A rhino died at a South African park after having an anti-poaching tracking device placed inside its horn, the owner of a private reserve said Thursday. Spencer the rhinoceros had been sedated so that a microchip could be placed in his horn, but he died when veterinarians at the Rhino and Lion Nature Reserve injected him with drugs to wake him up. The animal was suspected to have had an underlying condition that triggered heart failure, the Sapa news agency reported. \"He responded very well to the treatment and the procedure is 100 percent safe, but there are always huge risks when such a large animal is sedated,\" said Lorinda Hern, the owner of the 22-year-old rhino. Implanted tracking devices are one of the anti-poaching methods being tested in South Africa, where about 450 rhino were killed for their horns last year -- up from 13 in 2007. The largest horns can fetch up to half a million dollars and feed the Asian traditional medicine market, despite scientific evidence that they have no medicinal value.