Don't treat for anything. The birds with the strongest constitution will be fine, the others would go down anyway the first hard race they get. The ones not getting over it by themselves should be given short shrift, i know its no everybody's idea on how to deal with things but in 3/4 years of being rigid with this method, you won't get sick birds in your loft. I've been through every emotion, from feeling ill to cursing myself, but its been worth all of them. I simply don't get sick birds from my own stock. This year is typical, i've had to dispose of only 2 youngsters, and they were both bred elsewhere. Very best of luck to you, however you deal with it.