A constructed furniture item that could be made from just about any material.
It would act like a one tile food storage container set to only accept raw eatable plants.
Dwarves with the food hauling labor would fill the bin with raw plants if there are any available.
If an animal with the grazer tag becomes hungry and they are near a food bin, they will walk over to it and eat one unit of food on their own, refilling their hunger to max. Unlike dwarves eating food raw, this would not produce seeds when an animal eats the food. If an animal has access to grazing tiles, they will prefer to graze rather than seek out a food bin.
The idea is that if you can't/don't want to provide grazing areas for your livestock, you can keep them alive with a feed bin. It would also allow you to keep animals like elephants alive who normally can't graze fast enough to survive at the moment.
A food bin will be refilled as it is emptied. It can also be forbidden which will not stop animals eating from it, but will stop the haulers from refilling it with more food.
Non-grazers will not consume food from feed bins.
Food inside feed bins will not be visible to dwarves who are seeking either food or plants for brewing/cooking. Deconstructing the feed bin will deposit any contained food onto the floor, making it usable again for dwarves.
Animals will NOT eat food stored in normal dwarven food stockpiles or mature crops sitting on fields.