Sometimes indoor ducklings have trouble digesting real food (as opposed to crumbles or pellets) if they've had no grit. But if they're outside on the soil, they are probably ingesting plenty of sand and small gravel sized soil particles that will work as grit. Good news!
I've done a couple of different things with their feed since they were about four months old, partly due to availability. I have continued to feed them a grower/maintenance ration with free choice oyster shell (all girls, all laying most of the year) and a handful of dry cat kibble to pop the protein up a tad. We tried going to a commercial layer feed, but they didn't eat much of that. So, back to g/m plus oyster shell.
I started switching about six weeks ago to an organic poultry laying mash. Now, possibly unrelated, one of my ducks is having difficulty with low calcium, in spite of my including oyster shell in their feed pan as I switched over (slowly replacing the former feed with the new feed over the six week time frame).
I feel that a good base complete ration with added variety of fresh and foraged foods is good for the ducks. In our flock, I've found that some tweaking needs to be done for individual ducks (not always easy) to keep everyone healthy.
