Johne's disease (paratuberculosis), caused by Mycobacterium avium subspecies paratuberculosis (MAP), is a chronic, progressive, and ultimately fatal granulomatous enteritis affecting ruminants, particularly dairy cattle. The disease poses significant welfare challenges and substantial economic losses to the livestock industry.
MAP infection typically occurs in calves under 6 months old, but clinical signs usually manifest years later. The disease progresses through subclinical and clinical phases. Clinical Johne's disease causes profuse watery diarrhoea, severe weight loss despite maintained appetite (the animal appears to eat normally but cannot absorb nutrients), hypoproteinaemia causing submandibular oedema (bottle jaw), progressive debilitation, and eventual death. Welfare impacts include chronic pain, weakness, reduced mobility, and progressive deterioration in quality of life over months.
Diagnosis is complicated by the long incubation period (often 2-10 years), the insensitivity of early-stage tests, and intermittent shedding of MAP in faeces. Available tests include ELISA serology, faecal PCR or culture, and post-mortem histopathology. Herd-level management requires a testing programme combined with interpretation of results in context of clinical signs.
No cure exists for Johne's disease, making prevention critical. Control programmes focus on hygiene measures to prevent calf exposure to adult faeces, identifying and culling high-risk animals, and testing protocols. The clean-calf rearing programme—separating calves at birth, feeding colostrum from test-negative cows, and avoiding pooled milk—is fundamental to breaking the transmission cycle.
Vaccination reduces clinical disease expression and MAP shedding but does not prevent infection. In high-prevalence herds, vaccination as part of a control programme can improve welfare outcomes by reducing the proportion of animals that develop clinical disease.
Early identification and culling of animals showing clinical signs is important for individual welfare and herd health. Animals with advanced Johne's disease have a poor prognosis and continuing to maintain them until slaughter-weight may compromise welfare. Farmers should work with vets to establish humane endpoints and culling policies that balance economic considerations with animal welfare obligations.
Johne's disease management should form part of an integrated herd health plan, with clear monitoring, testing, and response protocols agreed with the attending veterinarian. Regular review of the herd's disease status enables targeted interventions to reduce the welfare burden of this progressive and debilitating condition.