Lions can't be tamedOne interesting study found that lions are entirely unsuitable to life in captivity (Clubb & Mason, 2003, 2007). In the wild, lions have one of the largest home ranges of all large carnivores, in which they travel in on a daily basis.
As part of the zoo's safety policy, zookeepers are never in the same enclosure with a carnivore unless the animal is sedated and that can make check-ups a little difficult.