I get this every year nowt works but my dad has had pigeons all his life 78 yr he’s never had yb sickness ever think it’s down to the number of YBS we keep he only keeps 18 max this year he only has 11 I have 60 but had 80 birds never been anywhere apart from round the house over a week I had to take 20 out the game 20 I bought in does that tell u something all mine were fine also I’m getting grills for the floor as I believe picking about the floor gives them a higher risk of illness