What kind of turner do you have? Maybe someone could help you with your specific model. My turner for the Hovabator 1588 has slipped out of the tracks couple of times, generally at the very start because I don’t get it together exactly right when I set up the number of trays. That’s operator error on my part. And they move so slowly you’re not always quick to notice it’s not moving. Aggravating for me since in my case it’s self-inflicted.
Turning serves two purposes. As Amy said, the yolk or developing chick can settle and touch the inside of the shell. The shell is porous so the yolk or chick can dry out where it is touching and get stuck. They can’t move to pip when that happens, even if they continue to develop. That’s not going to happen immediately but over a bit of time.
Another place turning helps is to get the body parts to form in the right places. That doesn’t mean parts will always form in the wrong places if you don’t turn them, but it is certainly possible. You can get deformed chicks or more likely chicks that die late in incubation but before pip when they start to depend on their body to work right. There have been studies that show turning three times a day is enough but it’s really better if you can manage a few more. That’s one reason I like the autoturners. They may be slow but they do turn them several times a day if I hook them up right.
By Day 14 the body parts have formed and a membrane has formed around the chick (the same membrane that can shrink-wrap a chick if it is too dry) to protect it from contact with the sides of the shell. Turning helps that membrane develop. It’s not long after this they are so big they can’t avoid touching the inside of the shell, so you can stop turning after 14 days if you want to. It doesn’t hurt to keep turning, it’s just that you don’t have to.
I don’t know how long or when yours was not turning. I once had one go a full day not turning before I noticed and I still had a good hatch. Not turning does not guarantee you total failure but it certainly is not a good thing. One sign this might be happening is that chicks die in the third week of incubation.
Good luck in working it out.
