Rhino horn is prized in Asia for use in traditional remedies and surging demand has meant more poaching. A record 1305 of the animals were illegally killed in Africa last year. Buying and selling rhino horn internationally was banned in 1977.
But opponents of that ban say that, as rhinoceros' horns grow back if cut from a living animal, a properly monitored legal trade could help save the rhinos, rather than condemn them to extinction.
The stakes are high. The government has not revealed the size of its rhino horn stockpile - those seized from from smugglers as well as ones cut from animals that died naturally - but the Private Rhino Owners Association estimates its members have around 6 tonnes and reckons the state has close to 25 tonnes.
Rhino horn on the street in Asia sells for around $US65,000 ($NZ95,000) per kg, according to off-the-record estimates by conservationists, so 30 tonnes could generate up to around $US2 billion ($NZ2.9 billion).
Supporters of legalising the trade say the money could be used for conservation by the South African government, whose finances are under mounting pressure as it faces possible debt ratings downgrades that could see its borrowing costs balloon.
They also say the ban simply does not work.
"We are losing rhino, we are losing the war. We have to change our tactics," said John Hume, a private rancher who owns 1,293 rhinos - 4.5% of a global population of around 28,000 in Africa and Asia.
"It is not the demand that is killing our rhinos, it's the way we supply that demand," he said on his sprawling 7000ha ranch 170km west of Johannesburg.
Small groups of rhino cluster under thorn trees along the ranch's dirt roads. Some hulking brutes weigh over two tonnes, an intimidating presence which would be all the more so if they still had horns.
Hume dehorns his animals, which makes them less enticing to poachers and adds to his stockpile than now amounts to five tonnes. Dehorning is done while the animal is sedated and does not hurt as the material is similar to human fingernails.
Private ranching of wild animals is legal in South Africa, where about 6,200 rhinos are in private hands, a third of the national population.
HORNS OF A POACHING AND TRADE DILEMMA
If South Africa does decide to submit a proposal to lift the ban, it will face stiff resistance. Animal welfare organisations say a legal trade could encourage more poaching by criminal gangs seeking to launder "dirty" horns in clean markets.
"Legalizing rhino horn trade would remove the stigma associated with consumption of endangered species, stimulate the insatiable demand for rhino horn, and fuel further rhino poaching," the International Fund for Animal Welfare said on its website.
A 2013 IFAW-commissioned study concluded a legal trade would be fraught with uncertainty and that illicit dealers could respond by reducing prices to retain their market share.
The South African cabinet will decide this month whether to table a proposal on lifting the ban when the Convention on International Trade in Endangered Species (CITES) meets in Johannesburg in September-October this year.
Having the international ban overturned would require two-thirds support from the countries attending.
One tool to prevent illicit horn from coming to the market is forensics. For both rhino horn and elephant ivory, science can pinpoint when an animal was taken and in many cases where.
"They are doing a good job in South Africa of developing a comprehensive data base. It determines where the rhino horn has been sourced," CITES Secretary General John Scanlon said.
Scanlon said forensics could discourage speculators who hope to poach rhino now and then offload the horn if the global ban is lifted.
Trading rhino horn within South Africa's borders is legal, after a high court late last year struck down a moratorium imposed in 2009. A permit is required for such transactions but no one has applied for one yet.
The moratorium was briefly put back in place as the Department of Environmental Affairs filed to oppose its lifting but in January this was set aside.
"As from 20 January 2016, the High Court's order setting aside the domestic moratorium on the trade in rhino horn is once more effective," said Roopa Singh, spokeswoman at the Department of Environmental Affairs.
For Hume, a blunt-talking businessman who made money in the resort and hotel industries, the issue is clear. "The fact that we can't sell a renewable, sustainable product is absolute madness."
