Pulmonary Hypertension in Sheep: Heart-Lung Circulation Problems

Pulmonary hypertension is high pressure inside the blood vessels that carry blood from the heart to the lungs. In a sheep, that extra pressure forces the right side of the heart to work harder every time it pumps. Over time, the heart muscle can enlarge, weaken, and eventually struggle to keep up.

This is usually not a stand-alone disease. More often, it is a consequence of another problem that lowers oxygen levels or damages the lungs, such as chronic pneumonia, lung tumors like ovine pulmonary adenocarcinoma, long-term inflammatory lung disease, or environmental stressors that reduce normal oxygen exchange. High altitude can also contribute because lower oxygen levels trigger narrowing of the lung blood vessels.

For pet parents and flock managers, the practical concern is that sheep often hide illness until breathing becomes noticeably harder. By the time signs are obvious, the sheep may already have significant strain on both the lungs and the right side of the heart. Early veterinary evaluation gives your vet more options and may help identify whether the underlying problem is treatable.

In sheep, pulmonary hypertension is usually secondary, meaning another disease or stressor raises pressure in the lung circulation. A common pathway is chronic low oxygen. When oxygen levels stay low, the small arteries in the lungs constrict. Over time, those vessels can thicken and narrow further, which increases resistance to blood flow and strains the right ventricle.

Important triggers include chronic or severe pneumonia, recurrent respiratory infections, poor ventilation, crowding, transport stress, and lung conditions that reduce normal gas exchange. Ovine pulmonary adenocarcinoma can also cause progressive breathing difficulty and poor thrift in adult sheep. In some cases, toxins or chronic heart disease may contribute, though these are less common than respiratory causes.

High altitude is another recognized risk because lower environmental oxygen can trigger pulmonary arterial constriction. This process is well described in cattle with brisket disease and is biologically relevant to other ruminants exposed to sustained hypoxia. Sheep living or grazing at elevation, especially if they also have underlying lung disease, may be at greater risk.

Because the condition often reflects a deeper problem, your vet will usually focus on identifying the primary cause rather than treating the elevated lung pressure alone.

Diagnosis starts with a careful history and physical exam. Your vet will ask about altitude, recent transport, pneumonia in the flock, weight loss, exercise intolerance, and whether the sheep has swelling under the jaw or brisket. On exam, your vet may hear abnormal lung sounds, note increased breathing effort, or detect signs consistent with right-sided heart strain.

Basic testing may include bloodwork, pulse oximetry if available, and thoracic imaging. Chest ultrasound can help identify pleural fluid, superficial lung consolidation, or masses. Radiographs may be used in some hospital settings, though they are less practical on many farms. Echocardiography is the most useful way to assess the right side of the heart and estimate pressure-related changes in the pulmonary circulation when referral care is available.

Your vet may also work through likely underlying causes. That can include testing or herd-level assessment for bacterial pneumonia, chronic viral-associated lung disease, or ovine pulmonary adenocarcinoma. In advanced or fatal cases, necropsy may be the clearest way to confirm the diagnosis and protect the rest of the flock by identifying the root problem.

Because pulmonary hypertension in sheep is often a syndrome rather than a single disease, diagnosis is usually a combination of clinical signs, evidence of cardiopulmonary strain, and ruling in or out the conditions that commonly cause chronic hypoxia.

Prevention focuses on reducing the lung and oxygen stresses that can lead to elevated pressure in the pulmonary circulation. Good ventilation, lower dust exposure, avoiding overcrowding, and minimizing transport and weather stress all support healthier lungs. Prompt treatment of pneumonia matters, because chronic or repeated respiratory disease can leave lasting damage that increases strain on the heart.

Biosecurity is also important. New sheep should be introduced carefully, and chronic weight loss or progressive breathing difficulty should never be ignored. Conditions such as ovine pulmonary adenocarcinoma can spread within a flock and may look like a routine respiratory problem at first.

If your flock lives at higher elevation, talk with your vet about whether altitude may be contributing to poor performance or breathing issues. In some situations, moving affected animals to lower elevation can reduce hypoxic stress. Your vet can also help review housing, nutrition, parasite control, and vaccination planning to lower the overall burden of respiratory disease.

The key point is that pulmonary hypertension is often preventable only indirectly. Protecting lung health early gives your sheep the best chance of avoiding long-term heart-lung circulation problems.