Walter most top lofts will tell you they don't treat for anything. Again it all depends on what system your on . And what I mean if your on w/h cocks are out do their exercise and straight back in the loft same for roundabout pigeons. With natural pigeons as you know no matter how much work you give them ie training/ flagging you always give them a bit of open loft . That is when they pick up canker .
Walter and before you say are you on the gabby water . I think you are getting a bit mixed up about canker and coccidiosis. Pigeons get infected with canker . But always have some amount of coccidiosis in them so their system can learn to fight against it .