This might sound retarded but did he get a longer sentence because it was a cop-horse? Or does punching a "normal" (or off duty cop-horse for that matter) yield the same penalty?
I think they are classed as police property so therefor anything illegal done to them carries a higher sentence, the same applies to assaulting a police officer instead of a civilian, or nicking a police car instead of an ordinary car.
Ah, yeah, I figured that might be the case. Makes sense