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Dierenfeld, E.S.; Waweru, F.K.; Du Toit, R.; Brett, R.A., 1990. Alpha -Tocopherol levels in plants consumed by black rhinoceros (Diceros bicornis): native browses compared with common zoo forages. Proceedings of the American Association of Zoo Veterinarians 1990: 219-221, 2 tables

Location: World
Subject: Physiology
Species: All Rhino Species

Original text on this topic:
Plasma -tocopherol levels in free-ranging black rhinoceros (Diceros bicornis) have previously been shown to be higher than in zoo animals (0.8 vs.0.2 g/ml, P< 0.001). Dietary vitamin E levels may be correlated with health problems observed in captivity. Plants (n=73) consumed by black rhinos were collected from the Zambezi Valley in Zimbabwe, and 4 locations in Kenya.
Following tissue homogenization, lipids were extracted from fresh plants using sodium dodecylsulfate, ethanol, and hexane. Aliquots were evaporated under N2, reconstituted with methanol containing BHT, and kept under freezer storage until analysis via HPLC. Sample preparation was rapid and convenient; results were highly repeatable under field laboratory conditions. Leaf stem ratios and dry matter determinations were conducted separately on duplicate samples. Similar sample preparation was applied to green produce, selected browse plants, and dried forages fed at the New York Zoological Park. Results of these assays are presented in Table 1 (selected African plants) and Table 2 (locally available feeds).
Leaves contained 2 - 50 times more -tocopherol than stem fractions of the same plant; mature tissues had higher concentrations than young, growing parts. Of native browses, whole plants ranged from 4.1 (Acacia drepanolobium) to 420.9 (Scutia myrtinus) mg -tocopherol/kg dry matter. Dark green, leafy produce fed at the zoo (n= 7 spp.) contained an average of 157.0 mg -tocopherol/kg dry matter; fresh browses or grass (n= 9 spp.) ranged from 25-203 mg/kg dry matter (x= 72.5); dried forages averaged 22.3 mg/kg dry matter. NRC dietary vitamin E recommendations for horses (1989), used in designing diets for zoo rhinoceros, are currently 50 to 80 mg/kg. Almost half (43%) of the native browses sampled in this study contained higher levels than current NRC recommendations; dried forages were consistently < 50 mg/kg, and fresh green plants were highly variable. These data suggest that typical zoo diets (hay, grain, and some fresh browse or green produce) fed to zoo rhinoceros may provide marginal vitamin E nutrition.
Table I. Mean (? SE) -tocopherol content of leaves and stems from important browse species consumed by the black rhinoceros in Kenya (n= 5 spp. from 3 different sampling locations) or Zimbabwe (n = 10 spp.). All data are presented on a dry basis.
Species Leaf:Stem -tocopherol mg/kg
Ratio leaf stem
Kenyan Plants:
Acacia xanthophidea 28:72 64.8 ? 19.9 15.7 ? 6.2
Carissa edulis 56:44 86.4 ? 17.9 29.2 ? 13.7
Enthrococcus bongensis 32:68 207.4 ? 81.3 23.8 ? 6.4
Grewia similis 54:46 96.3 ? 45.7 21.6 ? 7.3
Rhus natalensis 65:35 183.1 ? 99.8 23.3 ? 9.9
Zimbabwean Plants:
Balienia spp. 31:69 178.9 4.9
Colophospennum mopane 66:34 135.6 133
Combretum eleganoides 52:48 83.3 6.1
Combretum mossambiencis 45:55 289.3 26.6
Diplorhyncus spp. 57:43 72.0 12.0
Grewia bicotor 55:45 341.6 7.3
Grewia flavescens 15:85 63.0 19.4
Holinskioldia spp. 18:82 100.2 2.7
Markhamia acuminata 46:54 96.1 13.5
Securinegra virosa 17:83 57.5 4.8
Table2. -tocopherol content of selected green forages, green produce, and dried forages fed at the New York Zoological Park.
Green Forage -tocopherol
(or browse) (mg/kg dry matter)
Alder 47.9
Bamboo 202.5
Clover 33.3
Duck-weed 33.2
Grape 66.3
Grass 71.4
Maple 25.4
Mulberry 127.1
Willow 45.5
Dried forages
Ifalfa Cubes 5.9
Mixed hay (Alfalfa:Timothy) 26.8
Timothy hay 34.1
Green produce
Bok Choi 206.1
Broccoli (florets) 44.2
Collard Greens 160-5
Dandelion Greens 129..4
Hydroponic Grass 71.4
Kale (leaves) 136.1
Kale (stems) 24.4
Mustard Greens 158.5
Romaine 163.9
Spinach 143.4

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