Morphometric and immunohistochemical study of the reticulum of red deer during prenatal development

Iberian red deer need to be conserved for their economic role and for their genetic importance as an important component of the ecosystem. Modifications currently being made to traditional management systems require a better understanding of the structure, function and development of their alimentary system. Here we describe a histomorphometric and immunohistochemical analysis of the stomach of 25 red deer embryos and fetuses from 30 days of gestation until birth (235 days). Differentiation of the reticular compartment from the primitive gastric tube begins at 67 days, forming a three‐layered structure: epithelium, pluripotential blastemal tissue and serosa. The primitive reticular cells are initiated as small epithelial evaginations (primary ribs) at 117 days. At 142 days, lateral growths appear from the primary reticular ribs, forming the corneum papillae. The secondary reticular ribs form at 142 days as growths from the primary ribs. The uneven height of primary and secondary reticular ribs leads to the formation of cells of varying size. Growth of the reticular ribs involves the lamina propria but not the submucosa, so clear separation of these layers is maintained during histodifferentiation. Formation of the tunica muscularis from the pluripotential blastemal tissue begins at 67 days of intrauterine life, as two layers of longitudinally and circularly arranged myoblasts. Differentiation of the muscularis from the mucosa occurs at approximately 205 days, as longitudinal projections of the internal bundles of the tunica muscularis form the musculature of the primary ribs. The secretion of neutral and acid mucopolysaccharides by the reticular epithelial layer begins at 67 days, establishing the gradual adaptation of the mucosa to its protective function in postnatal life. Neuroendocrine (non‐neuron enolase) and glial cells (glial fibrillary acidic protein and vimentin) were detected by immunohistochemistry, in a similar localization and intensity to that reported in the rumen. The neuropeptides vasoactive intestinal peptide and neuropeptide Y showed a positive immunoreaction in the reticular epithelium from 142 days of prenatal life, again earlier than reported for the rumen. In comparison with domestic ruminants, deer were shown to be less precocious with regard to development of gastric tube, in their capacity to secrete neutral mucopolysaccharides, and in their neuroendocrine nature, as determined by the detection of positive neuroedocrine and/or glial cells.