We recently finished a batch in our "Little Giant" 110v 40 watt "Still-Air Incubator." We do a couple batches in it a year. We use a 42-egg automatic turner and usually fill it with 42 eggs and usually get around a 65/70% hatch rate. This hatch we placed eggs from 2 different sources. We placed 18 from a brother's flock and 24 from our flock. We placed them so that each set of eggs occupied their own row on the turner as much as possible. In other words, his eggs filled one half and ours filled the other half. Now on day 23 and the eggs hatched as follows: 20 of my 24 eggs hatched. 0 of his 18 eggs hatched. I opened all the eggs while burying them. 2 of my 4 eggs were infertile, the other 2 were un-pipped eggs with nearly complete embryos. 16 of his 18 were un-pipped eggs with nearly complete embryos. The only thing I can think it would be is that he feeds his hens under a "don't over-do it" approach. His hens are always frantic for food and they are crowded. I feed mine enough that at the end of the day there is a small portion left in the feeder. I prefer the "as much as they can eat" approach to feeding. We both feed a commercial layer ration. Mine are also supplemented with free-range forage, cracked corn in winter, and yard and garden scraps. What else might it be?