@Sun Wukong, you are right, that lot of animals are closely releated in european zoos, such onagers, mesopotamian fallow deers, gaurs, bush pigs etc., but in american zoos has been established a population of mountain tapirs for years, it would been a risk to import such rare animal for a long distance, Stuttgart zoo have tryied to import a male from L.A. years ago, but the animal have died during the transport.
In addition, it is an expensive thing to import the animals, Cologne zoo search for momeny this time, to built new enclouser for hippos and crocodilles, so I am not supposed they get a mountain tapir in nearly future, in addition, they have built a new tapir enclouser recently and keep a young pair lowland tapirs with hope to breed.