I think it is unacceptable from the welfare point view for the pray (poor animal), and in some cases for the predator itself (because the pray can injure the predator). It is also unacceptable because some of the public is sensitive watching the scene. It can also be unacceptable due to a veterinary disease reason, because a live pray can transmit a disease or a parasite to the zoo animal. One example would be a live pig that can transmit the pseudorabies virus (suid herpesvirus-1, SHV-1) which can be fatal for carnivores like felines and it is not for the pigs. All animals can be considered as carriers of some herpesviruses, that can be very virulent in unusuall hosts like an animal from a different species. In the case, the donkey may harbor an equine herpesvirus. Another example is the herpesvirus simiae (herpesvirus B) from the Asian macaques (particularly pig-tailed, crab-eating and rhesus), which is not fatal for the macaques (its natural hosts), but it is fatal for humans (causing fatal encephalitis in most of the cases).