If you're wondering what exactly Michael Vick was up to with all that dogfighting business, you might be interested in Harry Crews' 1976 Southern gothic novel A Feast of Snakes, which features a character who is deep into the depraved world of dogfighting. Among other things, Big Joe Mackey leashes his dogs to a treadmill and turns up the speed until they just can't take it no more. It's twisted stuff, though highly believable, and no less cruel than what Vick is accused of doing.
A Feast of Snakes is not the best animal-fighting novel I have read, though. That honor would go to 1962's Cockfighter by Charles Willeford, the author of Miami Blues and the other Hoke Moseley novels. If you didn't know he was a real novelist, you would think that Cockfighter had been written by someone who had spent his entire life in the world of cockfighting and was trying to get it all down on paper. There's a real ascetic quality to the book: It's wall-to-wall cockfighting, and there's nothing in there that isn't cockfighting. Highly recommended.