There are plenty of studies that show feeding Layer to young chicks can and often does cause internal damage. In those studies they cut the chicks open to see what the damage actually is. The problem is the extra calcium in Layer.
But that’s young chicks and it is when all they eat is Layer. I don’t know when they have matured enough for their bodies to be able to handle the excess calcium if they are not using it for egg shells. And if the Layer is a pretty small portion of their overall diet, the risk is not nearly as high.
There are a lot of unknowns about this but there is one sure-fired way to know when to switch, when you see your first egg.
But you have another option. Instead of switching to Layer immediately, offer oyster shell on the side when they are approaching laying age. The ones that need the extra calcium seem to instinctively know they need it and those that don’t need it usually won’t eat enough to harm themselves.
That’s what I do when I have young chicks mixed in with my flock. Feed Starter or Grower with oyster shell on the side to everyone. I hardly ever feed Layer.
