Don't know about other states, but in Texas you can't get into trouble for protecting your livestock. People are suppose to control there dogs.
Here is the actual law. Putting out antifreeze does not fall in the scope of it. Antifreeze is a broad range solution that can be injested by innocent animals that have not and do not intend harm to your animals. Shooting them does though, because it is targeted at the specific animal ( as in dogs) that were, biting, killing or worrying your livestock. I believe in shooting coyotes and any stray dogs that come onto my place that bother my cows, and I don't hesitate to do so.
http://www.animallaw.info/statutes/stus ... 22_013.htm
Texas
Dogs or Coyotes That Attack Animals
Statute Details
Printible Version
Citation: TX HEALTH & S § 822.013
Citation: V. T. C. A., Health & Safety Code § 822.013
Summary:
This Texas statute provides that a dog or coyote that is attacking, is about to attack, or has recently attacked livestock, domestic animals, or fowls may be killed by any person witnessing the attack or the attacked animal's owner or a person acting on behalf of the owner if the owner or person has knowledge of the attack. A person who kills a dog or coyote as provided by this section is not liable for damages to the owner, keeper, or person in control of the dog or coyote.
Statute in Full:
(a) A dog or coyote that is attacking, is about to attack, or has recently attacked livestock, domestic animals, or fowls may be killed by:
(1) any person witnessing the attack; or
(2) the attacked animal's owner or a person acting on behalf of the owner if the owner or person has knowledge of the attack.
(b) A person who kills a dog or coyote as provided by this section is not liable for damages to the owner, keeper, or person in control of the dog or coyote.
(c) A person who discovers on the person's property a dog or coyote known or suspected of having killed livestock, domestic animals, or fowls may detain or impound the dog or coyote and return it to its owner or deliver the dog or coyote to the local animal control authority. The owner of the dog or coyote is liable for all costs incurred in the capture and care of the dog or coyote and all damage done by the dog or coyote.
(d) The owner, keeper, or person in control of a dog or coyote that is known to have attacked livestock, domestic animals, or fowls shall control the dog or coyote in a manner approved by the local animal control authority.
(e) A person is not required to acquire a hunting license under Section 42.002, Parks and Wildlife Code, to kill a dog or coyote under this section.