Then it could be that the parent birds already suffered from some kind of deficieny and/or genetic disorder and other than providing additional vitamins etc. there does not seem much you can do.Don’t want the corn and soy in their feed for better egg quality as that’s their main purpose. I hatch all my birds and these ducks originated from a breeder (shipped eggs that I hatched). The main thing with Chicken feed was not to give medicated to ducks as they will overdose and die from it but otherwise I thought the ingredients were pretty similar and I had my other ducks on this with no problem. The other ducks originated from a hatchery.
But maybe @Isaac 0 has an idea