I also have difficulty speaking only in terms of protein level, it must also be done in the context of amino acid profile, especially those that the chicken cannot make enough of on its own.
I have some interesting experience using live mealworms. On several occasions I, or my son, has provided underweight chicks with free-choice access to quality starter feed and live mealworms. The live mealworms are handily the preferred item. The live mealworms illicit a feeding response even...