The precedence for this was set by Bueckner v. Hamel in 1994,
http://www.animallaw.info/cases/caustx886sw2d368.htm. "Texas law allows persons to kill without liability dogs that are attacking domestic animals. However, the attack must be in progress, imminent, or recent. This defense does not apply to the killing of dogs that were chasing deer or non-domestic animals.
This past year(cant find the law right now) that made hogs the property of the owner of the land where they are. Does that make sense?