Johne’s Disease: Testing, Culling, and Biosecurity

Johne's disease is a slow, chronic infection of the gut that causes weight loss and falling milk in adult cows. It is spread mostly to calves, long before any cow shows signs.

Key points

Johne's infects calves early and shows up in adults years later.
There is no cure, so prevention and culling decisions matter.
Calf management does most of the preventive work.
Test with a plan, using your vet's advice on methods and results.
Buy carefully and keep manure away from young stock.

What Johne's disease is

Johne's disease is caused by a bacterium that lives in the intestine. Infection almost always happens in young calves, but signs may not appear until the animal is an adult, often after several lactations.

Affected cows lose weight despite a good appetite, may have watery manure, and lose milk. There is no cure. That is why prevention and herd management are the focus.

Because the disease is slow, a herd can carry it for years before anyone notices. Many farms learn about it through thin cows that stop responding to normal care.

How it spreads

The organism passes in manure of infected cows, and also in colostrum and milk. Calves pick it up by swallowing it, from contaminated teats, bedding, feed, water or milk. Calves are most vulnerable in early life.

Many infected cows shed bacteria for a long time before they look sick, so a cow that appears normal can still be spreading it.

Testing options

Testing options include blood or milk tests, usually run through herd testing labs, and manure tests such as culture or DNA-based methods. Each has strengths and limits. Ask your vet which fits your goals and how to read a negative result, since a negative does not always mean a cow is free of infection.

Many states and programs have herd-level Johne's control programs with set procedures, risk assessments and sometimes testing support. Ask your vet and state animal health office what is available.

Your state animal health office may offer approved test procedures and cost-sharing. Check before you pay for testing on your own.

Herd risk assessment with your vet
Individual cow testing on a set schedule
Testing before purchase where possible
Keeping results by cow ID
Follow-up testing of positive and suspect cows

Culling and management decisions

Culling test-positive cows reduces the source of new infection, and many programs advise doing so, with timing based on the animal's value, test result and stage of lactation. This is a herd decision to make with your vet.

Until a positive cow leaves, keep her separate at calving, do not feed her colostrum or milk to calves and keep her manure away from young stock.

Calf-focused control

Because calves are most at risk, calf management does most of the preventive work. Calve cows in clean, dry, individual areas. Remove the calf from the cow quickly. Feed colostrum from a tested or low-risk source and use pasteurized milk or milk replacer.

Keep calf feeding equipment clean, avoid manure contact with feed and water, and house young calves apart from adult cows and their manure. Ask your vet how to set up this part of the program.

Clean, dry calving area
Separate calves quickly
Colostrum from low-risk cows
Pasteurized milk where possible
Calf housing away from adult manure

Biosecurity and buying cattle

Bringing in infected animals is a common way to introduce Johne's. Buy from herds with known test status, ask for records, and test where practical. Do not share manure-handling equipment between adult cow areas and calf areas.

Keep visitors, trailers and equipment from spreading manure from other farms into your calf and heifer areas.

Heifers raised on another farm or bought as calves should be treated as a risk until you know the herd of origin and its Johne's status.

Common mistakes

Common errors include testing without a plan for what to do with results, ignoring calf-area hygiene, feeding pooled colostrum from unknown cows, and waiting until cows look thin before taking action. Johne's is a long-term program. Improvement is measured over years, not months.

When to get help: Work with your vet and state animal health office on a herd plan, and call your vet for any cow with chronic weight loss and diarrhea. Follow label or vet-set milk and meat withdrawal times exactly for any treated animal.

Sources and further reading

Organization homepages are linked so you can search them for current guidance on this topic.

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