Well, kind of hard to say. Starting with the silver laced Cochins, as I did. If a hen had good type, and kept good clean lacing, she stayed in the breeding pen, regardless of age. Several of these ol gals lasted well past their best laying years, skewing the percieved rate of lay for the group, but helping to cement proper lacing in the line. It was this line that was accidentally crossed with white Cornish resulting in the start of this "project", so I don't really have a good starting point of reference.

As for fertility, I don't remember that ever being an issue. But it does make me wonder. Early on I was dealing with the short Cornish leg issue. I was trying to breed away from it, but until I introduced the Brahma blood it would still show up occasionally. I don't remember a high incidence of dead chicks before hatch that I read of with Cornish, or Japs.