Why aren't my eggs hatching?

[sgps]

For years, I have tried and failed to hatch out my own chicks. I have changed out the rooster and the hens. All of them are the same sized birds, with only 10 hens to a rooster. I can't figure it out! I have put them under several broody hens, tried my incubator several times, but still nothing. To test out if it was just the hens and/or the incubator I purchased eggs, and they hatched out just fine. I tried cleaning some, and leaving them untouched, still nothing. Then I tried my duck eggs, and they hatched out well. What am I doing wrong?

 

[Ol Grey Mare]

Is it that the eggs are not fertile (no development ever takes place) or that the eggs are fertile but not managing to complete development and hatch? Did you ever not ANY development when candling? Have you cracked some eggs that came from your breeding pens to check the germinal disc for signs of fertility?

 

[sgps]

I have tried candling and there is very few that develop, and I rarely see any rings in my yokes.