Another forum I'm on, somebody asked a question about fertility. Eggs from their own birds. Said they weren't developing in the incubator and sometimes they were getting only one developing egg out of a whole batch.
Poeple gave various advice about feed, trimming tail feathers and checking the males were actually treading. Then the OP mentioned that he gave eggs to someone else, and they all developed. So it looks like the eggs ARE fertile, and that there's a problem in the incubator.
I said I thought the most likely cause of known fertile eggs not developing at all would be a temp spike in the first couple of days that killed them off before they even had a chance to start developing.
Is there any other cause that anyone can think of?