I have in the past used Gary Spavin, Auchincruive, Retford Poultry and De Weerdt. Spavin found no problems and didn't try to sell anything. Auchincruive didn't find much, but also indicated that no treatment was required. Retford have found and recommended treatment, but have also indicated no treatment required on other occasions. De Weerdt I used because I wanted Parastop, so had to have a test. They indicated treatment was required. I vaccinate against PMV and Paratyphus. When new pigeons are introduced to the loft, I treat with Parastop prior to vaccination, thus the need to test via De Weerdt. Like Vinnie, they normally don't get anything except one spot. Except when new pigeons are introduced, they are usually in fairly good health. I am not experienced enough to know otherwise, but if they were really unwell, I would notice without doubt.