Elevation effects: Holt educates producers on HMD

With Wyoming’s lowest elevation sitting at 3,099 feet above sea level and the average elevation at 6,700 feet, according to the U.S. Geological Survey, cattle producers must pay particular attention to their cattle to protect against High Mountain Disease (HMD).
    HMD, also referred to as brisket disease, dropsy, high altitude sickness or big brisket, is a common condition that affects cattle at high elevations.
    “High elevation is described as 5,500 to 6,000 feet,” says Colorado State University College of Veterinary Medicine and Biomedical Sciences Assistant Professor Tim Holt, “but I’ve seen high altitude sickness as low as 3,500 feet.”
    Holt has dedicated part of his career to researching HMD and educating producers in high-elevation regions about the disease and its potential impacts.
Living to 5,500 feet
    When cattle, or any other mammal, are moved to high elevation, they have the potential to become hypoxic, explains Holt. “Cattle seem to be prone to hypoxia, which is the lack of availability of oxygen to the body.”
    “Every mammal ex-posed to hypoxia reacts in the same way, and that is by looking for a way to become more oxygenated,” he continues. “They pick up the fact that they have low oxygen levels in their system, so their heart rates might increase, their respiratory rates might increase, and there is constriction in the lung.”
    By constricting, the lung forces blood to the top of the organ, which is more oxygen-rich. This response is called pulmonary vascular shunting.
    “Every animal does it, but cattle do it at an astronomically rapid rate – they hyper react,” Holt says. “These hyper-reactors respond to such a degree that they develop pulmonary hypertension. If an animal is hypertensive, they can go into secondary congestive heart failure and die.”
PAP tests
    The pressure in the pulmonary artery can predict whether an animal is hypertensive, and using pulmonary arterial pressure (PAP) testing, Holt looks for animals that shouldn’t be used in high-altitude operations.
    “I put a needle into their jugular vein, and I put a cardiac catheter through the needle,” says Holt, explaining the testing process. “The catheter is fed through the right ventricle of the heart and into the main pulmonary artery.”
    At the main pulmonary artery, Holt measures blood pressure to determine if an animal is normal or hypertensive.
    “In other words, I am looking for if the animal has a lot of constriction and if it has lost lung space,” he adds. “Those animals that have pulmonary hypertension have a score of 50 millimeters and above.”
    Holt mentions that the age of the animal at the time of testing is an important consideration, and animals tested at 12 months of age or younger are less predicable and show greater variation.
    While there is some breed variation to susceptibility for HMD, Holt notes that all cattle breeds and classes are prone to the disease, and it has some expensive ramifications for high altitude herds.
    “Cattle losses from this disease alone can result in three to five percent of a calf crop,” wrote Holt in a 2007 paper, also mentioning that in one instance, losses were seen at as high as 25 percent of the calf crop.
    For cattle in pastures, he notes that there are several signs that producers can look for that may indicate HMD.
    “Some of the classic symptoms are a pulsating jugular vein or jugular vein enlargement. They can also get edema, or fluid in their chest – that is where the term brisket disease comes from,” explains Holt. “Other symptoms include diarrhea, abdominal swelling, bulging eyes, extreme weakness, lethargy and acute death.”
Research efforts
    “We have a lot of research going on right now,” comments Holt, noting that genetics and confounding factors are among the primary research targets currently.
    “We are going to continue to chase and better understand the genetics of this disease,” Holt says. “We are chasing down sire information and female information so we can track down the genetics.”
    Looking at confounding factors also plays a major role in research, as scientists are seeking information about what other qualities or traits, aside from genetics, impact the disease.
    Research is being conducted related to the effects that concurrent illness and characteristics of cattle have on HMD.
    “We are looking into this disease more than just PAP testing at high altitudes. We are looking at what contributes to it or what might make an animal more prone to it,” he notes.
    Human cardiologists have also joined the efforts in HMD research in cattle.
    “The disease is quite common in humans as well, and researchers are looking to see if cattle could be a model for the human process of the disease,” explains Holt. “They are going with us for testing and collecting data. They are extremely interested in trying to find out all the intricacies of the disease that we don’t know. It is very exciting.”
    Saige Albert is managing editor of the Wyoming Livestock Roundup. Send comments on this article to saige@wylr.net.