In ZOO With Predators, Argentina

The downside to breeding the animals in captivity is that thousands of them are placed on "surplus lists" each year, and sold to circuses, animal merchants, auctions, pet owners, and game farms. The San Jose Mercury News conducted a two-year study that suggested of the 19,361 mammals that left accredited zoos in the U.S. between 1992 and 1998, 7,420 (38 percent) went to dealers, auctions, hunting ranches, unaccredited zoos and individuals, and game farms.
Zoos have advertised surplus animals in the Animal Finders' Guide, a newsletter in which the owners of hunting ranches post notices of sales and auctions. Matthew Scully writes that many hunters prefer killing animals from zoos because they make better-looking trophies; the mane of a zoo lion will tend to be cleaner than that of a wild lion. In one case, a zoo owner named William Hampton was found to have been buying animals and systematically slaughtering them in order to sell their skins, heads, and pelts as trophies.
Animals that breed frequently, such as deer, tigers, and lions may be killed for their meat; Nuremberg zoo's deputy director, Helmut Mägdefrau, has said, "If we cannot find good homes for the animals, we kill them and use them as feed." Other animals may be sold to smaller zoos with poor conditions. PETA cites the case of Edith, a chimpanzee found in a concrete pit in a roadside zoo called the Amarillo Wildlife Refuge in Texas. She had been born in the Saint Louis Zoo, but had been sold just after her third birthday, and for the next 37 years was passed around five other facilities before landing in the roadside zoo.
It was alleged in March 2008 that hundreds of the Berlin Zoo's 23,000 animals are missing, amid allegations that they have been slaughtered, and that some tigers and leopards were sent to China to make drugs for traditional Chinese medicine. Claudia Hämmerling, a Green Party politician, said she had evidence that four Asian black bears and a hippopotamus were taken from Berlin to go to a new home, but were transported instead to Wortel in Belgium, which The Guardian reports has no zoo, but does have a slaughterhouse. The zoo's director, Bernhard Blaszkiewitz, replied that the allegations were "untruths, half-truths and lies."