Vitamin E in cranes: Reference ranges and nutrient interactions
Fat soluble vitamins E and A (quantified as α-tocopherol and all-trans retinol, respectively) were measured in plasma samples from 274 captive cranes from four institutions and five free-ranging birds. Ages ranged from 4 mo to 80 yr, and all 15 crane species were represented. Captive cranes had a mean ± standard error (SE) of 6.57 ± 0.82 μ g/ml α -tocopherol; migrating greater sandhill cranes ( Grus canadenis tabida ) had a plasma concentration of 3.71 ± 0.22 μ g/ml. Sex and age differences were not significant, but crane species that evolved in temperate habitats had higher circulating levels of α -tocopherol than tropical or subtropical species. Mean ± SE retinol values were 0.69 ± 0.05 μ g/ml in captive cranes, and 0.66 ± 0.08 μ g/ml in free-ranging cranes; values did not differ significantly by sex, age, or species. Dietary vitamin E concentrations were significantly correlated with plasma α -tocopherol levels in a logarithmic relationship. Dietary selenium at 0.5 mg/kg was associated with decreased circulating a-tocopherol concentrations.