I'm no help, I buy any past-by oranges, satsumas, etc, that I can get as Meg absolutely loves them and can peel them with her nose in a little under 20 seconds! (She doesn't eat the peel but loves the flesh.)
A small farm I used to help out on used to get all their local Sainsbury's past-by non-meat food - a trailer-full twice a week. I was instructed to sort onions, leeks etc out and put on the compost heap (if not edible for humans), and to put potatoes and parsnips to one side for boiling before feeding, but as far as I remember they got all the citrus in amongst everything else. They had 4 or 5 sows and their offspring, fattening all the weaners themselves (with a lot of help from Sainsbury's!)