Hi, I had a one day old chick pass today. This is our second incubator hatch but the first time we only hatched one chick so no issues. This time we had 14 and counting hatch. They all seemed happy and healthy, but I looked into the brooder and a chick was sleeping on its back. She was breathing but when I picked her up, she didn't seem well. She was breathing heavy and only had very jerky movement and few. We gave her poly vi sol mixed with nutridrench but she pretty much passed while we were trying to give her the supplements. This was within a few minutes of seeing her on her back. I'm interested in the potential cause in case it is something I can prevent in the future. She seemed to hatch without issue and stayed in the incubator until dry and fluffy. She was transferred to a rubber tub brooder with pine shavings and a paper towel layer on the top with a nipple waterer and some scratch. She was moved to a different brooder with a chick who has a foot that's curled in and taped flat because I wanted the injured chick to have company. She was monitored to be sure she wasnt trampling or picking at the injured chick. All was well. That brooder was the same aside from a small shallow dish of water instead of the nipple waterer. Temp reads 90 degrees to the side and chicks are spread throughout brooder. They were each handled by myself and my 6 year old very carefully. We inspected their wings to sex them, and I flipped most of them over to vent check them. I referenced youtube and google to try to help identify the sexes, and that's when i saw vent checking by flipping them over could be dangerous. I'm wondering if that's what killed her? I also noticed when vent checking her and maybe another one that she had 2 red spots, one was the vent and the other appeared to be her belly button. Once she passed I read about umbilical infection and she did seem to have swelling and redness at her umbilical site (I have pictures of the umbilical post mortem). The rest of them, you cant even really see an umbilical site. The eggs were not washed when placed in the incubator. Some of them had visible debris from the nesting box. I wiped off what I could and a few eggs still had a small amount of dried mud/dirt/poop on them. I also noticed while vent checking her, there was a tiny sliver of pine on her vent, I tried to blow it off but it appeared to go inside. She was 24-36hrs old approximately. I realize chicks are fragile and you cant bat a thousand but if it's something I can prevent, I would like to. I was hesitant on putting the dirtyish eggs in the incubator - can this be that detrimental. Also, I didnt realize vent checking them could be dangerous. Any insight is welcome.