Abstract

Johne`s disease, caused by Mycobacterium avium subsp paratuberculosis (M. ptb), has emerged as a significant cause of losses on deer farms in New Zealand. It causes outbreaks of fatal clinical disease in young deer eight to 15 months of age, sporadic deaths in adults and production losses due to poor growth rates in yearlings, reduced calving percentages in hinds, reduced velvet production in stags, interference with tuberculosis testing and tuberculosis-like lesions in gut lymph nodes at slaughter. Although bovine and ovine strains have been isolated from deer, the bovine strain is more pathogenic and is responsible for the outbreaks of serious disease in young deer. Clinical disease results from heavy early challenge of young deer with the bovine strain. Mature animals are relatively resistant to infection. Calves are generally infected via the oral route from contaminated pasture and water. Intrauterine transmission to the foetus occurs commonly in clinically and subclinically infected hinds and infected milk may also play a role in transmission. Deer-to-deer transmission appears the most common route, although cattle-to-deer and sheep-to-deer transmission may occur. The role of wildlife is not known. Resistance to Johne`s disease has a genetic component, which appears to be related to resistance to bovine tuberculosis.

CG, Mackintosh

Proceedings of the New Zealand Society of Animal Production, Volume 68, Brisbane, Australia, 117-121, 2008