Unfortunately, I don't have advice for you, but I am having the same problem. We have 5 silkie chicks, and 2 of them have this same problem. I have been looking everywhere for advise, or answers, but the only thing I find is info about "Pasty Butt", which, as I understand it, is poop blocking or covering the vent...and this is NOT poop. It's a black, pulsating protrusion from the vent. My other chicks, luckily, don't seem to be picking at them, but they do seem to be constipated. I have been giving them probiotics with their food. We ordered them through the mail, and they just arrived yesterday. I noticed this problem within the first 12hrs of having them. They seem to struggle, and cry when they have to try and pass. I have done all of the suggestions I could find, varieties of soaking & wiping, and different lubes, and they don't seem to be getting any better (maybe I'm impatient, but we already lost 4 of our 18 that arrived - of different issues - but, I am not eager to lose anymore, especially if I can help it!). So far, in all the books I have, and all the online research I've been doing, this post is the only one I've found that is about the actual vent prolapse, and not just Pasty Poo on the bum. It's been incredibly frustrating, and I was surprised that there isn't more info exactly about this problem. I am down to my last straw: going to soak them once more & try some Prep H. Hopefully it will be better in the morning, and if it is, I'll let you know. I'm open to anyone's advice too, so anyone who knows what this is, or how to fix it, Please! Drop a Line!
Oh! but one last question: Can this be caused by the hatchery attempting to sex the chicks, before sending? I ordered straight run, and the thought has crossed my mind that they through in the rejects of their pullet guarantee, after squishing their insides.
