Here is more on medicated feed and ducklings:
Storey's Guide to Raising Ducks, 2nd Edition

Source: https://books.google.com/books?id=s...guide to raising ducks medicated feed&f=false
Thread source here:
Is Purina Medicated Chick Starter Safe for Waterfowl?
post here:
Storey's Guide to Raising Ducks, 2nd Edition
Source: https://books.google.com/books?id=s...guide to raising ducks medicated feed&f=false
Thread source here:
Is Purina Medicated Chick Starter Safe for Waterfowl?
post here:
Hi Kathy –
The issue here is not so much one of safety as it is one of regulations. Amprolium, the medication present in our medicated chick starter, has never been approved by the FDA for use in waterfowl. Therefore, we cannot legally recommend its use for these birds. However, veterinarians have been using it very successfully off-label for years as a coccidiostat for all kinds of birds, including waterfowl.
The fear of medication for waterfowl dates back to the early days of medicated feed, when sulfa drugs were used. Waterfowl typically eat more than chickens do, so when they ate feed medicated at a concentration that was ideal for chickens, they tended to over-imbibe the medication, which was often fatal. Amprolium is not a sulfa drug and does not have that effect.
Start & Grow is formulated to meet the growth needs of baby chicks until they reach 18 weeks of age. We recommend Start & Grow for chicks and Flock Raiser for waterfowl or mixed flocks. If you feel your waterfowl need medication, consult with your vet to determine what would be best for them.