At a guess 50 chicks, from 2 months down to 2 days. It's ridiculous everyone I've spoken to personally has had this done & yes the person showed up and tested every single bird older than 16 months.. But no way did they say you can't have chicks. Chicks are hatched from my birds from my eggs. No they aren't kept in same pens but in the same yard. Personally I think this rule is getting confused. Yes for first time testers all flock members of laying age have to be tested. But it never says you can't have chicks younger than 16 weeks on the premises. Once you've been tested in every following year they only test a certain percentage or a bird from each breeding group. That is my understanding on how it is supposed to be done.