I have never candled an egg. Once a hen locks onto the nest, I never touch the eggs again. I do candle, usually at 7 and 14 days and remove any infertile or DIS eggs. Doing so provides more room for the viable eggs and the hen is able to pull them closer to the nest center. Those DIS eggs can cause problems; one broken/exploded DIS egg means the other eggs are covered in foul, bacteria ridden mess. I would rather check to be sure the hen is not brooding for nothing.
I wonder if disturbing the nest to check on the eggs might affect the hen's behavior, or the eggs themselves? Candling takes seconds an egg. If eggs can be shipped across the country and hatch the bit of careful handling during candling is not going to hurt. Any evidence of an upset hen and it's hands off. I do not believe for a second that the one time candling the Tribble eggs caused DIS.
I wonder if Tribbles have evolved slightly different temp or humidity needs that our incubator settings or foreign broody's don't provide? Evolution/change happens because life has to change if the environment changes. Of course selective breeding is the exception. Your birds are quite unique in appearance because you have made it so. I suppose what you write is possible. Is there reason why you think this might be so?
I've got eggs under my broodies due to hatch starting in 5 days. I hope they hatch for you. And I hope to wake up tomorrow to find three little Tribbles. If not, it won't be because I candled them quickly this morning. Crap happens and I'll try again in the future.
