochemistry performed on whole mounts allowed a detailed two-dimensional assessment of the architecture of the intramural nerve networks. Generally, the myenteric and submucosal plexus layers were composed of ganglia and interconnecting nerve fiber strands, whereas the mucosal plexus consisted of an aganglionated nerve network. However, the texture of the ENS showed considerable regional differences concerning the ganglionic size, shape and density and the arrangement of nerve fiber strands. The myenteric plexus of the ruminal wall, showing a low ganglionic density and wide polygonal meshes, contrasted with the nerve network within the ruminal pillar which consisted of ropeladder-like nerve fiber strands and parallel orientated ganglia. The highest ganglionic density was observed at the reticular groove, the most prominent ganglia were found within the omasal wall. Branches of the vagal nerve frequently ramified within the myenteric plexus layers. The submucosal plexus of the rumen was divided into an external and internal layer; the reticular submucosal plexus followed the cristae and cellulae reticuli, the omasal submucosal (sublaminar) plexus showed intra- and parafascicular ganglia apart from ganglia located at the junctions of the nerve network. The mucosal plexus of the rumen consisted of thin nerve fascicles ramifying between the ruminal papillae, and reticular mucosal nerve fibers passed throughout the base of the cellulae reticuli. The highly specialised nerve network of the intralaminar omasal plexus showed radial and transverse trajectories reflecting the spatial arrangement of the intralaminar musculature. The demonstrated structural complexity of the ENS reflects the functional complexity of the ruminant forestomach and indicates the relatively high degree of autonomy in coordinating the different motility patterns required for the processing of the ingesta.

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The histogenesis of the ruminal mucosa was studied in 9 buffalo fetuses (CRL 90--730 mm) and one suckling female buffalo calf. The Lamina epithelialis was found to consist of a basal and superficial layer. The former consists firstly of 2--4 cell layers and becomes later reduced to only one, made up to columnar cells; the latter one consists firstly of about 9 cell layers and increases then to 28--35, depending on the ruminal compartment. The epithelium shows its embryological feature, i.e. all nuclei are directed to the luminal cell pole. The first incidence of the ruminal papillary formation in the Egyptian water buffalo is observed in fetuses of 170 mm CRL. The histogenetic steps of the formation of the ruminal papillae are the aggregation of the cells of the basal layer and of the Lamina propria; the undulations with involvement of the basal layer of the Lamina epithelialis, basement membrane and Lamina propria; formation of humps from the undulations; formation of papillae. The papillary primordia are seen first in the Atrium ruminis and in the caudoventral blind sac simultaneously. The suckling calf has still no definite ruminal papillae. Only their tips are projecting to a different extent into the lumen.

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