I had a lot of pasty butt issues during the very hottest time of the summer with broody chicks. The Pennies. It was in July and there were a few weeks of REALLY hot temperatures for our location. I kept watching them and picking off the poop on some. I don't soak them in warm water.. I just clear the vent. None were 'that' bad.I used to worry about giving the chicks milk products when they were young but I finally realized that the amount I would give a chick was so small that the calcium issues were really not a big deal. I was judicious about not giving too much, though.
I'll bet Delisha or Mumsy may have some input on the pasty butt issue. I know we've all heard that acidifying the feed and/or water w/ACV helps with that but I don't know if it really does or it it's just something we all believe. Either way, it sure can't hurt for them to have the ACV!
I kind-of have a hunch that it is the kind of feed that is given the birds that cause the pasty butt but it's only a hunch. I know when I was giving a good amount of raw meat to the new-hatches throughout the week I didn't get pasty butt at all. I did get it, however, on my first batch that I gave very little raw meat to. Not sure if that was a factor or just coincidence
In conclusion, I think too much heat is a big cause of pasty butt.