Direct and indirect effects of Johne's disease on farm and animal productivity in an Irish dairy herd

Johne's disease (JD), also called paratuberculosis, is caused by infection with the organism Mycobacterium avium spp. paratuberculosis (MAP), leading to chronic diarrhoea and ill thrift in adult cattle [6]. Typically, animals are infected as calves, but do not present with clinical signs until much later in life. Studies on JD are difficult due to long incubation period, complex exposure factors and poor test sensitivity associated with this disease [7,15,10]. Johne's disease is considered to adversely affect farm performance and as a result, economic profit. Currently, little data are available about the impact of JD on farm production in Ireland. Based on international studies, JD infection is associated with reduced milk production [15], increased involuntary culling rates [19] and increased calving interval and infertility [14,20]. Concern has been raised over potential links between Johne's disease in cattle and Crohn's disease in humans, which may lead to international barriers to trade in milk and milk products, including infant formula. This is of particular relevance to Ireland, noting concerns about MAP in raw milk [18], and the significant share (15%) Ireland has in the world powdered infant formula market [1]. This paper aims to describe the impact of JD on an Irish commercial dairy herd, and the effect of animal JD status on several measures of production. The history of the JD outbreak on this farm, including its impact on farm income, has been documented previously [3]. Farm performance prior to the disease outbreak was in the upper quartile of its peer group of milk monitored herds.This retrospective case study was undertaken on a single commercial dairy herd (the 'case herd') located in the province of Munster in Ireland. The case study is an investigation of the effect of Johne's disease on production in the herd confirmed. The Munster region in the south west of Ireland is the country's premier dairy area: in 2006, 61% of dairy calves in Ireland w