There is a lot of information that shows a relationship between the bacterium that causes Johne's Disease and Crones but none of it is conclusive. New information that shows that some outside immune stimulus (like infecting patients with Trichuris spp. intestinal parasites) is also showing that there is a significant immune componet to the disease. Some cattle dewormers, levamisole, have been used in the past and shown some improvement along with the sulfasalazine treatments.
Having also been a dairy inspector, I know that Mycobacterium can escape the pasteurization process. HTST and slow Vat process products are routinely cultured for contaminants and the dairies are notified accordingly. UHP processes are more efficient IMHO.