XI'AN, Feb. 28 -- Rare brown panda Qi Zai has faced temperatures of minus 30 degrees Celsius in the remote Qinling Mountains of west China this winter, but has come through unscathed, according to staff with a "training base" toughening him up for release into the wild.

The six-year-old male is the world's only completely brown panda, found among a colony of pandas with some brown in their coats.

He has been kept in the Wild Panda Training Base in Shaanxi Province's Foping Nature Reserve for two years. Staff initially fed Qi Zai artificially, but have left him to fend for himself this winter.

The Qinling giant panda is a subspecies of giant panda that was recognized in 2005. It has a smaller and rounder skull, shorter snout and less fur than the more familiar Sichuan subspecies.

The world's first brown panda was discovered in 1985 in the Qinling Mountains. Since then, there have been eight brown pandas found, but Qi Zai is the last remaining alive.

Weighing about 105 kg, Qi Zai was energetic and ate 50 kg of bamboo a day during the winter, according to his keepers.

They are preparing to allow him to mate with a black panda when he is more sexually mature, which may help to figure out the genetic mystery behind his brown fur.