A novel twist on the controversial practice of injecting poison into the horns of living rhinos has been suggested by an Indian doctor: the addition of gossypol, a natural phenol derived from the cotton plant, which causes azoospermia in humans, essentially rendering men infertile.

Dr Nishit Sawal, a neurologist at the All India Medical Sciences institute in Delhi, believes spiking horns with gossypol will make Vietnamese and Chinese consumers of horn think twice before using it. ‘A single dose of gossypol can cause azoospermia in humans, lasting two to three years and which is permanent in some,’ he says.

White rhino

Gossypol is itself a yellow pigment, but Dr Sawal says if it does not cause any perceptible colour change in the horn, tartrazine yellow pigment could also be injected ‘so poachers see it and realize that shooting the animal and taking the horn will be futile.’

Gossypol has been used in the past by the Chinese government as a male contraceptive, but was abandoned because of side-effects such as low blood potassium levels, digestive problems, and persisting low fertility levels after treatment was stopped.

A number of reserves in South Africa have been injecting toxic substances such as parasiticides into the horns of their rhinos in an effort to put off poachers. These substances generally cause illness such as nausea, diarrhoea and stomach ache, but are non-lethal.

Rhino horn is used for a number of medicinal purposes in southeast Asia, including fever suppression (there is some evidence that it may have a mild effect, albeit less than aspirin), curing hangovers (no known evidence of efficacy, but probably used more as a status symbol of wealth), and reportedly as a cancer treatment (again, no known evidence of efficacy). Contrary to popular belief in the west, it does not appear to be used as a form of natural Viagra or aphrodisiac.

Critics of poisoning horn argue that poachers and traffickers motivated by greed and profit will not care if some consumers suffer ill effects, and will bleach horns to remove traces of any dye.