Training can relieve stress by providing opportunities for animals to participate in their own care. For years, animal keepers have used training techniques to encourage animals to shift from one holding cage to another. The easiest way for some keepers to induce this behavior was with negative reinforcement. Often this was in the form of a hose, net, trash can lid, etc. The animal learned to move to another area to avoid the negativity and reduce the stress.
Negative reinforcement is a valid way to influences behavior.
Animal behavior in the wild is frequently shaped and influenced by negative reinforcement. A primate will move out of the dominant animal's area to avoid confrontation. However, as a training tool, negative reinforcement has its limits. A general rule of negative reinforcement is that an animal trained with negative reinforcement will only work at the level necessary to avoid the negative stimulus. For example, an elephant will only lift it's leg high enough to avoid the bull hook.