I have one old sheep in my herd. We've had her 10 years.
Because of her, I used sheep feed and sheep / goat minerals for years and never had an issue.
Last fall, some of my black goats started turning red.
By spring, some were having worse worm problems than I've ever seen.
Had blood tests ran and they're almost all showing low copper levels, some worse than others.
Now I feed the sheep seperate and am giving the goats range mineral, which was higher in copper than the goat minerals I have available here.
Also top dressing their feed w/ copper sulfate (read it online, tried it, seems to be working for a short term boost...but I don't want to OD them so will be cutting back once their levels are up where the vet and I want.)
Point of the story: It won't always show up overnight, it took years before mine started showing signs of a copper deficiency.