by Cheryl Kepes
photos courtesy Michael and Vikki Ripp and Dr. Tim Holt
The heart of the matter about high altitude disease.
There is majesty and beauty embodied in the mountains nestled in the Western U.S; so much awe and wonder wrapped up in their soaring peaks. However, amidst the splendor of the upper elevations, a silent killer lurks in cattle herds. The threat to cattle grazing on the mountainsides comes in the form of high altitude disease, more commonly known as brisket disease or mountain sickness.
In recent years, due largely to the efforts of veterinarian Dr. Tim Holt, and ranchers in mountainous regions, a test for an animal’s susceptibility to high altitude disease has caught the attention of producers worldwide. The American Angus Association added an EPD indicating an animal’s genetic predisposition to high altitude disease and ongoing research suggests that same group of genes may cause feedlot animals to be more susceptible to congestive heart failure.
Impacts of the Disease
Michael Ripp knows all too well the devastating impact high altitude disease can have on a herd. Michael and his wife, Vicki, operate MVR Ranch in Delta, Colo., where in the summer months they graze their cattle up to 10,000 feet in the mountains. “It is common to find calves up on the mountain that are suffering from brisket disease,” Michael Ripp said. “If they are too far gone, then they won’t even move; and they are going to die right there.”
Twenty-six years ago, the Ripps bought their first registered Angus and joined the Western Colorado Angus Association. The couple has been working to educate other ranchers about high altitude disease ever since. “It is important to a lot of cattlemen in the high altitude areas and I believe it is becoming significant even for cattle in lower altitudes,” Ripp shared.
When the Ripps started managing their herd at high elevations, they turned for help to the person who knows more about it than anyone in the world.
Dr. Tim Holt, veterinarian and professor of livestock medicine and surgery at Colorado State University, is the leading expert on high altitude disease. He started researching high altitude disease 42 years ago. Each year, Dr. Holt travels through Colorado, Wyoming, Idaho, Montana, Utah, Nevada, New Mexico, and to other countries testing cattle for genetic susceptibility to brisket disease.
In his decades of work, he’s tested more than 488,000 head. “I think the intriguing thing about it is, one, I love the physiology of the heart and lungs, that is my passion,” Dr. Tim Holt said. “And two, it gives me a step to possibly help the people that I love hanging out with and that is the rancher.”
One way to think about high altitude disease is to compare it to pulmonary hypertension seen in humans. “Pulmonary hypertension is one of the number one killers of humans. We don’t even know we have it and we soon fall over with congestive heart failure,” Dr. Holt said.
In cattle, the deadly disease strikes in a silent and similar way. When cattle are in high elevations their oxygen availability drops, just like in people when they travel thousands of feet above sea level. The technical term is hypoxia, meaning the body is oxygen starved.
When this occurs, the vessels in the lungs take over trying to push blood to the more oxygenated parts of the lungs. Humans, for the most part, can efficiently do this; however, cattle cannot. The problem is exacerbated in cattle due to their small lung size compared to their body weight.
As cattle work to relocate oxygen in their lungs, they do so at an exaggerated rate causing their vessels to constrict and thicken, further limiting blood flow to the lungs. This triggers the right side of the heart to beat overtime in order to compensate. “The heart is under a lot of pressure to try to continue to push blood up into the lungs and that’s where the term pulmonary hypertension comes from,” Dr. Holt explained.
Eventually, too much pressure builds up and the heart gives out. Some of the physical signs of high altitude disease can include fatigue, bulging eyes, diarrhea, difficulty breathing, and swelling in the neck and chest area. The collection of fluid in the brisket gives the disease its common name.
If caught early enough, animals can be treated. The treatment includes moving the animal to a lower elevation, giving it antibiotics, diuretics, and/or oxygen therapy. Typically, ranchers don’t discover their animal is sick, until it is too late.
Identifying High Risk Animals
MVR Ranch is just one of hundreds of stops Dr. Holt makes each year to perform the pulmonary arterial pressure (PAP) test on bulls and females managed in high altitudes. The PAP test measures the pressure on the pulmonary artery and indicates if the animal has pulmonary hypertension. A reliable PAP score can also assist a producer in determining if the animal is more genetically resistant or susceptible to pulmonary hypertension.
The protocol and equipment utilized for the PAP test is similar to the medical procedure used to test humans for pulmonary hypertension. During a PAP test, a catheter is threaded through the animal’s jugular vein and down to the right ventricle, through the ventricle and into the pulmonary artery where the pressure between the heart and lungs is measured.
For the PAP test to be the most accurate, it must be conducted at a high elevation. Most PAP tests are conducted at 5,000 feet or higher. The Ripps PAP test their herd at 9,400 feet after the animals have been there all summer. Like other ranchers, they use the PAP scores to guide culling and breeding decisions.
According to Dr. Holt, no one breed is resistant to the effects of high altitude disease. However, some animals seem to be more naturally resistant to the effects of high altitude.
PAP Scores Influence Management
The Ripps’ keep females with low PAP scores for replacements. “I test everything because I am trying to breed cattle that are good at high altitude. So, the female is half of the equation, she contributes half of the genetics, and there is a genetic correlation to PAP scores,” Michael stated.
MVR Ranch’s bull customers want bulls with low PAP scores and will pay more for them. “People who are aware of this situation and all the things that are involved with it, will look for cattle that have low PAP scores and are tested at the highest altitudes that they can find,” Michael said. Animals on the Ripps’ ranch with high PAP scores are sold for slaughter.
Dr. Holt says the PAP test serves as a guide for ranchers wanting to produce cattle that will thrive at high altitude. “We are genetically selecting and genetically building a bovine herd that is resistant to the effects of altitude by doing the PAP test,” Dr. Holt said.
The development of a herd that is naturally resistant to high altitude disease can be economically beneficial to producers. “I have seen death losses from brisket disease as high as 23 to 26 percent of their calf crop. If I can get that down to 1 to 3 percent, then we make them more of a profit,” Dr. Holt added. “And it makes me feel good that I can actually help them build this in the altitude.”
Future Applications of PAP Testing
Currently, ongoing research is looking at PAP scores relative to feedlot deaths at lower elevations. In addition, researchers are analyzing the impact high PAP scores have on growth rate, marbling, grading, and other traits.
Veterinary students at Colorado State University travel with Dr. Holt to learn how to conduct PAP testing. The more veterinarians skilled in the procedure, the more ranchers who can benefit from the information the test reveals about their cattle.
Dr. Holt plans to travel to Peru and South Africa to teach veterinarians in those countries about PAP testing and to help them learn how to select animals that are more genetically resistant to high altitude disease.
Though Dr. Holt, the Ripps, and other ranchers are dedicated to spreading the word about PAP testing and have made big strides in the last few decades, they hope their message reaches even more people in the cattle industry in the years to come.