open barrel (trough)

How it works
Rather than having a chest inventory, you would right-click it with any food item to fill it (but only with the same food item per barrel). Similar to the composter, it would display several 'filling levels'. Despite being a new decorative block, its real purpose would be to serve as a trough for animals. Animals would eat their favourite food out of the open barrel, decreasing its stage until it's empty. 

Crafting
The crafting recipe would be the same as for a normal barrel, except without a slab on top. Additionally, you could convert a barrel into an open barrel by removing the lid with an axe (only when it's empty). In reverse, you could convert an open barrel into a normal barrel by adding a slab (again, only when it's empty).

Redstone and technique
This barrel could be filled up with hoppers and would work with comparators (different "filling level" = different signal strength).

Why should it be implemented?
Players could build automatic animal reproduction and food farms and use it as a decorative block.