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| Location: |
World |
| Subject: |
Physiology |
| Species: |
All Rhino Species |
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Previous work in our laboratory and others has shown differences in plasma alpha-tocopherol levels between zoo (0.2 micrograms/mi) and free-ranging (0.8 micrograms/ml) black rhinos. Because this is a measure of vitamin E activity, the result suggested that many captive animals may be suffering from vitamin E deficiency. 'Re original comparison was made with 31 blood samples taken during a 1988 translocation exercise in Zimbabwe. Later we measured plasma alphatocopherol in samples from 44 free-ranging black rhinos in South Africa, 7 in Kenya, 4 in Namibia, and an additional 24 animals in Zimbabwe. The results averaged 0.6, 0.2, 0.8 and 0.5 micrograms/ml respectively.
Because plasma and dietary levels of alpha-tocopherol are closely correlated, the differences seen among these various rhino populations suggested widely varying diets and/or habitat quality. To investigate this possibility, a collaborative field study with Fred K. Waweru, Wildlife Conservation International, Kenya, R. DuToit, Zambezi Rhino Project, and R. Brett, World Wildlife Fund, Kenya, was organized to quantify alpha-tocopherol levels in major browse species consumed by black rhinos. Two national parks and two private reserves in Kenya, and the Zambezi Valley, Zimbabwe, were chosen as study sites.
Tocopherols must be extracted from fresh plant tissues, and, to our knowledge, have not before been measured in a field study. In order to do so, a portable laboratory containing necessary chemicals and a hand-held homogenizer, as well as a full-sized tank of nitrogen gas, was loaded into vehicles and taken to makeshift labs. Converted storerooms or kitchens generally met our relative minor requirements of bench space, electricity and water, although we were treated to a proper laboratory at the Rukomechi Tsetse Fly Research Station in the Zambezi Valley! Samples were weighed, homogenized, extracted, evaporated, reconstituted, sealed, and freezer-stored until shipment back to the United States for high-performance liquid chromatography analysis.
Ale experienced African field researchers identified a minimum of ten species of major food plants for each site. Results indicated wide variation in vitamin E levels in fresh rhino browse plants. Leaves contained two to fifty times more alpha-tocopherol than stem fractions of the same plant; mature tissues had higher concentrations than young, growing tissues. Environmental variables appeared to influence vitamin E levels in browse significantly, but were not taken into account in this preliminary study. Rainfall, temperature and sunlight effects on alpha-tocopherol metabolism in plants are currently being examined in controlled greenhouse studies.
Whole plants ranged from 4.1 (Acacia drepanolobium) to 420.9 (Scutia myrtinus) mg alpha-tocopherol per kg dry matter which is equivalent to 6-630 International Units of Vit- amin E activity/ kg (1 mg = 1.49 IU). Dietary levels of alpha-tocopherol from various locations (unweighted means) did not correlate well with the plasma levels previously measured in animals from the various sites. For example, the twenty-seven Zambezi Valley plants averaged 45.5 mg/ kg alpha-tocopherol (range 6.4 to 191.8) whereas the Kenyan location, which had the animals with lowest plasma alpha-tocopherol, averaged 154.2 (range 21.2 to 420.9). Reasons for this apparent discrepancy are being investigated.
Nonetheless, about 60% of the plants sampled contained vitamin E levels greater than 50 IU/kg, the current National Research Council recommendation for dietary vitamin E in horses. These data, though limited, should provide excellent guidelines for use in formulating appropriate levels of vitamin E supplementation for zoo rhinoceros. Based on field observations, diets fed to black rhino should contain a minimum of 150 IU, and more likely 250 IU vitamin E per kg of dry matter. Future projects will be designed to investigate seasonal and other environmental as well as physical (i.e. fire, grazing pressure) influences on vitamin E in plants, in an effort to refine not only herbivore feeding recommendations, but also plant conservation in relevant locations.
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Vitamin E levels measured in rhino browse plants
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