Bovine Pulmonary Hypertension
Pulmonary hypertension, more commonly known as “high altitude disease” or “brisket disease,” is a result of decreased oxygen supply to the lungs for a significant amount of time. When lungs are not able to oxygenate due to low atmospheric oxygen tension, blood vessels throughout the organ constrict and remodeling of lung tissue occurs. The wall thickness of pulmonary arteries has been correlated with mean pulmonary arterial pressure (mPAP) due to increased resistance of blood flow within constricted vessels. Brief episodes of hypoxia can allow the pulmonary vessels to relax and return the mPAP to a normal state. However, a “chronic” state of hypoxia can be even as small as seven days consecutively.
As the pulmonary vessels thicken and narrow under low ambient oxygen levels, the muscle wall of the right heart also adapts to pressure changes by thickening its mass. Heart failure ensues when the inner chamber of the heart begins to dilate and attempts to allow for more blood accumulation and adequate outflow with each pump sequence, or heartbeat.
Signs of pulmonary hypertension can be mild and easy to miss. Although swelling of the brisket is commonly noted, this clinical sign does not have to be present. Affected animals may also demonstrate clinical signs similar to typical pneumonia such as rapid respiratory rate with increased effort, coughing, and breathing with the mouth open. Additional caution should be noted by managers observing these symptoms in cattle during warmer months when pneumonia may be the less likely of two diagnoses.
Calves are more likely to suffer from cardiopulmonary insufficiency because their organ systems are not fully developed until they are yearlings. It is also important to note that the lung surface area of cattle is rather small in comparison to other animals of the same size. This is another reason that diseases like pneumonia are a great concern in cattle.
Some cattle are predisposed to this condition due to genetics. At altitudes over 7,000 thousand feet these cattle develop severe pulmonary hypertension and right heart failure. Affected animals develop subcutaneous fluid accumulation in the brisket region. Research notes from Colorado State University have identified a 2 to 10 percent incidence of disease in cattle herds living in altitudes over 8,000 feet.
It is interesting to note that llamas are not as affected by decreased oxygen levels at high altitudes because they have adapted better to living in mountain regions.
Testing is possible to identify cattle with high mPAP and in order to organize herd management. Pulmonary pressure gradients are known to be a fairly heritable trait in cattle. Geneticists advise herd owners in high altitude environments to breed bulls that allow for decrease of hypertensive offspring.
High mPAP cattle are those testing greater than 45mmHg, typically. The test is utilized primarily for screening purposes as the failure rate can actually increase along with the corresponding altitude. This means that a value obtained at 5,000 feet does not necessarily predict the animal’s pulmonary response at 8,000 feet. Testing mPAP can often identify affected herds that were not suspected of having altitude disease. Reports have been noted from Nebraska and Texas ranches, as well. — Dr. Genevieve Grammer is a veterinarian working out of the Pikes Peak region. Please address correspondence to drgigi19@ gmail.com