Fluid Filled Sac on Rear end

[Euphemia]

I have a three day old Cream Legbar pullet I paid big bucks for that has showed no signs of sickness or paste butt. However this evening I noticed a fluid filled sack protruding from her rear end. It did have some poo on it. I washed it off with a war compress. I have never has a problem like this in the over 100 chicks I have raised. First, what is it? What is it caused by and what can I do for this little thing? The brooder is at a good temp. No draft. She has been eating and drinking well. Does not at this time seem to be in any distress at this time. I offered egg this evening. I don't know what to do. Any input would be so appreciated.

Thanks

Eupemia

 

[fogandcopper]

I am unfamiliar with this except in hens old enough to lay. In that case it is often laying gone wrong.