I use oak leaves as bedding for my birds. They're free, except for the gasoline I takes me to go around the neighborhood and gather them up. We have many oak trees here, mostly red and black oak species with relatively small acorns. The squirrels take most of them, but my birds LOVE going through the oak leaves when I put down fresh bedding, searching for the acorns. Apparently, if your a duck, chicken, or turkey, acorns are a tasty treat. To my knowledge, the birds appear to just swallow them whole, and I have to assume they are broken down in the crop/gizzard in order to release the nutrients.
Pigs are another thing that can be fed acorns. At Costco.com, they had a 12 lb Spanish ham advertised for $549 plus s/h, said to be from some artisan processor, and made from an heirloom breed of pig which is finished on acorns. I would hope it's delicious, but I'll never know, because the kind on sale at Kroger's for $1.17 a lb is more in my budget.