hi,
had the problem with so called feather rot afew years back tryed everything ivamec,copper sulphate,parrafin,harkers dip, you name it i tryed it none worked came back every year. sent samples away of feathers one came back saying it was a fungi problem similar to ringworm treated it with vircon s cured it straight away.put 50grams in a gallon garden spray. warm water spray thechest area and back of neck saturating the areas dont rinse but give them abath a few days later spray the loft and utensils with vircon s problem solved. you can add vircon to the bath water. this will definetly cure the problem. do all the birds in your lofts old, young, and stock.