I only know about sheep. They love fruit trees, to the extent that generations of sheep have done their best to destroy my orchard. They will happily eat leaves, twigs and bark. We do have plum trees but I haven't noticed if the also like or avoid plum. Currently though I have two old biddies living in my orchard, and one in particular is addicted to golden gage fruits. The tree was so loaded this year that I ran out of space, and need, to preserve them. Balou the ancient Soay hangs around under the golden gage, waiting for the fruit to drop down - having already picked every gage she could possibly stretch up to. She doesn't eat the stones, but spits them out and my JR crunches them up. It all seems a bit bizarre.
Only the poultry seem interested in fallen apples, but Balou also eats raspberries, gooseberries (Pax, the dessert variety) and any other soft fruit she can get her jaws round.