I understand completely what you're saying. Im in no way criticizing you. You did way more than a lot of owners would do. I basically said the same thing as Dr.V
Oh, and it COULD take up to 6 months, but it doesn't HAVE to. Oldhorselady here is already seeing results after what, a week or so.
Do you know where your hay is grown? If so you can ask the grower or the county extension office if there is a selenium deficiency. They can also tell you if Se should be supplemented.