Just a few thoughts: I would go with 600 mg.

Is the duck drinking? Anytime one of my birds were sick they didn't drink-therefore wouldn't get the medicine, plus as with anything added to the water or food you can never be certain exactly how much of the medicine they are getting unless they ate or drank/ingested ALL of it. I'd find another way to administer it. Not sure if you can give the medicine orally to the bird or not (600 mg in a syringe & forced down the beak, or on some bread?).

I'd put a topical antiobiotic on the wound. Watch for fly strike, maybe use SWAT to keep flys away.

I know that doesn't answer your question, but hoping is helped in some small way. Good luck

Brendasue

I simply don't know, but I do know that you can not give medicated chick starter to ducklings. That would indicate to me that there is some sort of antibiotic sensitivity to some specific antibiotic in ducklings.

I suggest that you find out what antibiotic is in chick starter and do not give that one to your duck.

Big time warning here: if the package does not give the dosage for ducks, the medication is not approved for use in ducks. That might mean it is not tested in ducks, or it might mean it's not safe for ducks. Although if it is really bad for ducks, there might be a warning that says not to administer to ducks.

The only antibiotic I have in my house right now is sulfadimethoxine and it doesn't say it's for ducks, either.

You can use a topical antibiotic to hold the fort until you find something safe to give to your duck.

best luck to you and the duck.