We have five hens. Rhodies. They were given to us so we are unsure of their age. One hen,suddenly began to lose weight and condition.She developed a strange swinging action of her neck from side to side.It became apparent,she couldn't see. She was reluctant to walk and began taking herself off and hiding,sitting all day.We isolated her,she had yellow diarrohea.After 3 - 4 days,the faeces were white,then a blackish colour,then began to return to normal.She began to put weight back on.She is now back with the others,grazing again,but at night,we put her in a separate pen because she still can't see. That was from mid December until 1st week of February. Now,a 2nd chicken,who was VERY robust,seems to have come down with the same thing. We are repeating the process. Whatever it is,it must take quite some time to incubate - the other 3 are just fine. The coop is clean,we maintain rodent control. They are fed 3 types of grain and lots of treats.We have not changed their feeding habits. The Vet hasn't got a clue. We are just woried that they will all eventually come down with this and all be blind. What is it and what can we do??