The surface morphology of the omasum of the African goat.

The microstructure of the omasum of the African goat was investigated macroscopically, as well as by scanning electron microscopy to determine how the omasum is anatomically specialised to enable the goat to graze and browse so successfully in the harsh environments of Africa. The omasum of the African goat was found to be more simple in structure than that of other domesticated ruminants. The omasal laminae were arranged in only 3 orders with the number of laminae varying between 27 and 33, considerably fewer than previously described for other goats, sheep or cattle. The large conical and unguiculiform papillae surrounding the reticulo-omasal orifice, as well as the hooked papillae present on the laminae, were more similar to those of wild ruminants that browsed than domestic grazing species. The papillae on the laminae were also found to be directionally orientated towards the orifices, which may suggest a "sieve mechanism' at the reticulo-omasal orifice and interlaminar spaces. In addition, it may suggest a directional movement of ingesta between the laminae. The stratified squamous epithelium lining the laminae and papillae was lightly keratinised which, along with the microplicae-like surface folds and pits of the superficial cells, indicated that it was functionally structured for absorption. These morphological specialisations of the omasal surfaces of the indigenous African goat demonstrated similarities with that of wild ruminants that are able to graze and browse.