First I have to say that ‘‘Don’t waste the barley on the geese’’ is probably a better translation of the Romanian expression.
Well, I think they didn’t make the best word choice with this expression. Its meaning is certainly not as obvious as the one of other variations of the same saying, like ‘‘Don’t give jam to the pigs’’, for example.
Apparently, people in my country think that barley is too precious to give it to the geese. I’m no expert, but I think they would mostly let the geese feed on grass, fallen fruit, algae, worms and such and would only give them some corn and stale bread.
So yes, your guess was spot on: when and if they do have some barley, they might keep that for animals considered more important, the way horses are.