Bulk Milk Testing Johne’s Disease Johne’s disease (JD), also known as paratuberculosis, is a contagious, chronic and debilitating cattle disease that has no cure. Contagious Mastitis Mastitis is characterized by inflammation of the mammary gland, usually caused by a bacterial infection, which leads to abnormal milk and decreased milk yield. Salmonella Dublin Salmonella Dublin are cattle-adapted bacteria that usually present as a respiratory illness in infected animals, particularly in young stock. Bovine Leukosis Leukosis is caused by the bovine leukemia virus (BLV). Five percent of cows will develop clinical disease with most being asymptomatic.