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BACKGROUND: The dromedary camel and the oryx antelope are exposed to excessive heat and solar radiation in their desert habitat. Desertification of areas with by now little rainfall may occur eventually. Well-adapted large animal species show us what is needed to survive in scorching regions.

METHODS: Four scimitar-horned oryx antelopes (Oryx dammah), 10 camels (Camelus dromedarius), nine South African Merino sheep, and 17 Nguni cows were tested for RBC aggregation, RBC elongation, and plasma viscosity. The temperature dependency of blood viscosity was tested in 10 camels and compared to human reference values.

RESULTS: Unlike sheep, Nguni cow, and dromedary camel, oryx RBCs aggregate in native plasma (M0:5.2 (3.3/6.7); M1:18.1 (16.7/27.9); Myrenne MA1). Elongation indices of oryx RBCs were intermediate to low (EImax: 22.6 (19.2/25.3); SS1/2 3.67 (2.52/4.95); Rheodyn SSD). Camel RBCs did not display the typical SS/EI curve by rotational ektacytometry. In-vitro blood viscosity (Physica MCR302) was lower in camels than in human blood at equal hematocrit. A decrease of temperature had only little effect on camel blood. At 10 s(-1), blood viscosity in camel increased from 2.18mPa*s (2.01/2.37) at 42 degrees C to 4.39mPa*s (4.22/4.51) at 12 degrees C. In human blood, viscosity ranged from 8.21mPa*s (6.95/8.25) at 37 degrees C to 15.52mPa*s (14.25/16.03) at 12 degrees C. At 1000 s(-1), blood viscosity in camel ranged from 2.00mPa*s (1.95/2.04) at 42 degrees C to 3.98mPa*s (3.88/4.08) at 12 degrees C. In human blood, viscosity ranged from 5.35mPa*s (4.96/5.87) at 37 degrees C to 11.24mPa*s (10.06/11.17) at 12 degrees C.

CONCLUSIONS: Desert ungulates may need RBC membranes, which are fortified to withstand changes in osmolality during dehydration-rehydration cycles. This reduces RBC deformability. Dromedary camel blood does not undergo stark changes in viscosity with changes in temperature. Therefore, blood fluidity could be rather maintained during the day and night cycle. This should reduce the need of the vascularity to rhythmically adapt to changing shear forces when camels experience heterothermy.