Johne's Disease

Johne's disease is a chronic, incurable bacterial infection affecting the intestines of cattle, sheep, goats and other ruminants. It's a significant cause of production loss and, because infected animals can silently spread the disease for years before showing signs, it requires a proactive, herd-level approach to control.

What causes it?

Johne's disease is caused by Mycobacterium avium subspecies paratuberculosis (MAP), a hardy bacterium that can survive in the environment (soil, water, slurry) for many months.

How it spreads

  • Most commonly, calves and lambs are infected in the first weeks of life, through ingestion of infected faeces, contaminated colostrum or milk.

  • Infection can also occur in the womb, from an infected dam.

  • Adult animals are generally more resistant to new infection, which is why control focuses heavily on protecting young stock.

  • The long incubation period — often 2 years or more — means infected animals can shed bacteria and spread disease well before showing any signs themselves.

Signs of disease

  • Chronic, progressive weight loss despite a normal appetite

  • Persistent diarrhoea, particularly in cattle (less consistently seen in sheep and goats)

  • Reduced milk yield

  • General poor condition and reduced fertility

  • Signs typically appear in adult animals (often 2–5 years old), even though infection occurred much earlier in life

Many more animals in a herd or flock are typically infected than are showing visible signs at any one time, which is why testing plays such an important role.

Diagnosis

  • Blood testing (ELISA) for antibodies — widely used but with limited sensitivity, particularly in early infection.

  • Faecal testing (culture or PCR) to detect shedding of the bacteria.

  • Milk testing, in dairy herds, as part of routine screening.

  • Because no single test is perfect, a herd-level testing strategy over time is generally more informative than a single snapshot test.

Control and management

Since there's no cure, control focuses on reducing spread and gradually lowering prevalence within the herd or flock:

  • Testing and culling persistently positive, high-risk animals

  • Snatch calving and clean colostrum management in high-risk herds, to reduce transmission from dam to offspring

  • Good hygiene around calving/lambing areas, feed and water troughs

  • Avoiding manure contamination of pasture, feed and water sources

  • Careful sourcing of replacement stock, ideally from herds/flocks of known low Johne's risk

  • Participation in industry schemes such as CHeCS-accredited Johne's control programmes, where appropriate for your enterprise

Why control matters

  • Beyond the direct production losses, Johne's status can affect herd accreditation, milk buyer requirements, and the ability to sell breeding stock.

  • There is ongoing scientific interest in a possible, though unproven, link between MAP and Crohn's disease in humans — while not established, it's a reason some supply chains have increased focus on Johne's control.

Still have questions?

If you'd like to discuss a testing strategy or Johne's control plan for your herd or flock, please contact us on 01797 252321.