Calcium gluconate gives them calcium of course but also helps the egg pass on through it works on the muscles to help the duck lay the egg.
https://www.backyardchickens.com/threads/calcium-gluconate-for-egg-bound-ducks-preliminary.959537/
we found out about cal glu from a member
@Amiga when one of her Runners was egg bound the vet gave her cal glu to help her pass the egg.
also
@Aunt Angus can verify how well it works when one of her ducks was egg bound.
@DuckyDonna
what is a bloody egg duckling please explain