I raise Swedish ducks on a budget.
Ducklings begin on flock raiser (18% Dumor) until they're well-feathered to take the cold (usually about six or seven weeks), then I supplement with free-ranging (our pond is infested with snails, which the ducks swallow whole; they actually get more protein after this begins.) Slowly wean off of feed at ten-fourteen weeks until only supplementing their diet with whole, not cracked, corn at about sixteen weeks. In November, begin moving them back onto a 17% feed mix (oats (11%)/game bird starter (24%)/corn (8%)) and free-feed only this while they're penned from December through mid-March, at which point I begin to wean them back onto free-range again, though exact schedule depends on the weather.
Additional nutrients (except for oyster shells) are provided only as medication.
Laying ducks seem to do well using snail shell and oyster shell for their calcium. Due to the very fishy taste of the eggs (snails!) non-hatching eggs are fed right back to the hens as a protein supplement.