In this study, samples of 16 dairy cows from a MAP infected farm were used. Serum, milk and fecal samples were collected. Categorizing these cows into two groups based on their MAP infection status different standard methods for detection MAP were applied. Healthy controls showed no positive results in enzyme-linked immunosorbent assay (ELISA) with serum and milk samples (cattletype MAP Ab, Qiagen, Hilden, Germany; In-direct, IDVet, Grabels, France) and after cultivation of fecal samples on commercial Her-rold´s Egg Yolk Agars (HEYM agar, Becton Dickinson, Heidelberg, Germany) for 12 weeks. Cows with positive results were grouped into MAP infected cows. Specifically, for mass spectrometry analysis serum of seven MAP infected cows and seven healthy controls were used. All animals were from the same farm and were kept under the same environmental conditions. For additional mass spectrometry analysis with a further control group sam-ples of 21 dairy cows from an uninfected farm were examined. All cattle from this farm showed negative results in ELISA with serum and milk samples. Additionally, there was never a positive result in regularly tested fecal samples and sock swab samples of this farm. For verification of differential CTSS expression in Western blot analysis five dairy cows from another infected farm were consultedincluded. MAP status of these cows was analyzed by cultivation of fecal samples on HEYM agar for 12 weeks and ELISA with se-rum samples. In detail, two cattle were categorized into healthy controls and three cattle into MAP infected cows. Withdrawal of bovine venous whole blood and experi-mental protocols were approved by the local authority, Government of Upper Bavaria, permit no. ROB-55.2-2532.Vet_03-17-106.