What I have read is that mash is difficult for ducks, as it falls out the sides of their mouths so much. Mash is a dry feed. Moist food works well for my flock. At this point some may want to advise caution about wetting feed, as there is a risk of mold. If too much feed is set out, yes, it can mold, and in hot weather it can mold quickly. So we have covered that.
Vegetables are good for ducks, especially fresh veggies - as an addition to their balanced ration. Carol Deppe writes about feeding cooled cooked potatoes to her Anconas as part of their diet. And I believe that cooked sweet potatoes can be beneficial as a small part of a duck's diet.
I would love for someone who is expert in waterfowl nutrition to come out with a couple of publications. One, would be the actual amount of each nutrient or component for optimum health. In other words, how many milligrams of calcium, niacin, etc.? And then, more important in a way, some examples of whole foods - not store-bought concentrates - that would meet these requirements. It may take a second kind of expert to produce the second publication from the first. But I would pay money for that second publication. If anyone knows of it already existing, please let us know.
One way to provide nourishment for less money is to get a worm farm or black soldier fly larvae farm going. Those do not take up much room. They require some knowledge, time and effort, but once you have it up and running, provides protein and B vitamins.
I plan to grow amaranth and millet in the garden this year - those provide some minerals, vitamins and protein as well.
Speaking of plans, I really, really, need to get the wheat berry sprouting system up and running. Like, a month ago…. sigh.