PAP Testing

As a veterinarian I am often asked about PAP (Pulmonary Arterial Pressure) tests on cattle and how to interpret the results. Unfortunately, as in much medicine there seems to be much confusion and misunderstanding surrounding pulmonary arterial pressures. PAP measurements are taken to identify which animals are more likely to be able to handle high altitude without undue high pulmonary arterial pressure elevations associated with the decrease in oxygen concentration at altitude. High pulmonary arterial pressures and the cardiovascular changes that go with it are a leading cause of brisket disease in cattle. It is normal physiologic response for PAP to increase at altitude to accommodate the decreased oxygen availability, however it is the exaggerated response that some animals have that lead to high PAP and secondary heart failure.

Normally, pulmonary arterial pressures increase with higher elevations. A 1 to 2 mm pressure change is expected for each 1000 ft. Increase in elevation. Therefore, a bull that tests well with a pressure of 38 at 5000 feet in elevation could easily have a test in the upper 40’s at 8,500 feet and still be considered good. Cattle that have been at altitude and tested have a much greater likely hood of an accurate test than those tested at much lower altitude. It is important to interpret the score considering the altitude that the cattle were at and the test was performed. It is impossible to interpret PAP scores without taking into consideration the altitude that generated those scores. The higher the altitude the higher a normal pap score is and accuracy increases.

I have been asked recently with the difficulty in interpreting PAP score should we just use the PAP EPD to guide in high altitude selection. PAP EPD is and will continue to be a great tool to genetic selection. However, as with most tools it has limitations. The EPD is generated with the aid of physical PAP pressures taken as yearlings and the addition of genetic tests used to indicate the presence of genes associated with excessively high pulmonary arterial pressures. This presents some issues. It is heavily dependent on cohort data. It is not improbable that EPDs will change substantially and become more accurate as more data becomes available. Calves that may have been culled or have died from high pulmonary arterial pressures may not show in the data as PAP scores are generally done on yearlings. Subsequently, this lack of data may skew the EPD until more data from more years is available. Because of this the EPD may have a latency that over time should correct itself, however, may currently misrepresent a new bull to the genetic pool. We have all seen bulls that the EPDs change substantially from the