We had this diagnosed via blood tests on a cross section of birds taken from stock,ob racers and yb racers.Our birds flew well round home,droppings were good and looked fine ,but our performances plummeted and birds were comimg back from 100mls.Tylan and doxycycline were used for 21 days together and then the birds were retested , apparently the vet (Retfords Poultry) looks for the antibody production to be non apparent to show the desease has gone. Talking to other fanciers some feel that you cannot move this desease , but touch wood we have moved on this year with 10 first prizes...........any body else experienced chlamydia we think it is a lot more prevalant than people realise and easily missed.