Herd management practices and the transmission of Johne's disease within infected dairy herds in Victoria, Australia.

A retrospective cohort study involving 137 dairy herds randomly selected from all 390 participating in the Victorian Test and Control Program for bovine Johne's disease was undertaken to gain insight into the relationships between calf rearing practices and the occurrence of bovine Johne's disease on infected dairy farms. Each study farm was visited between July 2005 and January 2006 and a structured survey examining herd management and calf rearing practices was completed. The resultant data, along with information from annual herd testing for Johne's disease and records of clinical Johne's disease diagnosed in the herd, from May 1990 to March 2008, were analysed. Factors associated with time to the birth of the animal that was the first home-bred clinical case of Johne's disease or ELISA positive animal born after the second annual whole herd test in the herd were investigated using survival analysis methods. The publicly-subsidised Test and Control Program commenced in 1996. On the 1st of July 2003 the program was modified with more rigorous and externally audited calf rearing requirements introduced for all participants. The more stringent calf rearing requirements introduced in July 2003 appear to have translated into significantly reduced disease transmission within the infected study herds. Copyright (c) 2010 Elsevier B.V. All rights reserved.