They don't specify restrictions on size for Hero's feast or Dream Feast, so just treat the animal as the spell says.
Goodberry is a bit more complicated. Large creatures are about 8x the size of a medium creature (2x2x2 vs 1x1x1 square).
I don't believe there are rules on it... but you could consult the Ultimate Equipment guide and look at weights for animal feed vs humanoid rations maybe?
They list it at 10 or 5 pounds, for herbivores and carnivores respectively...
Rations are about a pound for one day. So an argument could be made that they require five to ten times more. I would ask your GM.
I think in our games we say about 4 times more food, the assumption being that magically prepared berries are more efficient than a bale of hay or preserved meat...
Let's say a character casts Dream Feast on a horse. Does that provide enough nourishment so that the horse wouldn't have to be fed that day?
Dream Feast gives one meal. How often is a horse fed?
How many Goodberries would I have to feed a horse to sustain it for a day?
Goodberry gives one meal per berry. How often is a horse fed?
Can I feed my character's horse from a Hero's feast?
Heroes' Feast does not feed you. Your horse gets the benefits, but will still need food. Besides, how are you getting your horse to sit at the table? :-)
/cevah