Rhinoceroses are already one of the most threatened animals on the planet because their horns can rack up a fortune in the black market. Now, after poachers stormed a zoo in France and slaughtered Vince, a 4-year-old captive-born rhino, for his horn earlier this month, even zookeepers are taking new measures to protect their rhinos from killers.

Eighteen black and white rhinos at the Dvur Kralove zoo in the Czech Republic are about to be sedated so that their horns can be removed β€” in hopes it will save their lives should attackers come along.

"It's for the sake of rhino safety," Andrea Jirousova, a spokeswoman for the Dvur Kralove zoo, told The Guardian. "The attack [in France] put us on the alert β€” the danger is really intense."

Worth more than its weight in gold, rhinoceros horn is made of keratin, a material each one of us grows right on the tips of our fingers. But the keratin from a rhino horn is illegally trafficked by organized crime groups across borders because of the unfounded superstition in that it cures everything from hangovers to cancer.

"This is poaching on a whole new level," Azzedine Downes, president and CEO of the International Fund for Animal Welfare (IFAW), told The Dodo at the time of Vince's death. "Wild rhinos have been in the sights of poachers for many years. It's horrifying to imagine a captive rhino falling prey to poachers' bullets."

The attack on Vince came less than two weeks after poachers broke into a rhino orphanage in South Africa and killed two baby rhinos, each just 18 months old, for their tiny horns.

Some game reserves in Africa have also taken a chainsaw to their rhinos' horns in order to save their lives, because poaching has become such a dire crisis. In 2016, an estimated 1,100 rhinos were killed in South Africa, which is home to about 70 percent of the world's rhino population. The year before was even worse: 1,175 rhinos in South Africa were killed for their horns β€” an average of three slaughtered rhinos per day. And it's estimated only about 29,500 rhinos are left in the world.

"Any and all methods, including dehorning, should be supported as a deterrents to save the lives of the rhinos," Paul Oxton, founder and director of Wild Heart Wildlife Foundation, told The Dodo.

Oxton said that in the long-term there need to be educational campaigns in countries where there's high demand for rhino horn, to ultimately save lives.

There are also three calves at the Czech zoo who will not undergo the surgery for now. Because rhino horns grow back, the rhinos at the zoo may have to have more procedures in the future.

To help rhino orphans left behind by poaching attacks, you can make a donation to Thula Thula Rhino Orphanage.