When we started in goats some 13 years ago we were told the same thing "they could not have cooper". We were told that my 4H leader. We went to a clinic and they said there that YES they have to have cooper and never to buy a mineral that is for sheep and goats because that does not have enough Cooper.
I went back to the 4H group next meeting and they told me that I did not know what I was doing and I was going to kill my goats. We were just in shock that she would say a Vet did not know what she was talking about. (Yes we do know there are some of those out there) but sue specialized in goats, sheep then the bigger livestock. Well the next show we went to the judge dismissed all of their goats and told that they ere so full of worms and they needed copper before she killed her goats. Later she came to me and asked for information.