Aims: The purpose of the study was to compare the growth of Mycobacterium avium subsp. paratuberculosis (Map) and the degree of contamination on Herrold's egg yolk medium (HEYM) and modified Löwenstein-Jensen medium (LJ). Methods and Results: Culture of 2513 faecal samples from dairy cows was performed on each of the two media. The media were read after 5, 8 and 12 weeks of incubation. Overall, the proportion of contaminated samples was significantly higher on LJ (14AE2%) than on HEYM (13AE2%) after 12 weeks but the degree of contamination was slightly less on LJ. After 8 weeks of incubation, only 1AE0% of the samples were Map positive in LJ with 4AE9% on HEYM. After 12 weeks of incubation, 3AE3% of the samples were Map positive in LJ whereas 6AE9% were positive in HEYM. All suspect and culture positive samples were confirmed by IS900 PCR. Conclusions: HEYM supported growth of Map significantly better and faster than LJ, however it could not be determined conclusively which of the two media that provided the highest degree of decontamination when the incubation time was also included. Significance and Impact of the Study: HEYM should be the primary medium rather than LJ for detection of Map in cattle.