Ihave a large flock of mixed breed chickens. About 3 mos ago one girl lost the use of one leg. Since then approx once every 2 wks i find another lady with the same condition. I keep very clean coops. And it only seems 2 affect my red and buff girls. What the heck is this. They are otherwisw healthy. Eat drink and lay as normal but after a few weeks hobbling on one leg they die.