Hi, welcome to BYC!
Rice and corn neither one are appropriate feeds for chickens as they are WAY too low in protein and don't have much other important nutrients like amino acids vitamins and minerals. So it *may* be a fine source of energy if supplemented correctly. It would certainly not be MY choice.
While soy is higher in protein it is a plant source and chickens NEED the amino acids derived from animal sources. I'm not personally fond of soy or the way it smells and I don't know how well birds digest legumes... I am no expert!
If I was gonna feed either... I would likely go with sprouted and maybe grown into fodder, a usual 7 day turn around. And I would only use it as a treat or for enrichment at not more than 10% of their total daily ration.
So to explain a little, feathers are made from 90% protein and it's amino acids. Plus protein is used to build muscle during growing. And eggs that are produced are 34% protein by energy. Point being protein is key and chickens should really never be less than 16% in a non growing bird.
What kind of chickens are you planning to feed? Broilers, laying hens, juveniles, dual purpose breeds?
I do use dry rice hulls bought at my local feed store as bedding in some of my coops. And I might consider using ground rice as a bedding for my live meal worm colony. I would definitely try to find ways to use a product I had ready and affordable access to! Just not at the cost of my birds health.
