The value of PAP testing cattle in Wyoming

By Chance Marshall 

It’s common for cattle producers in many parts of the state to run cattle on a high-elevation grazing allotment during the summer months. The feed quality on these allotments can be fantastic, but there are definitely some challenges to come along with it.  

When determining what types of cattle are best suited for the environment in Wyoming, beef producers like to discuss breeds, cow size, fertility, efficiency and hardiness. However, another characteristic is a significant part of discussion in many parts of Wyoming – pulmonary arterial pressure (PAP) scores. PAP testing gives high-altitude beef producers a prediction of how well suited their cattle’s heart and respiratory systems are for Wyoming’s high places.  

High-elevation disease 

A PAP test measures the blood pressure in the pulmonary artery and estimates the force required to push blood into the lungs at high altitude. In Wyoming, it’s not uncommon for cattle to graze summer pastures up to 9,000 feet or more, where there is less oxygen in the air.  

Cattle grazing at increased elevations – above 6,000 feet – whom are not equipped to deal with lower oxygen levels, are at risk of brisket disease, increased morbidity and decreased overall performance. 

When oxygen is too low for certain cattle, it causes arterial walls to thicken and decrease in diameter, making it difficult for the heart to pump blood into the lungs. This extra effort eventually causes the right ventricle of the heart to enlarge and lose its ability to contract.  

As blood pressure builds, the valves in the heart begin to fail and leak. Fluid then congregates in the lower portions of the animal, which are most commonly the neck and brisket area – hence the name brisket disease. Fluid will likely continue to build and eventually spread to their jaws and belly. 

The most effective treatment for cattle exhibiting symptoms of brisket disease is to immediately move affected cattle to lower elevations, treat them in a hyperbolic chamber to increase oxygen levels and administer diuretics and antibiotics. However, once visual signs are noticed, it’s often too late.  

Cattle are commonly found dead with no visual symptoms. Even if cattle survive or are only moderately affected, economic losses can be expected due to poor performance. 

Reproductive considerations 

Using sires with desirable PAP test results can be helpful in decreasing losses to brisket disease, as these traits have been determined moderate to highly heritable, with heritability at 40 percent or greater.  

The measurement is taken by inserting a large needle with a catheter into the jugular vein. The catheter is then fed into the right ventricle of the heart, through a valve and into the pulmonary artery. A pressure transducer then measures the systolic and diastolic pressure in millimeters of Mercury (mmHg).  

The mean of the two measurements is the PAP score. PAP scores generally range between 30 and 80 mmHg. The lower the score, the lower the risk for complications due to high elevation.  

A score below 41 mmHg is generally considered acceptable, whereas, scores ranging from 41 to 49 mmHg are considered a moderate risk, especially if younger than 16 months of age. Any animal, including their offspring, with scores greater than 49 mmHg must always be considered as high-risk for brisket disease. 

PAP testing 

Researchers at the University of Wyoming have worked on developing tools to locate a “brisket disease gene.” However, a PAP test is still the best tool available to cattle producers to help predict high-altitude performance.  

A reliable PAP test result is dependent on various factors. These factors include a three-to-six week acclimation period to the elevation at which cattle are tested, the age at which cattle should be tested – it is recommended cattle be mature when tested and at least one year of age and preferably at 16 months – and tests should be done in temperatures above freezing, as extreme cold temperatures have been shown to increase PAP scores by 25 to 55 percent.  

Additionally, cattle with concurrent illnesses or with excessive body condition scores may result in elevated PAP scores. Lastly, access to experienced technicians is critical in obtaining dependable results. 

Utilizing research 

Even with a reliable test, it is important for cattle breeders to consider the circumstances of where the PAP test took place. Often, guidelines for results are available and should be taken into account and compared to the environment in which the cattle will actually live in.  

PAP scores only predict survivability at the tested elevation. For example, a PAP test done in Colorado at 5,600 feet will not necessarily predict how an animal will perform on a summer forest allotment at 8,000 feet in Wyoming.  

However, some research has suggested that for every 1,000 feet increase in elevation, a one to 1.5 mmHg increase in PAP score can be expected. More research is needed to truly understand how elevation changes impact PAP scores. 

Using sires with low PAP scores is currently still the best tool available to improve success for cattle grazing high-altitude areas in Wyoming. However, it is critical for beef producers to understand where and when those test results were obtained in order to avoid losses. 

Chance Marshall is a University of Wyoming Extension Agriculture, Horticulture and Livestock Systems Educator based in Fremont County. He can be reached at cmarsha1@uwyo.edu or 307-332-1018.