Bo-Se or other selenium additives, as suggested by your vet or feed company. Feed companies hire nutritionists and other scientists who study feed requirements of the species for which they manufacture feed. Few of us are smarter than these researchers. Unless you absolutely have no other alternative, don't become a feed mixer. Chances are, they know more than you do, particularly since nutritional requirements vary from region to region.
Loose minerals work better with goats than mineral blocks.
Goats tend to chew rather than lick mineral blocks. This is hard on their teeth. And don't worry if they eat it sometimes and ignore it at other times. Their bodies know what they need. Leave the loose minerals out, free choice, and even week-old babies will eat them.