Scratch is chicken candy. Don't given them too much. It can make them fat. This would not serve as a replacement for Oyster shell. I don't know anything about feeding them Alfala. The purpose of the oyster shell is to provide calcium for stronger egg shells. Oyster shell is cheap. I can get a 50 lb bag for less than $10.00. I have 33 birds and a 50lb bag will last many months, maybe a year. During the winter when they are not laying very many eggs that don't consume much of it. Right now all of them are laying and they are consuming more but a little bit goes a long way.