Use only Selenomethionine and add ALA, but remove Hg fillings first...
Se has 24 different stages only the first few bind with Hg but others not bound to methionine will oxidize and cause issues. In nature only Selenomethionine exists since plants also find lower forms of Se toxic.
However feed lots have a more 'Monsatan' strategy...
Possible expressions of oxidized Se mostly by Hg but also other oxidizers like Miracle-Mineral-Supplement and radiation are here: