Assessment of physiological adaptation of indigenous and crossbred cattle to hypoxic environment in Ethiopia

High altitude pulmonary hypertension is common in cattle at high altitude areas. The extent of proneness, epidemiology, and genetics of the disease is not, however, known in Ethiopia where a large proportion of the area is at altitudes above 2700m. To learn about adaptive characteristics of cattle towards altitude, a study of physiological adaptation, measured via pulmonary artery pressure (PAP) score from 218, hematological parameters from 672, and arterial oxygen saturation predicted by pulse oximeter from 241 animals was conducted in North Western Ethiopia. Local breeds and their crosses with Holstein Friesian and Jersey were investigated. Results showed that all PAP scores (21 to 47mm Hg) fall under low to moderate risks. No sign of pulmonary hypertension was observed among all the cattle genotypes. Crosses of the local cattle with Holstein Friesian and Jersey were not more prone to the disease than local cattle. A statistically significant (P<0.05) decrease in the percent arterial hemoglobin oxygen saturation (% SaO₂) to approximately 82% was present in the high altitude animals. Crosses and locals at high altitude, ≥2700m, did not exhibit significant differences (P>0.05) in % SaO₂. We report a new clinically relevant range of oxygen saturation, ≥68%, for the high altitude cattle which is far below the threshold value usually assumed for temperate cattle, >80%. Hematological values of the studied genotypes lie within normal ranges set for temperate breeds despite suffering from heavy parasitic infestation. The significantly greater (P<0.001) red blood cell counts, hemoglobin and hematocrit values of Simien cattle measured at 3500m compared to the other genotypes in this study were not different when compared to other breeds studied elsewhere at lower altitudes and around sea level. Simien cattle probably have unique adaptations of oxygen uptake and delivery that result in the absence of hypoxemic stimulus to increase red blood cell production and hemoglobin concentration. We concluded that indigenous cattle of the Simien Plateau of Ethiopia are adapted genetically to high altitude by largely eliminating the hypoxic pulmonary vasoconstrictor response. The good adaptation is most likely due to natural selection. Understanding this adaptation model requires investigation of the biological mechanisms and the underlying genetics.