My feed is in large barrels that is located in my garage that is locked.  I live alone, so the feed is not labeled because I knew what's what.  I am the only person who feeds my animals on a daily basis.  This relative is a brother and he has a key to my house in the event something happens to me, my siblings have access to my house.  He used his key to get in to the garage area.  When I told him that I was out of town (2 hours away) and that I would not make it in until later that night, he thought that he would help me out by feeding the animals.  As much as I appreciated the fact that he wanted to help, I feel that he should have asked me if I needed help feeding.  I would have told him no because I was going to be home in time enough to feed all of the animals. Instead, he took it upon himself to feed the animals the first feed that he saw.  In his mind, he thought that feed was feed regardless of the type of animals.  He thinks that the manufactures make feed to feed any and all animals.  He doesn't understand the different medications, minerals, etc. can be toxic to certain animals.  He doesn't understand bloating, pigging out on food etc.  He is clueless and that is understandable.  
As far as the feed possibly doing harm to some of the animals.......well, yes, it is possible.  I have read and know that medicated feed can kill ducks.  I have read and know that copper can kill sheep.  I have read and know that goats can become bloated and die.  Well all of the truths were things that could have happened.  The starter/grower feed was medicated and did have copper.  When I got my first sheep years ago, 2 lambs got into a bag of medicated feed and died within 3 days of eating the medicated feed that contained cooper.  I learned my lesson then.  It was a hard lesson to learn and ever since then, I have felt guilty and fully responsible for them losing their lives.  That is why I am so afraid of anyone feeding ANYTHING to any of my animals.  
There are only 2 people that are trained to feed my animals when I am out of town for days at a time.  And 1 of those 2 are my 5 year old nephew.  My nephew will tell his father (my brother) what animal gets what feed and my brother will follow his instructions and directions.  He knows the feed to an exact science (it's scary) but I trained him VERY well.
So this is why I was asking for a Do Not Feed The Animals sign.  In addition to placing a sign on the fence, I will also place stickers on the storage containers that hold the feed so that no one else will try to do me a favor and feed the animals.
P.S.  I think my brother is afraid to call me.  I think he thinks that I'm upset with him.  He had my other brother to call to tell me that he fed the animals "chicken feed".
Am I over-reacting?