Grass types that uptake selenium in higher amounts are:
Reed Canery grass
Napier Orchardgrass
Brome grass has decreased amounts of concentrations.
Legumes with higher blood selenium concentrations are:
Of course Alfalfa and Birdsfeet Trefoil
Legumes associated with lower uptake are:
White clover and Ladino clover
Why deer seem to go to pastures with these, I have no idea. Just have noticed this through out the year when checking them to run cattle in them.
Selenium deficiency in cow/calf herds has been linked to decreased reproduction performance, retained fetal membranes, increased disease susceptibility and mastis.
Hope this answers some of your questions.