Johannesburg - Several hundred rhino horns will go under the hammer on Wednesday in South Africa's first online auction of the controversial product, despite opposition from conservation groups who contend the sale will encourage poachers.The three-day sell off, organised by the owner of the world's largest rhino farm, will go ahead after a last-minute legal tussle pushed its start back two days."There are delays, no hiccups. It starts tomorrow [Wednesday] at two o'clock," said auction organiser John Hume, who owns 1 500 rhinos on his farm north of Johannesburg.Hume has stockpiled six tonnes of rhino horns and wants to sell 264 pieces weighing a total of 500kg.He says he harvests the horns by tranquilising the animals and dehorning them - a technique he says is humane and wards off poachers.Read: Wildlife Act responds to John Hume ahead of delayed rhino horn auctionActivists opposed to the sale fear it will fuel trafficking and undermine a 40-year global ban on the rhino trade.Animal protection charity Humane Society has opened an online petition urging the government not to issue permits to potential horn buyers."Any domestic trade in rhino horn undermines enforcement and demand reduction efforts to battle wildlife trafficking in the rest of Africa, China [and] Vietnam," the charity said.The divisive sale comes after a court decision to lift an eight-year moratorium on the domestic trade of rhino horns in April.A last-minute legal challenge delayed the auction for two days, but Hume was given a permit on Monday and bidding is set to begin. Also read: Online rhino horn auction goes to courtEnvironment Minister Edna Molewa said the government was taking steps "to ensure that we have closed any possible loopholes that could pave the way for a circumvention of [international] regulations".Speaking on Monday, the minister said an audit of all existing rhino horn stockpiles was underway to "prevent the smuggling of illegally-obtained horns out of the country".No 'blood horns' Private rhino owners say so-called "blood horns" will not enter the market, as each horn is micro-chipped and their origins can be DNA-traced.Breeders believe open trade is the only way to stop poachers from slaughtering the endangered animals.They argue that the auction helps to promote "sustainable" use of resources and raise funds for protecting and conserving the rhino.South Africa is home to around 20 000 rhinos, or about 80% of the worldwide population, but in recent years the country has suffered record slaughter by poachers.Rhino horns are highly prized in Asia, where they are estimated to fetch up to $60 000 a kilo on the black market, exceeding the price of gold or cocaine.They consist mainly of keratin, the same component as in human nails, and are sold in powdered form as a supposed cure for cancer and other diseases - as well as a purported aphrodisiac - in Vietnam and China.Van's Auctioneers, who will conduct the auction, have not set an opening price for bids, but bidders need to pay R100 000 to register.Pelham Jones, chairperson of the Private Rhino Owners Association, told AFP that potential buyers would be people of Asian descent who live in South Africa and "could potentially be consumers of the product".Commodity speculators based anywhere in the world will also be able to buy, "but may not export the horns", he added.Any registered buyer will be able to bid, but may not collect the horns until they obtain permits.