Having had dairy goats for 25 years, up until about 7 years ago, we always knew about selenium. Goats required it and we bought loose grain minerals with selenium to mix in with their grain. Michigan soil is very low in selenium and goats can get what’s commonly called white muscle disease. Selenium is very important. Your extension service or elsewhere on the internet could tell what states are low in selenium as far as vegetables and animal feed.
Re Selenium:
I’m going to visit a local feed store and check out their supplement section.