New Zealand boasts a population of approximately one million European red deer (Cervus elaphus) farmed commercially for venison and for velvet, a farming practice which is not commonly employed internationally.

Johne’s disease, caused by infection with Mycobacterium avium subsp. paratuberculosis (MAP), was first diagnosed in farmed deer in NZ in 1979 is recognised as a production limiting disease of concern to the NZ deer farming industry with some estimates of herd prevalence as high as 63%. This chronic and contagious bacterial infection often manifests in deer as a more acute infection than is seen in other species, with progression from infection through to clinical disease or death often occurring more rapidly than in cattle or sheep and with some particularly susceptible animals dying from the disease as early as eight months of age.

As with sheep and cattle, young deer typically become infected following oral ingestion of pasture and/or water contaminated with faecal matter. As with other species, indictors of MAP infection may include decreased weight gain and ill-thrift which is often, but certainly not always, accompanied by scouring (diarrhoea). As these signs are also common to a variety of other causes, the only way to know for sure is through laboratory testing.