I have a very mixed flock. It consists of 9 pullets 18 to 20weeks old, 3 pullets 8-9 weeks old, and 2 ducks 18 to 20 weeks. I am concerned about nutrition. I was wanting to continue feeding the flock raiser crumbles that they have been raised on and just add oyster shell seperatly for the layers but not sure if everyone will get the proper nutrition this way. Any thoughts?