I think that as far as cats/dogs are concerned, we have to be even more "experimental" than with ourselves in that there is no "protocol" (that I know of) that people are following. I mean, I know ppl put 1 or 2 drops of Iodine
solution in pets' water, but that's about what I know...
Selenium is not that hard because brewers' yeast is a very common supplement for pets (usually cats love it) and it's a good source of selenium. But I've been giving my cat some of mine (1 pill diluted in water) and give him some of that with a syringe, not much. Yesterday I read (I think in the pets forum) about the good of giving them vit C, so I started, especially since I'm giving him Lugols
(almost a drop daily, trying to heal an allergy, it's working fine, not totally healed yet, but MUCH MUCH better). They said (really, I forgot the origin of what I am quoting) to put crystals of sodium ascorbate in their food (didn't mention quantities), that they will love it 'cause they know they need it (it was specifically about cats). I was happy to find out about that. I'll keep researching...
Well, I hope this helps in some way... :)