White rhinoceros Ceratotherium simum horn development and structure: a deceptive optical illusion

Abstract

The alleged traditional medicinal properties of rhinoceros horn resulted in a dramatic escalation in rhinoceros poaching in South Africa. Despite the listing of all species of rhinoceros in the International Union for Conservation of Nature Red List of threatened animals, their numbers are still declining rapidly. Based on the assumption that rhinoceros' horn consists of a collection of hollow tubules and intertubular hollow spaces, which allow internal fluid distribution, a horn devaluation procedure through infusion of chemicals and dyes was recently introduced. This procedure is costly and has a mortality risk. This study provides the first detailed description of the development and resultant structure of the rhinoceros horn. The unique solid structure which consists of a large number of tightly packed filaments is the result of the cellular orientation of squamous epithelium corneocytes.What was previously thought to be microtubules is an optical illusion created by the orientation of the corneocytes in the solid filaments. We contest the scientific basis for infusing chemicals into the rhinoceros horn as a deterrent for human use.

No evidence that horn trimming affects white rhinoceros horn use during comfort behaviour and resource access

“…Rhinos also dig with their horns during wallowing behaviours (Wilson et al, 2020) which act to protect the skin from parasites and aid in thermoregulation on hot days (Metrione & Eyres, 2014). However, unlike the horns of several tropical bovid species (Picard et al, 1999), rhino horns have no thermoregulatory function as they are made of keratin and lack a vascularised bony core (Boy et al, 2015). Prior to wallowing, Sumatran rhinos dig soil from the banks of pits with their horns and feet, a practise that likely acts to thicken the consistency of the mud (Van Strien, 1985).…”

Microstructure and mechanical properties of different keratinous horns

“…Prior studies [22,23] showed that tubular and lamellar structures exist in the bighorn sheep horn. Flattened and cornified epithelial cells (keratinized cells) grow from dermal papilla that are arranged in concentric layers around a central medulla, forming the tubular structures [24][25][26]. Tubular structures in other keratinized tissues such as equine hooves and rhinoceros horns were identified and characterized in previous studies [24,27,28].…”

Risky conclusions regarding shrinking rhino horns

“…A rhino's horns grow continuously from a growth layer at the base of the horn (Boy et al, 2015). Although African black and white rhinos have similar intrinsic horn growth rates, irrespective of sex, the rate varies with age (Pienaar et al, 1991).…”