Bovine High-Mountain Disease in Cows

Bovine high-mountain disease (BHMD) is a heart and lung condition seen in cattle living or grazing at higher elevations. You may also hear your vet call it brisket disease or hypoxia-induced bovine pulmonary hypertension. At altitude, lower oxygen levels can cause the blood vessels in the lungs to constrict. Over time, that raises pressure in the pulmonary arteries and puts heavy strain on the right side of the heart.

As that strain worsens, some cattle develop right-sided heart failure. Fluid then leaks into dependent tissues, especially the brisket region, lower chest, ventral abdomen, and sometimes under the jaw. That visible swelling is often what pet parents or producers notice first, but the disease process starts earlier in the lungs and heart.

BHMD is most often discussed in cattle at elevations of 5,000 feet (1,524 m) or higher, and it has long been recognized in mountain herds in the western US. Some animals become sick within days to weeks after moving uphill, while others may live at altitude for much longer before showing signs. Susceptibility varies by genetics, age, management, and other health stressors, so not every cow in the same pasture is affected the same way.

The main driver of BHMD is low oxygen at altitude. In susceptible cattle, hypoxia causes the small arteries in the lungs to narrow. That raises pulmonary arterial pressure and forces the right ventricle to work harder to push blood through the lungs. Over time, the heart muscle enlarges, then may weaken and fail.

Altitude matters, but it is not the whole story. Cattle are considered especially susceptible to this response because of the structure of the bovine lung and pulmonary circulation. Genetics also play a major role. PAP measurements are heritable enough that breeding selection is a key prevention tool in mountain herds.

Other stressors can worsen risk or make disease show up sooner. Your vet may look for concurrent respiratory disease, heavy parasite burden, chronic cold stress, high nutritional push in some animals, congenital heart disease, or toxic plant exposure. Locoweed has been directly linked to development of congestive heart failure in susceptible cattle at elevation, so pasture history matters too.

BHMD can also be confused with other causes of swelling, respiratory distress, or poor performance. That is why a careful veterinary workup is important before making management decisions for the individual cow or the herd.

Diagnosis starts with a farm history and physical exam. Your vet will ask about elevation, recent movement from low to high altitude, timing of signs, pasture exposures, breeding history, and whether other cattle are affected. On exam, they may find brisket edema, jugular distension, abnormal lung sounds, increased breathing effort, or signs consistent with right-sided heart failure.

The most important confirmatory test is pulmonary arterial pressure (PAP) testing. This is done by passing a catheter through the jugular vein into the pulmonary artery to measure pressure directly. In cattle at about 5,000 to 7,000 feet, a normal mean PAP is typically around 34-41 mm Hg. A value over 50 mm Hg is considered high risk for BHMD and is especially important when making breeding and culling decisions.

Your vet may also recommend additional testing to rule out look-alike problems or contributing disease. Depending on the case, that can include CBC and chemistry testing, ultrasound to look for pleural or abdominal fluid, auscultation for murmurs, and evaluation for respiratory disease, parasitism, or congenital heart defects. In advanced cases, necropsy findings in animals that die can help confirm the diagnosis and guide herd prevention.

Timing matters with PAP testing. Cattle moved from low to high elevation generally need to remain at altitude for at least 3 weeks before testing gives the most useful information about adaptation risk.

Prevention focuses on herd selection and altitude management. The most effective long-term tool is PAP-based breeding selection. Cattle with elevated PAP, especially those over 50 mm Hg, are considered higher risk and generally should not be retained for breeding in high-altitude programs. Affected animals also should not be returned to mountain pastures after recovery, because recurrence can happen.

If cattle are moved from lower to higher elevation, work with your vet on a monitoring plan during the first several weeks. Clinical signs often appear within 3 to 4 weeks after the move, although they can occur sooner. Low-stress handling, good respiratory disease control, parasite management, and avoiding unnecessary physiologic stress can all help reduce the burden on the lungs and heart.

Pasture review matters too. If locoweed is present, ask your vet or extension team about forage management and safer grazing strategies. Concurrent respiratory disease and other causes of chronic low oxygen can worsen pulmonary hypertension, so prevention is not only about altitude. It is also about keeping the whole herd as healthy as possible.

For herds that live or summer at elevation every year, prevention is usually more practical than treatment. A proactive plan with your vet can include PAP testing of breeding candidates, culling decisions, movement timing, and investigation of any unexplained deaths before the next season.