I am extremely new to chickens and with the power of the internet and friends am quickly learning. My situation is this, I have raised a young flock from two days old and have grown quite attached. We just recently got 6 laying hens from a neighbors flock who are all 8 years old. We were assured they were all healthy because I would not have taken them if they weren't. Out of the 6 new ones (I am still trying to properly identify them all) the two in which I think are RIRs are not laying. Tomorrow will be a week that we have had them. One of them has what appears to be a very dirty rear/ vent and getting worse. I have watched all the birds at lengths of time and no one seems to have an issue with lethargy, depression, lack of appetite or bloody stools. My next step is to quarantine the one who's having the diarrhea and clean the coop. Does anyone have any thoughts as to what this could be? Should I quarantine both the girls who are not laying for fear it could be contagious? Could it be old age? Please help out a new chicken mommy.