The American Angus Association has released EPDs (expected progeny differences) from their research analysis on pulmonary arterial pressure (PAP), which is used as an indicator trait for pulmonary hypertension in cattle managed at high altitude. The Angus Association’s release of the new EPD is in response to members’ needs who manage cattle at elevation.
Pulmonary hypertension has been associated with decreased performance and death loss on high altitude cattle for 100 years. It is often referred to as “brisket disease” because of the associated edema in the brisket and chest cavity that results from high PAP. This compounds the already existing problem of high PAP cattle’s excessive heart contractions and stretching of the heart muscle in an effort to keep the body oxygenated. When the heart chambers exceed capacity, the heart wall thickens, which can result in heart failure and death.
Pulmonary hypertension has become a major concern to all of the cattle industry due to the unacceptably high levels of cardiac-related death loss now occurring in feedlot cattle at lower elevation.
This is a more recent phenomenon that has coincided with cattle being fed to heavier weights with a fatter end point as well as the dominance of Angus influence in the country’s commercial cow herd. However, the American Angus Association is quick to point out the relationship between high altitude pulmonary hypertension and feedlot pulmonary hypertension is not fully understood and needs further research to determine if and how the two diseases are related.
Angus’ PAP EPD is based on the records of 4,700 animals that have had yearling PAP scores taken at altitudes of 5,500 feet or higher. The heritability of the trait is 0.36, which is slightly higher than most growth traits. Therefore, progress can be made through objective selection.
In addition to the high-altitude data, another 3,000 records on cattle managed at moderate altitudes of 4,000-5,499 feet were used in the calculations as a correlated trait. The correlation between these lower elevation cattle with the high-altitude cattle is high, being over 0.80, although the heritability drops considerably to 0.16 at lower elevation.
The calculations producing the EPDs is a single-step, genomically-enhanced model, which provides enhanced relationship information between animals and increased accuracy.
Because this initial PAP EPD release is a prototype, only certain producers will be receiving the EPDs. The EPDs released will be to producers for their animals, upon which they have submitted a PAP score along with the progeny’s sires. In addition, EPDs will be released to owners of AI sires that have an accuracy for the trait of 0.40 or higher.
The association’s goal is to get feedback on the predictions as to whether they are lining up with what is being seen in the field. Based on producer feedback, the predictions will be enhanced over time.
With the release of the PAP EPD, the association also hopes to spur submission of needed data. It will be accepting historic data through July 2019. It is also looking forward to an influx of data from Colorado State University’s research herd and programs, which will significantly increase the number of records the genetic predictions are based on.
After this grace period where producers can send in historic data, the association will only be accepting newly-collected data from trained veterinarians. Although the association’s genetic prediction is currently based only on yearling data (320 to 720 days), producers with weaning PAP scores are encouraged to submit them so their usefulness can be researched.
Kelli Retallick has been the point person at the American Angus Association on the project, and the research conducted in association with Colorado State University. She is quick to point out the necessity of collecting phenotypic PAP scores when making selection decisions. This is because, in addition to the genetic component of PAP, any environmental influence such as respiratory disease, parasites, or dust that inhibits lung function will also significantly increase PAP scores. This can result in an animal that is not suitable to be run at elevation despite having acceptable genetics for the trait.
Retallick likens it to scrotal circumference and breeding soundness exams. Although a bull may have a desirable scrotal circumference EPD, it still should have a breeding soundness exam done. The goal is to get cattle bred, which a current breeding soundness exam will help confirm, while the scrotal EPD will help determine the progeny’s reproductive soundness.
The same dynamic exists for the PAP EPD. A desirable PAP EPD will help determine progeny’s desirability for the trait, but if an individual animal has been compromised with bovine respiratory disease or some other potentially lung-damaging condition, it will not be suited to be managed at high elevation regardless of its EPD.
With the American Angus Association’s release of its research PAP EPD, the association continues to lead the industry in the objective genetic description of novel traits. Another example is their earlier release of foot score EPDs. Their overall goal is to enhance the profitability of producers utilizing Angus genetics.
In addition, when the relationship between high altitude disease and feedlot pulmonary hypertension is fully understood, PAP EPDs may become even more critical to the future of a profitable beef industry. — Dr. Bob Hough, WLJ correspondent
