My neighbor has this really annoying cow that always crosses the fence and today I slaughtered the cow.
What made you think it was morally acceptable to slaughter a cow?
I killed that cow because it was fucking annoying.
People who harm animals go after someone they perceive as weaker. If you had an issue with the cow, you should have called animal control instead.
It's just a cow and now my neighbors know.
You shouldn't view it as just a cow. Especially since it belonged to your neighbor. It seems you may have problems controlling your anger, I would recommend seeking professional help.