One of my rouen/pekin cross ducklings has something on his vent and has had it since he was in the egg. I'm not sure if it's just a bad case of pasty butt or if it's something else
We had to help him out of the shell because the membrane was starting to shrink wrap on him. He's able to eat and drink, and I'm unsure if he's even pooped yet, because I've kept him in the incubator because he has trouble walking.
I think it’s unabsorbed yolk, but it looks quite dry already. It will continue to draw into the body some, and will scab and eventually fall off. A little dab of antibiotic ointment can be used to keep it a little moist and help with possible infection.
Keep it on something soft and as immobile as possible, so it doesn’t drag it out or rip it open.