Ducks and chickens together

[PLUMBER07]

We have 3 ducks a friend dropped off since we have a coop. I have 10 hens but no idea about ducks. They all seem to get along well but I have read ducks need brewers yeast added to the chicken feed. With this bother my girls or should I try and keep them eating separate? That seems to be a daunting task. Any help or experience is appriated

 

[chaschkn]

The yeast is for naicin right? I have a followup to whoever responds: how long after being full grown do ducks continue to need extra naicin (relative to chickens)? I understand its need for bone growth, just wondering if it is a persistent requirement.