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Black Rhino Horns Contained More Selenium and Molybdenum Than White Rhino Horns

Male white rhinoceros in the Kalahari Desert of Namibia
Research · Molecular biology & biochemistry

Trace-element concentrations in rhinoceros horn differed among species in an analysis of 82 horns. Rhino horn is made of keratin, but it grows from living, vascularised tissue at its base, allowing small amounts of elements from the body to become incorporated as the horn forms. Black rhinoceros (Diceros bicornis) horn contained clearly higher selenium and molybdenum concentrations than white rhinoceros (Ceratotherium simum) horn. Copper tended to be higher in white rhino horn, but the analysis provided only weak support for that difference.

The final dataset included 41 black rhinos, 29 white rhinos, nine greater one-horned rhinos (Rhinoceros unicornis), one Sumatran rhino (Dicerorhinus sumatrensis) and two horns whose species could not be determined. Fourteen trace elements were tested, although three were below measurable levels in the horn samples.

Species mattered more than sex

The analysis did not support a clear difference in horn concentrations between males and females. Species differences were clearer: selenium and molybdenum were higher in black than white rhino horn, and cobalt was higher in black than greater one-horned rhino horn.

The authors interpret these differences as evidence that horn chemistry partly reflects biological and environmental differences among rhino populations rather than simply external contamination of the horn surface.

The Africa–USA comparison was preliminary

A geographic comparison used seven horns from wild African rhinos and 52 horns from rhinos managed in the United States. Arsenic and barium were higher in the African group, while copper and zinc were higher in the U.S. group. The source countries of the African horns were not specified.

The authors stress that this comparison is preliminary because the African sample was small and the origin of several other horns in the wider dataset was unknown. The result therefore does not establish a general continental pattern for rhinoceroses.

Horn chemistry was a poor individual diagnostic for most elements

Matched horn and liver material was available from 21 rhinos. For arsenic across species, animals with higher horn concentrations also tended to have higher liver concentrations; selenium showed the same pattern within black rhinos. For most other elements, horn concentrations did not clearly track the matched liver concentrations of the same individual.

The authors therefore suggest that horn keratin may be useful for studying trace-element patterns at population level, but is generally not a direct diagnostic substitute for internal tissue measurements in individual rhinos.

Sources and image credit

  1. Roth, T. L., Rebolloso, S. L., Donelan, E. M., Rispoli, L. A., Freeman, E. W., & Buchweitz, J. P. (2026). Horn trace element profiles of managed rhinoceros species and comparisons to matched livers and wild African rhinoceros horns. PLOS ONE, 21(7), e0353566. https://doi.org/10.1371/journal.pone.0353566Primary peer-reviewed open-access research article published 9 July 2026. Eighty-two horn samples from four rhinoceros species were analysed for 14 trace elements, with 21 matched liver samples used to test horn–tissue relationships. The authors describe the Africa–U.S. comparison as preliminary because only seven African horns were available.

Image: Giles Laurent / Wikimedia Commons — live male white rhinoceros in the Kalahari Desert of Namibia; representative species image, not a study animal · CC BY-SA 4.0 · Source

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Molecular biology & biochemistry

SPECIES IN THIS STORY

Species in this story

Black Rhinoceros Diceros bicornis Explore species White Rhinoceros Ceratotherium simum Explore species

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