blood test question (related to selenium levels)

[Deanna German <finishis2win@columbus.rr.com>]

I know this has been covered extensively here before, and I'm sorry I didn't
pay attention, but suddenly since I want information it has more relevance.
:-)

If I ask my vet to do a blood test next spring when my mare gets her annual
shots, besides selenium levels, what else should I be looking for and what
tests should I ask for specifically? Is having an analysis done costly? In
an apparently healthy horse is it worth it? (Probably is, if only to have a
benchmark to compare to if things start going wrong.)

I know we are severely selenium deficient here (Ohio) and so I supplement.
Through my network of horse friends I had heard to supplement VitE and
selenium at about a third higher than the directions on the supplement
containers. I'm having no signs of selenium toxicity, but without bloodwork,
I kinda feel like I'm shooting in the dark. I guess I'm potentially not
supplementing enough.

TIA!!

Deanna