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Iron overload disorder (IOD) can lead to organ dysfunction and may exacerbate other diseases in the critically endangered black rhinoceros ( Diceros bicornis). It is important to develop methods for monitoring the progression of iron storage (hemosiderosis), diagnosing the disease, and evaluating treatments in this species. Traditionally, an equine enzyme immunoassay (EIA) was used to measure rhinoceros ferritin, a serum protein correlated to iron stores. The goal of this study was to validate a rhinoceros-specific assay and investigate factors potentially associated with ferritin concentrations in black rhinoceros. A ferritin EIA developed for Sumatran rhinoceros was validated for black rhinoceros via Western blot analysis of liver ferritin and confirmed parallelism of serum samples to the EIA standard curve and used to analyze serum samples ( n = 943) collected from 36 black rhinoceros (<1-33 yr) at 14 U.S. institutions. Mean (±SEM) serum ferritin concentration was 6,738 ± 518 ng/ml (range: 85-168,451 ng/ml). Concentrations differed among individuals with eastern black rhinoceros (7,444 ± 1,130 ng/ml) having a higher mean ferritin than southern black rhinoceros (6,317 ± 505 ng/ml; P < 0.05) and higher mean values in wild-born (11,110 ± 1,111 ng/ml) than captive-born individuals (3,487 ± 293 ng/ml; P < 0.05). Ferritin concentrations did not differ between young rhinoceros (<5 yr old; 2,163 ± 254 ng/ml) and adults (7,623 ± 610 ng/ml) and were not correlated with age ( r = 0.143) or time in captivity ( r = 0.146, wild born; r = 0.104, all animals). Ferritin concentration was not impacted by sex (female: 2,086 ± 190 ng/ml; male: 8,684 ± 717 ng/ml), date, month, or season of collection ( P > 0.05). Data indicate ferritin concentrations are variable and not necessarily associated with IOD; ferritin is not recommended for diagnosing or monitoring IOD in black rhinoceros.

The African black rhinoceros (Diceros bicornis) has adapted to a low iron diet during evolution and is thus prone to iron overload in captivity, which is associated with a number of serious disorders. A S88T polymorphism in the HFE gene has been suggested as a potential genetic basis of increased iron uptake in the black rhinoceros, while the Indian rhinoceros is thought to be unaffected by iron overload in captivity. In the present study, the histopathology and distribution of iron accumulations in five black rhinoceroses with iron overload syndrome were characterized and compared with three Indian rhinoceroses (Rhinoceros unicornis) and one African white rhinoceros (Ceratotherium simum). At necropsy examination, iron storage in black rhinoceroses was not associated with gross lesions. Microscopically, the most consistent and highest degree of iron load was found in the spleen, liver, small intestine and lung. There was minimal fibrosis and single cell necrosis in the liver. Endocrine organs, lymph nodes, heart and kidney were less often and less markedly affected. Unexpectedly, Indian rhinoceroses also showed iron load in the spleen and smaller amounts in organs similar to the black rhinoceros except for in the heart, while the white rhinoceros had only minor detectable iron storage in intestine, liver and lung. Sequence analysis confirmed the HFE S88T polymorphism in black but not in Indian rhinoceroses. The results indicate that Indian rhinoceroses may also be affected by iron storage in captivity, although in a milder form than the black rhinoceros, and therefore challenge the relevance of the S88T polymorphism in the HFE gene of black rhinoceroses as the underlying cause for iron overload., (Copyright © 2012 Elsevier Ltd. All rights reserved.)