Sharon, unless they have dead embryos already after 6 - 7 days, I boil them, mash them up fairly fine, shells and all, and feed them back to the laying flock. They love it. Be careful to break them slowly, as sometimes a little liquid will tend to squirt. The mixture smells fine, and apparently tastes great to the chickens.
I do much the same except I've done it for eggs as old as 14 days or more. I crack all the undeveloped and/or partially developed eggs into a glass bowl. Then I nuke all the shells for about 3 minutes or so on high. This cooks all the stuff on the shells and makes them really easy to crush up into very small pieces. While the shells are nuking, I scramble all the eggs together, add a little Rooster Booster, and a LOT of Cayenne Pepper. Then I take the eggs shells, wrap them in a paper towell, mash the dickens out of them, and sprinkle them over the top of the eggs. Then nuke the whole things for about 30 minutes on low. And Voila! Egg soufle for the hens. And as Mike says, they love it.
God Bless,