It could be the feed. Chickens are very acute to changes in their environment, and no egg-laying is usually an indication of stress. This isn't the normal time for a molt, so this could be from the feed. How did you implement it? Did you just stop giving the old feed and begin serving the new feed? Does that feed have the proper nutrition, or should supplements like calcium/oyster shell be provided? What I would recommend...go back to the old feed and see if they start laying. Then gently phase in the new feed. Offer both...begin mixing the old feed with the new, and then gradually offer only the new feed. This is more of a seamless transition that should help the birds get used to it. When I switched from crumbles to pellets, I did it in this fashion (granted the recipes were the same), and the birds didn't notice a thing.