My views are: Canker. The more you treat for this the more you'll have to carry on doing so. I believe all pigeons have this to a greater or lesser extent and pigeons can naturally keep on top of it themselves, those that cant will be last back to the loft and wont be kept for the following year. I put an Iodine product in their drinker a couple of times a week which I believe aids in keeping the levels low. Worms. Dont think you can stop pigeons getting worms, cant see them being able to build an Immunity against these. Cocci. I see this as a barometer to the pigeons overall health. If it should be a high count all is not well, the pigeon is ailing in some way or has been through some type of stress like the moult or after a tough race. Look for the problem which caused the high count and not for a cocci treatment. Respiratory. If a pigeon gets this remove it from the loft, you can treat it or leave it to its own devices to get over but should it reoccur at a later date remove it from the loft permanently. This is the way I see things, whether its right or not who knows