Barley is only about 12% protein, same for wheat. The layer feed is usually around 16%, so you'd be feeding them (without doing the math, just a rough estimate) about 13% protein...which can certainly affect their laying rate. The ideal would be 16-20%. (16 is usually adequate but I prefer a higher protein ration for my birds) If they are free-ranging and able to make up the protein deficit by eating bugs (which is difficult this time of year, the bugs are not really out) then they'd do all right. But if they are confined and this is all they are getting...yeah, they are probably not going to lay as well. If you want to go the whole grains route of feeding, you will need to add a protein source--field peas, soybean products, and fish meal are all high protein ingredients you could add to the mix. Or you could just give them small amounts of the grain alongside the layer feed if you don't want to get into the math involved in balancing your own ration.