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| Location: |
World |
| Subject: |
Physiology |
| Species: |
All Rhino Species |
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Previous work from our laboratory and others has documented differences in plasma alpha-tocopherol levels between zoo (0.2 micrograms/ml) and free-anging (0.8 micrograms/ml) black rhinos, and suggested that many captive animals may be suffering from vitamin E deficiency. This original comparison was conducted on blood samples (n =31) taken during a translocation operation in Zimbabwe in 1988. Subsequent to that study, we quantified plasma alpha-tocopherol from 44 free-ranging black rhinos sampled in South Africa, 7 in Kenya, 4 in Namibia, and an additional 24 animals in Zimbabwe. These latter results averaged 0.6, 0.2, 0.8 and 0.5 micrograms/ml, respectively.
Because plasma and dietary levels of alpha-tocopherol (as a measure of vitamin E activity) are closely correlated, the differences seen among these various rhino populadions suggested widely varying diets and/or habitat quality. To investigate this possibility, a collaborative field study with F. Kamunde Waweru, Wildlife Conservation International, Kenya, R. duToit, Zambezi Rhino Project, and R. Brett, World Wildife Fund, Kenya, was organized to quantity alpha-tocopherol levels in major browse species consumed by black rhinos. Four locations in Kenya (2 national parks, 2 private reserves) 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 fullsized tank of nitrogen gas, were loaded into vehicles and driven to makeshift labs. Converted storerooms or kitchens generally met our relatively minor requirements of counter space, an ectrical source, and water, although we were treated to a true .tb space 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 States for analysis via high-performance liquid chromatography.
African collaborators, all experienced field researchers, identified major food plants (a minimum of 10 species per site) for sampling. Results indicated wide variation in vitamin E levels in fresh rhino browse plants. Leaves contained 2- to 50-fold 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 quantified for this preliminary study. Rainfall, temperature and sunlight effects on alphatocopherol 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/ kg dry matter [equivalent to 6-630 International Unfts of Vitamin 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 quantified from animals in the various
sites. For example, the Zambezi Valley plants (n=27) averaged 45.5 mg/kg alpha-tocopherol (range 6.4 to 191.8) whereas the Kenyan location from which animals with the lowest plasma alpha-tocopherol had been bled 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 > 50 IU/kg, the current National Research Council recommendation for dietary vitamin E in horses. These data, although limited, should provide excellent guidelines for use in formulating appropriate levels of vitamin E supplementation for zoo rhinoceros. Based on these field observations, diets fed to black rhinos should contain a minimum of 150 IU, and more likely 250 IU vitamin E/kg 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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