A "lure animal" is an animal, often a dog but can also be rabbits, possums, raccoons, etc. that is released into an enclosure with a dog bred and trained for fighting. These animals are often muzzled so that they can't do any serious damage to the fighting dog, and they are typically left in the enclosure until the fighting dog kills the lure animal; rarely are they reused. As far as I'm aware, this practice (and dogfighting) is banned in all fifty American states, Puerto Rico, and a majority of European countries, though in some parts of the world dogfighting is still considered a sport.
Fighting dogs are often also made to run tens of miles on treadmills, and bound to deliberately-heavy chains to build muscle and endurance. I came across a video documentary on the topic, and I found it to be thoroughly educational and entertaining. It's easy to understand why it's illegal in so many places, but it's really quite interesting how people came up with all these different techniques to prepare the dog for the ring. I came across these nuggets of information while researching dogfighting for my Nanowrimo project.