Dr. Tim Holt received the Pioneer Award from the Beef Improvement Federation in 2018 for his pivotal role in developing and delivering a veterinary test that predicts susceptibility to pulmonary arterial hypertension (PAP). Tim conducted his first PAP test in 1980 and now has tested over 492,000 head. He and the Colorado State University (CSU) animal sciences department continue testing on sire groups and replacement heifers, tracking the heritability of the disease.
A PAP EPD was developed from the work at the university so producers could make a better genetic selection for the trait. The American Angus Association first released the EPD in 2019. Throughout 2019, a multi-breed database was established with the American Simmental Association, Red Angus Association of America and other commercial breeders, and was developed with the assistance of Tim and CSU’s work with International Genetic Solutions. Tim said the accuracy levels continue to improve with more producers volunteering their data. The more PAP data submitted to the overall database, the more accurate the PAP EPD will be.
Tim said they are currently working with the American Hereford Association, along with mixed breeds such as SimAngus and Lim-Flex, to develop a PAP EPD for their associations.
Tim said with the PAP EPD, the more positive the number, the more sensitive the animal is to altitude. For example, Tim said if the bull has a score of 9, you do not want to use that bull in your operation if you are located at a higher elevation. If a bull has a score of 1, it is still questionable whether to use that bull in a higher elevation.
“What we are looking at for a PAP EPD is a score of -1 or below; I try to push people to get -1.5, meaning that most of his offspring are passing the PAP test, and according to his pedigree, they should be somewhat resistant to the effects of altitude and hypoxia,” Tim told WLJ.
Tim encourages ranchers to use the PAP EPD when they make selections on AI bulls. He gave the example that if a bull has a PAP EPD score of 4 and they live at a higher altitude, consider not using that bull. However, if a rancher is at a bull sale and the animal has a PAP score of 41, and an EPD score of -2, Tim suggests that it may be a bull that can handle the effects of altitude. Tim said if you live at a higher altitude, it is best to utilize the actual PAP score as well as the PAP EPD, remembering that in general, the lower the PAP score and the lower the PAP EPD, the better.
Cattle with a PAP score of 34-45 are considered low to moderate risk, and those between 46-49 are considered a moderate risk when tested at an elevation of 6,000 feet or higher.
Tim said if ranchers want to develop their animals to have the potential of not dying from heart failure—he emphasized “potential,” as researchers haven’t proven it yet—then ranchers want to select bulls with a 0 or lower PAP EPD. Ranchers who plan on selling cattle in higher elevations should also do the same. If animals are going to stay at lower elevations, then Tim said the PAP EPD should not be a concern. Tim said his work with PAP and the genomic markers will be ongoing until they figure them out.
Since the development of the EPD, Tim said he started looking at feedlot deaths and developed what he called a “cardiac grading score.” Tim; the CSU animal sciences department; and Shuna Jones, USDA genetics and animal breeding veterinary medical officer, went to packing plants and examined and evaluated hearts in packing plants to see how many animals experienced cardiac change. Tim said the cardiac grading score goes from 1 to 5, with a score of 1 or 2 showing some variant form of normal and anything with a score of 3 or above showing some form of cardiac change.
Tim said he estimates losses in feedlots from cardiac failure to be $1.4 billion, which is why his team is currently conducting research in Amarillo, TX, and other feedlots across the U.S. Tim said that in addition to the cardiac grading scores, they are also looking at carcass characteristics and performing PAP scores.
“It’s costing the feedlots a tremendous amount of money and we’re trying to track the reason behind it,” Tim said. “In my humble opinion, this disease is initiated by hypoxic stress, which is the lack of available oxygen. I think we are going to find the same thing whether you are altitude hypoxic or low elevation hypoxic—it’s all resulting in the same catastrophic cardiac change.”
Tim said hypoxia could be attributable to multiple factors, including pneumonia, lung disease, fat around and within the heart muscle, altitude and obesity. Tim said their research shows that if an animal is genetically prone to the hyper response of hypoxia, then regardless of the initiating cause, the entire pulmonary and cardiac failure cascade begins.
Tim, the team at CSU and others are concentrating their research on trying to determine why some cattle on feed die late in the feeding period, and they are looking at body size relevant to pulmonary and cardiac size.
“Are the animals simply outgrowing what their heart and lungs can maintain, or are there other factors involved, such as hypoxia secondary to fat deposition in and around their hearts, as well as circulating fat causing an extreme inflammatory hypoxic effect resulting in cardiac failure?” Tim asked.
“There is still much to study, but we are certain that genetics play a significant role both in animal survival as well as cardiac failure late in the feeding period. We are certainly seeing a genetic sire correlation to both of these situations.”
Tim said they are all very excited as they look to the future and the research collaborations with CSU Animal Sciences, University of Wyoming, University of Colorado School of Medicine, U.S. Meat Animal Research Center and others.
“With everyone involved going after the same goal, we are hopeful we can put an end to late feedlot death and better understand the physiology of pulmonary and cardiac disease,” Tim said. — Charles Wallace, WLJ editor
