Bovine Tuberculosis in Cattle: Respiratory Signs, Testing, and Herd Risk

Bovine tuberculosis, often called bTB, is a chronic infectious disease caused by Mycobacterium bovis. It most often affects cattle, but it can also infect other mammals, including deer, goats, dogs, and people. In the United States, it is considered a reportable disease, so a suspected or confirmed case involves regulatory follow-up in addition to veterinary care.

This disease usually develops slowly. Some cattle never show clear outward signs until infection is advanced, which is one reason herd testing and slaughter surveillance remain so important. When illness becomes visible, the lungs and nearby lymph nodes are common sites of disease, so respiratory signs may be part of the picture.

For cattle operations, bTB is not only an animal health issue. It can also affect herd movement, sale plans, culling decisions, milk safety discussions, and wildlife biosecurity. If your herd has a suspect animal, your vet can help you understand both the medical side and the regulatory steps that may follow.

Bovine tuberculosis is caused by the bacterium Mycobacterium bovis. It spreads most commonly through respiratory secretions, especially when cattle have close, repeated contact in enclosed or crowded settings. Infection can also occur through ingestion of contaminated feed or milk, and in some situations through contact with infected tissues.

Herd risk rises when cattle are introduced from unknown or higher-risk sources, when biosecurity is inconsistent, or when wildlife reservoirs are present nearby. In some regions, infected wildlife can help maintain the organism in the environment and contribute to re-exposure of livestock.

Because this disease can affect people, raw milk and unprotected exposure to respiratory secretions or infected tissues are important safety concerns. Pasteurization has greatly reduced human risk from milk, but suspected cases still require careful coordination with your vet and animal health officials.

Diagnosis usually begins with an official live-animal screening test, most often the caudal fold test (CFT) in cattle. If an animal is classified as a suspect on screening, follow-up may include the comparative cervical test (CCT), an interferon-gamma assay, or direct movement to slaughter under permit, depending on the case and regulatory plan.

Your vet may also recommend a broader herd review that looks at animal movement history, source herds, contact with wildlife, and any chronic respiratory or weight-loss cases in the group. In practice, diagnosis is not based on cough alone. Clinical signs can overlap with other conditions, so testing and herd context matter.

Definitive confirmation generally relies on postmortem findings and laboratory testing, such as culture and related regulatory lab methods on affected tissues or lymph nodes. If bTB is confirmed, herd management may include trace investigations, additional testing, movement restrictions, and a test-and-remove or depopulation plan directed by animal health authorities.

Prevention starts with biosecurity and herd sourcing. Work with your vet to review the health status of purchased cattle, quarantine additions when possible, and keep clear movement and testing records. Avoid mixing groups unnecessarily, especially if you do not know the source-herd history.

Reducing close contact between cattle and wildlife can also matter, particularly in areas where wildlife reservoirs are a concern. Protect feed and water sources, maintain fencing, and limit situations that encourage wildlife access to cattle areas.

Routine observation still matters, even though many infected cattle look normal at first. Chronic cough, weight loss, enlarged lymph nodes, or unexplained decline in production should prompt a veterinary conversation. Because bTB is zoonotic, milk safety and worker protection are part of prevention too. Pasteurization, careful tissue handling, and prompt reporting of suspect cases help protect both herd and human health.