Hi!
I feel nutrition is an art that uses scientific information sometimes.
I can offer what I do, and I will share some of my reasoning (which is not the only reasoning, natch).
I have it easy - no drakes. However, my feeding system would work with them, from what I have read and been told. We started with turkey/waterfowl starter, and I mixed in about 20 percent rolled oats for fiber and a little less protein. At two weeks I began adding grower pellets, till at about three weeks they were on grower, again with some oats mixed in. I also fed and feed treats like a few peas and some salad and slugs.
When my ducks started displaying breeding behaviors, I offered them a half cup or so oyster shell free choice once a week, with a small handful a day of cat kibble (now I wanted to pop up the protein and calories a little, in anticipation of egg laying).
My reasoning: while there is disagreement about proper protein levels for domestic ducks, I went with Storey's Guide's recommendations, to avoid angel wing. Ducks need about three times the calcium of nonlaying seasons (and drakes) for the laying season and, ideally, a month before they lay. This has to be estimated, and I used their behavior and also the clue of milky discharge out the vent to let me know it was time to prepare them for laying, diet-wise.
Once the first egg was laid (at sixteen weeks, three days of age), I started keeping the oyster shell out for them at all times. Some really chow down on it, some poke at it and walk away, a couple don't seem much interested. I occasionally sprinkle some into their feed just in case the ones who aren't getting any might need some. I find they are more interested in it if I cover it with fresh clean water. They dabble in it and I am sure they ingest some while they are playing.
Even though they are the same age, they are developing at different rates. I don't think I will see everyone laying regularly until next month some time.
I have read and been told that by offering oyster shell free choice, separate from their feed, the ones that need it will eat it, the ones that don't won't.
Annarie uses a 50/50 layer/grower ration during laying season, and I have thought of using that approach as well. Right now the oyster shell free choice seems fine. They have laid over a dozen eggs the last couple of weeks (this is the very beginning), and the shells are all very nice. One egg popped out without a shell one afternoon. We were all surprised! But I expect that as everyone begins to mature this first year.
