Silos shouldn't be emptying each day unless they have very little hay. Each can hold 240 hay.
Also, silos essentially ARE hoppers for the animal buildings... and the animal buildings all have a "hay hopper" in them, where you can take hay from the silos from inside every building, and then put it out on the feeding bench. They're better than the new hoppers too, as they can be anywhere on your farm and still function. If you have more than one, they function as a collective. (If you have two and check, it doesn't list just that silo's capacity and inventory, but the total hay in silos and the total silo capacity.)
If you want the feeding bench to be auto-filled, upgrade your barn/coop twice. The second upgrade includes the auto-feeder where hay is taken from your silos or the hay hopper and put out on the bench for your animals to eat if they need to, and all without you having to do anything except make sure the silos have hay in them.