I'm thinking your problem is a hawk. The smaller predators will normally start eating the head. A coyote will grab the entire bird and take it to a "safer" location to eat it. If it were a dog, you will find several dead birds with nothing eaten at all. I hope this is helpful to y'all.
I think the main advantage to distillers grain is that the fermentation process begins the digesting. Another thing to avoid is the genetic modified grains. There is all kinds of nasty stuff in them. If you can find feed that has probiotics as opposed to antibiotics is
the next thing,