You are spreading misinformation, laws are different state by state. In missouri you can not legally kill someone else's livestock for wondering over to your property, there has to be real damage or loss not just a perceived threat. I had a neighbor threaten my goats and call the cops on me for "damages"( literally just goat poop in there outdoor kitchen area), they told her to build a better fence if she doesn't want animals wondering onto her property and told me if she gives me any trouble to call them and they would deal with her.
It is 100% your responsibility to keep your animals on your own property and your neighbors have every right to do what they need to in order to protect their flock and their business.