I have had marginal hatch rates, too. At first I put it off to shipped eggs. Eggs from my own layer flock I hatched side by side hatched great in the same incubator. Last hatch I got 11/19 hatched of the Cream Legbars set. A few were infertile, a few early quitters and 5 that I eggtopsied that DIS very late--they had begun to absorb the egg sac then died. Not sure why, didn't culture them. I did incise the skin over the skull (calvarium) to see if there was an obvious hernia. There has been speculation in Swedish Flower Hens that late DIS might be due to skull problems from two copies of the cresting gene. In a normal chick, there is a small fontanelle (gap between the two halves of the skull cap or calvarium) that runs down he midline and in these DIS chicks I did find the brain tissue was not protected/the overlying bone was thinner or absent than expected. It could be that the dead chicks had already decomposed several days before necropsy as they sat in the incubator, or perhaps they did not get the extra 2 days of bone growth to make the calvarium thicker. That was really the only thing I saw that was not as expected.
I also had a 50% hatch rate under my broody. So for whatever reason, I am only getting about a 50% hatch rate from my unrelated hens (roos are from 1 breeder, 2-lines, 2 hens are from another breeder--2 lines, one hen is from a 3rd breeder). If I figure out if there is a temp or biological issue, I will for sure post my results. in the mean time, know that you are not alone in your results!
