Armed with a dart gun in a helicopter hovering above Somkhanda game reserve in South Africa, the vet Dr Mike Toft has just shot a powerful cocktail of drugs into the massive white rhino below.

The 2,000kg (315st) bull starts to stagger and sinks slowly to its knees as the drugs take effect. Though immobilised, the rhino is conscious. So, once it has been moved into the right position by a team on the ground, foam earmuffs and a blindfold are placed on its head to reduce stress levels.

After marking the ideal cutting point to avoid damaging the living growth plates at the base of the horns, Toft fires up a chainsaw and slices both of them off.

Those magnificent horns, which have helped to protect this species for millions of years, are the reason that more than 7,000 rhinos have been killed in South Africa in the past decade. A persistent human desire for rhino horn – for everything from traditional medicine to hangover cures or status symbols – drives the slaughter of more than 1,000 of the animals each year in the country that has the largest rhino population in the world.

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Worldwide, the situation is grave. The northern white rhino became functionally extinct after the death of Sudan, the last male, in March, while the black rhino population is down to about 5,200. The situation for Asian rhinos is equally bleak: there are just 3,200 surviving Indian rhinos, about 76 Sumatran rhinos and 60 Javan rhinos. There are fewer than 30,000 rhinos globally, with Africa’s southern white rhino the most populous species at about 20,000.

These alarming figures have driven wildlife managers in several South African reserves to take the drastic step of sawing off hundreds of horns every year, before criminal syndicates can get their hands on them. With the poachers’ prize removed, the risk to the hornless animals is greatly reduced.

Facebook Twitter Pinterest Horns at the ranch of the rhino breeder John Hume, who believes the only way to ensure the survival of the species is by farming the animals and legalising the sale of rhino horn globally. Photograph: Leon Neal/Getty Images

The strategy has produced dramatic results in several reserves. Chris Galliers, chairman of the Game Rangers Association of Africa, analysed 2010-15 poaching statistics from the south-eastern province of KwaZulu-Natal and found that nearly a quarter of rhino deaths were on private reserves. But over the past two and half years, coinciding with the intensive dehorning efforts, that has dropped to 5%.

Toft has removed close to 1,800 horns from 900 rhinos in the past three years in KwaZulu-Natal, which has been heavily targeted by poachers. Both Galliers and Toft acknowledge that dehorning is not a permanent or ideal solution to the crisis. “This is not something we want to do. It’s expensive and invasive but we believe it is a necessary evil,” says Galliers, noting that it costs about £580 to safely dehorn a rhino.

Horn trimming rhinos in South Africa – in pictures Read more

The cost is based on the hiring of helicopters and skilled vets. Galliers, also head of the anti-poaching initiative Project Rhino, points out that dehorning must be repeated every 18-24 months as the horns regrow naturally.

Even then, there have been cases of dehorned animals being shot for their stumps. Toft has developed a method of removing as much horn as possible without causing pain to the rhino or damage to its growth plates. The horn is removed to about three finger widths from the base, then the stump is further trimmed around the edges with an angle grinder, enabling the removal of an extra 2kg of horn on a large bull.

The operation is noisy and violent, but there is no blood – and Toft insists it is no more painful than trimming your fingernails if done correctly.

Facebook Twitter Pinterest A dehorned rhino at a farm outside Klerksdorp, South Africa. Photograph: Siphiwe Sibeko/Reuters

Galliers and Toft believe dehorning could help save rhinos under threat elsewhere in Africa and Asia. But the cost means that might only be possible in small and medium-sized reserves.

Dehorning only selected bulls is not an option, as those without horns would be more vulnerable in territory fights. In parks where the entire rhino population is dehorned, all bulls are placed at equal disadvantage. But dehorned rhinos can still fend off lions by using their considerable bulk as a weapon, Toft says.

For trophy hunters, the aim is to acquire both the head and the horns. Many other horned animals are hunted: elephants are slaughtered for their ivory, but Toft does not think detusking is a solution. Tusks are partially hollow and contain sensitive roots and nerves. Although it would be feasible to remove the solid portion, a large volume of tusk would have to remain intact, which could still attract the attention of poachers. Tusks are also essential tools for elephants to strip tree bark or dig up succulent roots and tubers.

For now, dehorning appears to be achieving success as an emergency measure, buying time while the decades-old debate continues about how to end the demand for rhino horn.

This article is part of a series on possible solutions to some of the world’s most stubborn problems. What else should we cover? Email us at theupside@theguardian.com