Sampling scheme in the three RDQMA farms. All cows in the three farms were sampled at least twice a year from first calving. At each sampling event, both serum and fecal samples were taken. At the time of culling, animals were tagged with special RDQMA ear tags. When these tags were recognized at slaughter, further samples were taken after slaughter. The harvested tissues included two lymph nodes located at the ileocecal junction and two pieces of ileum, one taken from 20 cm proximal to the ileocecal valve and the other taken from very near the ileo-cecal valve. A final fecal sample was also taken at the time of slaughter.