The low protein food at this point in their lives in not killing them. It might slow some growth down, but it would take a lot longer than 1 1/2 weeks to till babies eating low protein food. Something else is going on. Either they are at the wrong temperature, there is a draft, they are killing each other or some illness is killing them. Keep the brooder as clean as possible, keep poop out of the feed and water and make sure the area around the water is dry. Cocci loves to live around here. Double check your temps. Make sure the temp at baby head height is correct. The use of one big bulb is better than two small ones. That way there are places to get out of the heat and one big good source of heat. Set the temp about 92 degrees.