The Chechen's Rottweilers were a pack of vicious attack-dogs, owned by The Chechen.
A Rottweiler attacked Batman, resulting in a hideous scar and more protective gear.
Towards the end, the Joker had The Chechen taken away, threatening to have his men cut up into pieces and fed to his dogs to see how "loyal" they are.
In their final battle at the Prewitt Building, the Joker used the dogs to attack Batman, injuring him further and allowing Joker to gain the upper hand. However, Batman managed to knock them off a ledge and killing the Rottweilers instantly.