Functional anatomy of the omasum in high arctic svalbard reindeer (Rangifer tarandus platyrhynchus) and Norwegian reindeer (Rangifer tarandus tarandus)

The structure and fill of the omasum was investigated in summer and in wint er in adult female reindeer living on the polar desert and tundra of the hi gh Arctic archipelago of Svalbard and in sub-Arctic mountain habitats in no rthern Norway. The mean total mass of the omasum in non-lactating adult fem ale Svalbard reindeer was 467 g (0.65 g per 100 g live body mass (BM)) in S eptember and 477 g (1.03 g per 100 g BM) in April. By contrast, the mean ma ss of the omasum in non-lactating adult reindeer in northern Norway was 534 g (0.83 g per 100 g BM) in September but only 205 g (0.35 g per 100 g BM p <0.05) in late March, owing to a decrease in both tissue mass and the wet m ass of the contents of the organ. The mean absorptive surface of the omasum in Svalbard reindeer was 2300 cm(2) in September and 2023 cm(2) in April. In Norwegian reindeer, by contrast, the absorptive surface area decreased f rom 2201 cm(2) in September to 1181 cm(2) (p<0.05) in late March. The marke d seasonal decline of omasal tissue and contents in Norwegian reindeer prob ably results from intake of highly digestible forage plants, including lich ens, in winter. Svalbard reindeer, a non-migratory sub-species, survive eat ing poor quality fibrous vascular plants in winter. The absence of any mark ed seasonal change in the mass, total absorptive surface area or filling of the omasum in Svalbard reindeer in winter despite a substantial decline in body mass presumably reflects their need to maintain maximum absorption of nutrients, including volatile fatty acids, when feeding on such poorly fer mentable forage.