by Tina L. LaVallee

On Feb. 1, 2019, the American Angus Association made public the first set of research EPDs for pulmonary arterial pressure (PAP). The goal of this new EPD is to help producers select breeding stock that are less susceptible to High Altitude Disease, a potentially fatal condition affecting cattle exposed to elevations of 5,000 feet and above. The current research EPDs consist of A.I. permitted bulls with accuracy values of .40 or higher for trait, as determined through the combined databases of the American Angus Association, Colorado State University, Angus Genetics Inc. (AIG) and Dr. Tim Holt.

High Altitude Disease, also known as Brisket Disease, Bovine High Altitude Disease, and Dropsy, is caused by a lack of oxygen, which leads to increased pulmonary hypertension and terminates with congestive heart failure. The disease is very common in high altitude regions (over 5,000 feet) of Colorado, Wyoming, New Mexico, and Utah. High Altitude Disease can be triggered in susceptible animals by a number of factors, including environmental conditions, stress, overall health, and age. These factors can occur simultaneously in a perfect storm, killing the susceptible cattle within days or weeks after being moved to high altitudes. Colorado, where cattle are often grazed at altitudes of 9,000 to 12,000 feet, suffers the greatest economic impact of the disease and losses can exceed 5 percent in some herds. In addition, pulmonary hypertension has recently become a significant cause of death in feedlot cattle at lower elevations, spawning research to determine if a connection between the two diseases exists.

Identifying the cattle most likely to fail at high altitudes is crucial to profitable operations and a genetic link has long been suspected. This link was recently validated by the research of Dr. Tim Holt, Colorado State University associate professor of clinical sciences in the College of Veterinary Medicine and Biomedical Sciences. The emerging genetics coupled with the size of the cattle industry in the affected states prompted action from the American Angus Association. At the 2018 American Angus Convention, the disease was the subject of an innovation workshop conducted by Wyoming based Neogen territory manager Hannah Garrett. The workshop included a live-animal demonstration of a Pulmonary Artery Pressure (PAP) measurement, conducted by Dillon, MT veterinarian Ben Abbey. This eye-opening workshop was the first time many producers east of the Rockies had heard of High Altitude Disease or its potential impact on a national scale.

“Like all muscles, the heart remodels itself to accommodate additional stress caused by a low oxygen environment,” Garrett said. “In affected cattle, the heart stretches and thickens in an effort to keep the body oxygenated. These changes lead to a buildup of fluids and right ventricular heart failure. Producers send cattle up the mountain and some of them never return.”

The resulting edema often settles in the brisket area, causing the noticeable swelling that gives this condition its common name of Brisket Disease. Taking a PAP measurement at the desired high altitude can detect susceptibility by indicating the resistance to blood flow through the lungs. The PAP measurement is an invasive test that is very similar to cardiac cauterization in humans. A needle is inserted into the jugular vein, guiding a catheter through the right atrium and right ventricle of the heart to gain access to pulmonary artery. The catheter is connected to a pressure transducer, which measures the pressure within the pulmonary artery. The PAP score is determined by taking the mean of the systolic and diastolic pressure. Sanitation is obviously of upmost importance during the test.

In spite of the delicate nature of the procedure, a qualified veterinarian working on properly restrained, cooperative cattle can perform the test within minutes, as demonstrated during the workshop. “PAP scoring has a 75 percent to 95 percent reliability of predicting problems when performed at the proper elevation,” Dr. Abbey told his audience.

The release of the first research EPDs for PAP is intended to promote interest and feedback, with hopes of gaining more needed data from Angus breeders. Kelli Retallick, AGI director of genetic service still recommends PAP testing for animals in high elevations and encourages producers to report the scores to the American Angus Assoc. “We cannot find SNP genetic markers without physical data,” Retallick says.

Angus breeders who are not located in the states associated with High Altitude Disease may question the importance of this new set of EPDs, but the market for Angus genetics is national in scale, with animals traveling coast-to-coast both as seedstock and as feeders destined for beef. Understanding the genetic connections of pulmonary hypertension thus has potential relevance for the entire Angus industry.