Introduction: High mountain disease is a non-infectious disease also known as brisket disease, high altitude disease, or pulmonary hypertensive heart disease. Like its name implies, most affected animals have been on range at elevations of 6,000 feet or higher. The disease can develop in animals of all ages and in most breeds of cattle; however, it seems to be more common in steer calves less than a year old. Native cattle are less likely to develop high mountain disease than cattle recently introduced to the higher altitude.
Causative Agent: The high-altitude environment exposes the cattle to low levels of oxygen. This results in pulmonary vasoconstriction, hypertension and ultimately congestive heart failure. Many factors can combine to increase the chances an animal will have problems at high altitudes. These factors include genetic weakness, pneumonia, plant poisoning (such as locoweed), lungworm infection, sub-zero weather, chronic pulmonary lesions, or a ruptured diaphragm. These problems can accompany or trigger the onset of the disease.
Clinical Signs: The animal is first noted to be lethargic (depressed), usually after a period of severe cold or other stress. Subcutaneous edema (fluid build-up under the skin) may then develop in the brisket region and extend into the head and abdominal wall. Sometimes, the animal appears emaciated (extremely thin) instead of swollen. The jugular vein is distended and pulsates. Watery diarrhea may develop. The animal has a hard time breathing, can be reluctant to move, and may collapse and die if forced to exert itself.
A necropsy of an animal with high mountain disease can show pockets of serous fluid between the internal organs, and lesions on the liver and the lungs. The pulmonary arteries may be full of thrombi (blood clots) and there is a generalized swelling in many portions of the body. In the severe cases, the heart shows evidence of right ventricular hypertrophy (enlargement), and can have a rounded contour.
Treatment: The most obvious and immediate treatment is to move the animals to a lower elevation; however, this should be done in a way that causes as little stress as possible. Some animals will recover without help. Others will need supportive therapy, including antibiotics to combat pneumonia. The use of oxygen and heart medications may be considered for valuable animals. Because the disease will most likely recur, any previously affected animals should not be returned to higher altitudes.
Prevention: One of the best ways to prevent this problem is to select for animals that seem to be genetically resistant to high mountain disease. These animals should be used for replacements. It is also important to remove or limit exposure to as many toxic plants (particularly locoweed) as possible. Lastly, it is important to allow animals to adapt to the high altitudes slowly. Sudden changes in altitude should be avoided.