I believe that almost all commercially made feed has some amount of grit in it for digestion. But, I don't know what it would hurt to offer them a little bit of fine grit when they're small. I would use something very fine, like finch/parakeet grit at first, then graduate to larger sized as they grow.
As far as blackhead goes, its really hard to say. The organism that causes it occurs in the wild in various bird species, but in pockets. Some areas have it, some don't. You could probably call you country's cooperative extension service, your state department of agriculture's poultry inspector or veterinary inspection service and just ask them if blackhead is known to occur in your immediate area. Even if it is or isn't, there's no guarantee either way. If you let them free range on ground, they could eat worms, which are the vector for spreading blackhead. Perhaps you might want to invest in a bottle of Fish-Zole and just have it on hand in case you see symptoms develop - odds are you will never need to use it.
