As long as the filltype is unloaded in a form the animal pen accepts you should be able to add any fillType from base game and map to the foodGroups.
So if it is a bulk product you can dump you are usually fine. Most animal pens do not accept feed as pallets.
For instance on the Judith Plains map, if you add dry corn (MAIZE2 in JP map) and corn flour (CORNFLOUR in JP map) to the pig base food like this:
<foodGroup title="Base food" productionWeight="0.500000" eatWeight="0.500000" fillTypes="MAIZE SORGHUM MAIZE2 CORNFLOUR"/>
you can dump dry corn into pig pens without problems. But adding corn flour pallets won’t work unless the animal pen has a pallet trigger or you can somehow fill a trailer with flour and then dump it as a bulk product into the pen.