Ovine Johne's disease (OJD, caused by Mycobacterium avium paratuberculosis) is a chronic wasting disease in sheep causing progressive malnutrition and death. Vaccination and biosecurity can control but not eliminate it.
OJD causes a slow, progressive, and uncomfortable death from malnutrition and protein loss. Affected sheep lose body condition over weeks to months, experiencing increasing weakness, lethargy, and eventually the discomfort of severe cachexia. Bottle-jaw from protein deficiency is visible but the internal suffering from intestinal disease is less visible and may be overlooked or misattributed in production contexts. The welfare challenge is the long subclinical phase during which sheep are infected and shedding but appear normal - making flock management decisions based on visible welfare difficult. The welfare case for vaccination is strong: it reduces both clinical disease in individual animals and flock-level infection pressure, decreasing the total burden of suffering even though it does not achieve eradication. Prompt culling of clinical cases reduces prolonged suffering.