Caecal villi? A comparative histological and morphometric study of caecal and jejunal mucosa in adult rabbits

Abstract

Rabbits are herbivores with a distinctive digestive strategy that differs significantly from other caecal fermenters (e.g., horses, guinea pigs) and ruminants. In view of this, the current study aimed to highlight distinctive histological and morphometric features of the caecal mucosa in adult rabbits that accentuate its major role in digestion. The caecal and jejunal samples were harvested from five 1-year-old domestic rabbits and processed by regular paraffin-embedding histological technique followed by Goldner’s trichrome staining. A comprehensive morphological and morphometrical analysis of the jejunal mucosa vs. caecal mucosa was performed. Microscopically, as in the case of the jejunal mucosa, the caecal mucosa presents long and often branched finger-like villi covered by a simple columnar epithelium mostly made of enterocytes with a prominent microvillous brush border. Besides, the caecal villi include a lacteal along with the villous muscle. Statistically, except for villus length, all the parameters assessed in the caecal mucosa, including villus width, villus count, thickness of the brush border and enterocyte/goblet cells ratio, revealed a high grade of similarities with the jejunal villi. According to the obtained results, the caecal mucosa in adult domestic rabbits includes unique features, namely caecal villi, structures infrequently presented in the large intestine of other adult mammals. Those structures once more emphasize the major role of the caecum not only in fermentation but also subliminally in local absorption. To our knowledge, this is the first reliable microanatomical and morphometric report of caecal villi in adult domestic rabbits.