Hello: I am trying to figure out how much food to buy in bulk for my 80 chickens this winter. I want to buy from a feed mill in my area but need to know roughly how much to buy so I can price it out. I have several different breeds "heavy breeders", if this plays into it or not. Can anyone help with this? Thanks in advance! Ps: Is grain screenings something I should look into? And what exactly is it?