i think that's just the concentrated goo left over from the egg whites that didn't get used up. most chicks have that i've noticed. on average i haven't seen any problems when that happens. when i have problems it's because the umbilical wasn't totally closed up. usually because they hatched too fast.I'm new to this hatching thing so, I don't hatch near the #s that I've seen on some of these post. I would love too thought (my husband would not be to happy. lol). Anyway, out of 11 eggs that I set I hatched out 3 beautiful turkens, 2 AmerOrp, 1 Orpington, and 1 mystery bantam. Thought that was pretty good for a beginner 7 out of 11. This is actually my 3rd hatch in 3 weeks, but I still feel new. I had 2 Ameraucanas that had internal pips when I checked them before lockdown, but nothing happened. I'm not sure. I'm pretty bummed about loosing them. They are beautiful.
I have question for these professional incubator/hatchers (me being jealous): I had a chick hatch with some kind of yellowish stuff coming out of its rear end. What is going on with it. I had a JG that did that last week and it died after 3 days. I have searched the site and found very little about it.
and i don't really think any of us are 'pros' at this. we just tend to have a bit more experience with the problems that can happen along the way, and grumble because mother nature doesn't cooperate with us very well regarding the weather (temps and humidity).
i'll never be a pro, tho i have learned the ins & outs of my incubators and adjustments i need to make to compensate for the seasons/weather/etc.