Johne's disease — known clinically as paratuberculosis — is one of the most insidious and economically destructive livestock diseases in Australia. Caused by the bacterium Mycobacterium avium subspecies paratuberculosis (MAP), Johne's disease is a chronic, progressive infection of the gastrointestinal tract that affects cattle, sheep, goats, and deer. There is no cure. There is no practical treatment. And perhaps most frustratingly, infected animals can shed the bacteria silently into the environment for months or years before showing any clinical signs — all the while contaminating pastures, water sources, and new animals entering the property.

For Australian livestock producers, Johne's disease is not a theoretical concern. It is estimated to cost the Australian cattle industry alone over $40 million annually in production losses, premature culling, and market access restrictions. In sheep, ovine Johne's disease (OJD) is widespread in the high-rainfall zones of south-eastern Australia, and in goat operations caprine Johne's disease (CJD) is an increasingly recognised and under-controlled threat. Understanding how the disease works, how to detect it, and how to manage it on your property is one of the most important investments you can make in the long-term viability of your livestock enterprise.

What Causes Johne's Disease?

The causative agent, MAP, is a slow-growing mycobacterium closely related to the bacteria responsible for tuberculosis and leprosy in humans. Unlike most bacterial infections, MAP is extraordinarily hardy in the environment — it can survive in soil, water, and on pasture for months to years, depending on temperature and UV exposure. Acid soils, shaded areas, and waterlogged ground are particularly favourable to MAP survival, making many Australian high-rainfall farming regions ideal conditions for the bacteria to persist.

Infection almost always occurs in very young animals — typically calves, lambs, or kids under 6 months of age. The young gut is uniquely susceptible to MAP colonisation because the immune response is not yet fully developed. In adult animals, the dose required for infection is substantially higher and the gut far more resistant, which is why management strategies focus heavily on preventing exposure of neonates rather than attempting to protect mature stock.

Once MAP enters the wall of the small intestine, it is taken up by immune cells and establishes a persistent, slow infection. The body's immune response gradually damages the intestinal lining, impairing the gut's ability to absorb nutrients and fluids. This process unfolds over months to years, which is why Johne's disease has an incubation period of 2 to 5 years in cattle and 2 to 4 years in sheep and goats before clinical signs emerge.

How Johne's Disease Spreads

Understanding transmission routes is fundamental to controlling Johne's disease on a property. MAP is shed in the faeces of infected animals and, at high levels of infection, in colostrum and milk. The primary routes of transmission are:

  • Faecal-oral transmission: The most common route. Newborn animals ingest MAP-contaminated faeces, pasture, water, or bedding. Even trace contamination of the neonatal environment is sufficient to establish infection in a susceptible young animal.
  • Contaminated colostrum and milk: Cows, ewes, and does with high bacterial loads can shed MAP in colostrum and milk, directly infecting their own offspring before they ever reach pasture.
  • In-utero transmission: Less common but documented, particularly in cattle with advanced infection. Calves born to cows in the late subclinical or clinical stages of Johne's disease may be infected before birth.
  • Contaminated pasture: Pasture grazed by infected animals accumulates MAP over time. The concentration is highest around areas of high faecal density — laneways, water troughs, shade trees, and yards. Once a pasture is heavily contaminated, the infection risk for young animals persists for years.

New introductions of infected animals are the single most common way Johne's disease enters a previously clean property. An animal purchased from an infected property, even if it appears completely healthy at the time of purchase, may be silently shedding MAP at low levels. This is why biosecurity around livestock introductions is the foundation of Johne's disease prevention.

Symptoms of Johne's Disease

The clinical presentation of Johne's disease differs slightly between species, but the underlying mechanism — progressive protein-losing enteropathy from gut damage — is the same across all affected livestock.

Johne's Disease Symptoms in Cattle

Clinical signs in cattle typically emerge in animals aged 3 to 5 years, though occasionally younger animals are affected. The most characteristic signs are:

  • Profuse, watery diarrhoea that is persistent and does not respond to treatment. Unlike many other causes of diarrhoea, the faeces are characteristically liquid and may have a greenish tinge, without blood or mucus in most cases.
  • Progressive weight loss despite normal or even increased appetite. The animal continues to eat but cannot absorb nutrients effectively through the damaged gut.
  • "Bottle jaw" (submandibular oedema) — a soft, fluctuant swelling under the jaw caused by low blood protein levels (hypoalbuminaemia) resulting from protein loss through the gut.
  • Dull, rough coat and general unthriftiness as the disease progresses.
  • Death in the terminal stage, usually from dehydration, protein deficiency, and secondary complications.

An important feature of bovine Johne's disease is that affected animals rarely have a fever. The absence of fever in a thin, scouring cow or steer is a significant clinical indicator that should raise suspicion of Johne's disease rather than an acute infectious cause.

Johne's Disease Symptoms in Sheep (OJD)

Ovine Johne's disease presents differently from the bovine form. Persistent diarrhoea is rare in sheep with OJD — the gut architecture is different and fluid loss is less dramatic. The primary signs in sheep are:

  • Progressive weight loss and muscle wasting, particularly over the back and hindquarters (sometimes described as "knife-edge" along the spine)
  • Reduced fleece weight and wool break in affected animals
  • "Bottle jaw" (submandibular oedema) in animals with advanced disease and very low protein levels
  • Separation from the mob and general dullness
  • Sudden death in animals that appeared only moderately affected, often following a period of stress such as yarding or transport

Because ill-thrift and weight loss in sheep have many potential causes, OJD can easily be attributed to worms, poor nutrition, or other conditions. This contributes to the disease being significantly under-diagnosed in Australian sheep flocks, particularly in early outbreak stages when only a small proportion of animals are clinically affected.

Johne's Disease Symptoms in Goats (CJD)

Caprine Johne's disease more closely resembles the bovine presentation than the ovine one. Goats with CJD typically show:

  • Progressive weight loss
  • Intermittent to persistent diarrhoea or softened faeces
  • Bottle jaw in advanced cases
  • Reduced milk production in dairy animals

Goats are also susceptible to infection from cattle-strain MAP, unlike sheep, which primarily carry sheep-strain MAP. This cross-species susceptibility is particularly relevant for mixed cattle-and-goat properties where biosecurity management must account for both strains.

The Subclinical Iceberg

One of the most challenging aspects of managing Johne's disease is that for every animal showing clinical signs, there are typically 10 to 25 more animals in the same herd or flock that are infected but showing no visible signs. These subclinically infected animals are often shedding MAP at varying levels, infecting their environment and their offspring, while appearing to be completely healthy. In early-outbreak scenarios, the clinical cases you can see represent only the tip of a much larger infection iceberg within the mob.

This subclinical burden is what makes flock or herd-level testing — rather than simply identifying and culling clinical cases — the cornerstone of an effective Johne's disease control program.

Diagnosing and Testing for Johne's Disease

Several diagnostic tests are available for Johne's disease in Australia, each with different performance characteristics and appropriate uses. Understanding the limitations of each test is important for interpreting results correctly.

ELISA Blood Test (Serology)

The ELISA (enzyme-linked immunosorbent assay) blood test detects antibodies to MAP in blood serum. It is widely used for herd and flock-level testing in Australia because it is inexpensive and allows large numbers of animals to be tested simultaneously. Key characteristics:

  • Good specificity (few false positives) in cattle with moderate to high infection levels
  • Low sensitivity in early infection — animals infected for less than 2 years often test negative despite being infected (false negatives are common)
  • Most useful for herd prevalence estimation and annual monitoring programs
  • A negative herd test result on ELISA does not certify freedom from Johne's disease

Faecal Culture

Faecal culture grows MAP from faeces samples and is considered a highly specific test — a positive result is essentially diagnostic. However, it is slow (results take 8 to 16 weeks due to MAP's extremely slow growth rate) and expensive, and sensitivity is reduced in early-stage animals shedding at low levels. Most useful for confirming suspect clinical cases.

PCR Faecal Testing

Polymerase chain reaction (PCR) directly detects MAP DNA in faeces. PCR is faster than culture (days rather than weeks) and increasingly affordable. It is more sensitive than culture in high-shedding animals but less reliable in animals with low faecal shedding. Pooled faecal PCR (combining samples from multiple animals) is a cost-effective approach for herd-level surveillance.

Post-Mortem Diagnosis

For animals that die or are euthanased, post-mortem examination of the intestinal tract by a veterinary pathologist remains one of the most reliable diagnostic approaches. The characteristic gross and histological changes to the intestinal wall — along with culture or PCR of intestinal tissue — provide definitive confirmation. If a clinical Johne's disease suspect dies on your property, submitting the carcass or samples to a veterinary diagnostic laboratory provides both a confirmed diagnosis and valuable information about your property's infection status.

Johne's Disease Accreditation and Market Access

Australia operates national Johne's disease management programs under the umbrella of the Johne's Disease Market Assurance Programs (JD MAP) and the National Johne's Disease Control Program (NJDCP). These programs provide accreditation levels that affect livestock market access, particularly for sale of cattle and sheep to other properties or export-eligible markets.

For cattle, the Cattle Johne's Disease Management Plans (CJDMP) operate at the state level, with properties assigned management categories based on risk status and testing history. Higher accreditation levels provide better market access. For sheep, the OJD Management Program (OJD MP) provides a similar tiered accreditation system relevant across NSW, VIC, SA, WA, and Tasmania.

The practical implication for livestock buyers: always ask for Johne's disease status before purchasing animals. Buying from properties with no known testing history or from regions with high OJD prevalence (such as the high-rainfall slopes and tablelands of NSW and Victoria) without appropriate testing represents a genuine biosecurity risk to your own property.

Vaccination for Johne's Disease

The only commercially available Johne's disease vaccine currently registered in Australia is Gudair, which is approved for sheep and goats. Gudair is a killed-bacteria vaccine that significantly reduces the level of MAP shedding in vaccinated animals and markedly reduces the proportion of the flock developing clinical disease. It does not prevent infection entirely, but it substantially reduces the rate at which MAP spreads through a flock and the number of animals that progress to clinical disease.

Key points about Gudair vaccination:

  • Must be given to lambs or kids before 16 weeks of age for full efficacy; given as a single subcutaneous injection
  • Requires a vaccination record as Gudair-vaccinated animals cannot subsequently be tested with serological ELISA tests — the vaccination itself triggers a positive antibody result that cannot be distinguished from true infection
  • Restricted to use in properties with a registered OJD management plan in some states — contact your state agriculture department for current requirements
  • No approved cattle vaccine is currently available in Australia; control in cattle relies on biosecurity, culling, and management practices rather than vaccination

Management and Control on Infected Properties

Once Johne's disease is confirmed on a property, complete eradication is rarely achievable. The realistic goal is to reduce the within-flock or within-herd prevalence over time, minimise environmental contamination, and limit production losses. The core management principles are:

  • Cull clinical cases promptly. Animals with advanced clinical signs are the highest shedders of MAP and should not remain in the flock. Rapid culling of confirmed or strongly suspected cases reduces the environmental contamination load.
  • Minimise neonatal exposure. Remove calves, lambs, or kids from contaminated paddocks as early as practically possible. Avoid yarding or concentrating young animals in areas of high faecal density. In dairy operations, pasteurisation of colostrum before feeding significantly reduces early-life MAP exposure.
  • Implement Gudair vaccination in sheep and goat flocks. This is the most cost-effective single intervention in sheep Johne's disease management and should be considered on any property with confirmed OJD or in high-risk regions.
  • Spell heavily contaminated paddocks. Paddocks used for calving, lambing, or kidding on infected properties accumulate high MAP loads. Spelling these paddocks for 12 months or longer — particularly over summer when UV and heat accelerate bacterial death — reduces reinfection risk for subsequent years' young stock.
  • Don't buy in risk. Only purchase replacement animals from properties with known, documented Johne's disease status. Quarantine and test all introductions before adding them to your main mob.
  • Annual testing and monitoring. Work with your vet or livestock health officer to establish an annual testing protocol appropriate to your species, accreditation level, and risk status. Tracking herd or flock prevalence over time tells you whether your management is actually reducing the infection burden.

Economic Impact

The economic cost of Johne's disease on an infected property is often greater than it appears, because so much of the damage occurs in subclinically affected animals that go unrecognised. Documented losses include reduced weight gains in growing animals, reduced reproductive performance in breeding females, premature culling costs, reduced market access for livestock sales, increased feed costs per unit of production, and the direct costs of testing, vaccination, and veterinary consultation. On properties where Johne's disease is uncontrolled and prevalence is high, total losses can reach several hundred dollars per breeding female per year.

The investment in a structured Johne's disease management program — accreditation, annual testing, vaccination where appropriate, and rigorous biosecurity on introductions — consistently returns more than its cost on infected properties, and prevents the far greater cost of introducing the disease to a clean one.

This guide is for general information purposes. Johne's disease management programs are regulated at the state level in Australia and requirements vary. Contact your state department of agriculture or an accredited veterinarian for a management plan appropriate to your property, species, and region.

For more, see our Footrot in Livestock: Symptoms, Treatment & Paddock Management and Paterson's Curse: What Australian Livestock Producers Need to Know.