apples work well for this but i find
chickens will only eat so many fallen apples. its best to mix up the
trees and there fruit drop days, we also use pear, peach, plum, mulberry, persimmon and a few others. now i get a more diverse amount of fruit and so do the chickens. well be expanding to geese next spring.
when searching for an apple that will drop fruit for livestock i look for ones that hold fruit long into winter. apples can supply fruit much longer into winter than any i know of in my climate. persimmons are late and will still be dropping in now in december, but real high quality apples wont even be finishing until december here, the last ones drop in feb or march. its great if you can get one that taste excellent and heavy fruiting.
i live in an area with lots of wild apple trees and trees planted by settlers here a hundred years ago. i have no names but graft the ones i like at home. its a very easy way to get a lot of high quality trees cheap.