At Gittleson Angus we have been PAP testing our cattle for over twenty years. We PAP test all of our females as well as our bulls. Our calves are all tested at weaning and then again at 12 months or older. Below is an explanation of PAP and Bovine High Mountain Disease provided by Dr. Tim Holt, DVM and Colorado State University.
Pulmonary Arterial Hypertension resulting in congestive Right Heart Failure (RHF) in cattle is a very common condition seen in the high altitude regions (>5000 feet) of Colorado, Wyoming, New Mexico, and Utah, with Colorado being the main area of focus with this disease. Pulmonary arterial hypertension is also known as Dropsy, Bovine High Mountain Disease (BHMD), Big Brisket or Brisket Disease. Brisket disease or High mountain disease is due to a hypoxic-induced pulmonary hypertension with subsequent right ventricular failure. Brisket disease is the common terminology used and is derived from the presence of ventral edema in the brisket region secondary to the severe intravascular hypertension and the loss of fluid into the extravascular spaces. The signs and symptoms seen may be lethargy, weakness, collapse, diarrhea, bulging eyes, death, and peripheral pitting edema in all ventral aspects of the animal with the brisket region being most pronounced.
Brisket disease has multiple factor causes including environmental conditions as well as overall health of the animal. Susceptible animals have increased pulmonary artery pressure (PAP) readings that worsen in response to an acute or chronic hypoxemic exposure. Furthermore, in cattle, it has been found that PAP increases with age, but the increment is less in high altitude adapt animals than in animals brought to high altitude acutely. In genetically susceptible herds the losses can easily exceed 5%. Given the size of the cattle industry in high altitude regions in Colorado and other mountainous states, these percentages represent significant economic loss. A common denominator in the maladaptation to high altitude living in cattle will manifest itself as increase in pulmonary arterial pressure as a result of pulmonary hypertension. Therefore it is possible that genetically susceptible animals have an increased pulmonary artery pressure (PAP) measurement. Those cattle that are genetically susceptible are more prone to developing the BHMD in the presence of any other factors. Pulmonary hypertension is defined as a prolonged increase in the arterial pulmonary pressure in the main pulmonary artery at rest and exercise as measured by a pulmonary artery catheter.
The altitudes at which cattle are affected is generally 5000 feet or greater with 7500 feet and greater becoming the most critical elevations. Cattle in Colorado are commonly grazing at 9000-12,000 feet which the disease can become very dominating and costly. The development of the Pulmonary Artery Pressure (PAP) measurement has documented that the pathogenesis of this disease is heritable. By utilizing the PAP measurement it is possible to predict which animals are experiencing pulmonary arterial hypertrophy and are susceptible to developing pulmonary hypertension. By utilizing PAP testing diagnosing and predicting the presence of pulmonary artery hypertrophy and the early signs of congestive right heart failure is possible, thus minimizing severe economical loss. The PAP measurement allows the ability to genetically select more resistant pedigrees of cattle for breeding purposes for the use in high altitude.
Utilization of the PAP measurement is useful in selecting breeding stock for high altitude use often eliminating those animals prone to develop BHMD. By selecting animals with low PAP measurements a genetic selection could be done. There is no question that the adaptability to high altitude living has a genetic determination in cattle.
To accurately use and evaluate a PAP score/measurement, important factors must be considered. Buyer, Seller, and Veterinarian must be aware of these factors and understand how they play a role in correctly evaluating a PAP measurement.
1. AGE OF ANIMAL BEING TESTED
When evaluating a PAP score, the age of the animal at the time of testing should always be considered. It has been determined that the accuracy level of the Pap test is less predictable for those animals tested at or younger than 12 months of age. Variation in scores of those animals tested at younger than 12 months was much greater than those of older animals were. Animals tested at 16 months of age and older appear to be the most consistent and accurate. In those tested less than 12 months of age, predicting the PAP test score as the animal ages has been difficult and inconsistent.
Special consideration should be made for those animals tested at or less than 12 months of age. If the animal scores in the 30-35mmHg range the test appears to be approximately 80% accurate in predicting the PAP score to remain within an acceptable level for high altitude use. If the animal scores 35-40mmHg the accuracy level is approximately 82% for the PAP to remain in the acceptable range for high altitude. Any score above 41mmHg seems to be questionable to what will happen as these animals age and it is strongly recommend that these animals be retested prior to use. Animals testing over 45mmHg should always be considered a risk for high altitude use.
2. ELEVATION OF TEST
Some animals appear to be very prone to the congestive heart failure while others can live at high altitude and an elevated PAP test for years with no problems. It is for this reason the elevation of the test is important. It has been determined that the low oxygen stress (chronic hypoxia) needed to stimulate problems is not present until approximately 5000 feet elevation. This factor makes it impossible to accurately PAP measure an animal lower than 5000 feet. It is also important that this Pulmonary Artery Hypertrophy secondary to high altitude hypoxia is chronic in nature making it a necessity for the animal to be in altitudes greater than 5000 feet for a minimum period of 3-4 weeks prior to testing. The longer the animal is in high altitude prior to testing the more reliable the test is.
It has been demonstrated that a PAP score will go up as the animal is taken to a higher altitude. It is for this reason elevation of the test site must be considered. For simple guidelines, the animal should be tested at an elevation of at least 5000 feet. The higher the elevation of the PAP test the more accurate the results. Look at the PAP score and the elevation at which it was taken and consider the elevation the animal will be living.
In one study conducted in Laramie Wyoming it was shown at a statistically significant level that cattle tested at 5000 feet and moved to 6500 feet for three weeks and retested, averaged an increase in the PAP of 7.2mmHg. This variation is based on the fact that 5000 feet is the absolute minimum for testing and at this elevation the degree of inaccuracy and PAP variability is much higher. It should be recommended to all involved that cattle tested between 5000 feet and 6500 feet elevation, that the degree of variability is unpredictable and retesting is recommended. Evaluating age and elevation together is a must; if an animal less than 12 months of age is tested at elevations lower than 6500 feet the degree of inaccuracy unpredictable. It is best to think of those cattle PAP tested below 6500 feet as a screening test only and not a test validated for genetic breeding potential. A PAP test at this elevation can be accurately used to find those animals already experiencing pulmonary hypertension thus allowing management decisions at this time. The chance of getting a high false PAP reading is very rare at any elevation.
3. BREED DIFFERENCES
There does not seem to be any one breed that is resistant to the effects of high altitude. There have been high measuring animals (>50mmHg) found in all breeds tested at this time. There does, however, seem to be some breeds, and pedigrees within breeds that are more naturally resistant to the effects of high altitude. By utilizing Pulmonary Arterial Pressures, selection of more naturally resistant cattle can be done.
It is important in the evaluation of any animal originating from a low land herd (<5 000="000" feet="feet" elevation="elevation"> This innate resistance to high altitude effects is secondary to the effects of both natural selection and the culling processes by the rancher. Ridding the herd of those animals with High Mountain Disease (HMD) themselves and/or giving birth to calves that develop HMD can help to build a more naturally resistant herd in high altitude, in comparison to low land herds in which no natural selection takes places. This is an important consideration in testing and/or using animals originating from low land herds.
4. ILLNESS, VACCINATION
Since the PAP measurement is actually a measure of lung blood flow resistance, anything causing a decrease in lung space temporary or permanent can cause an increase in the PAP measurement. Any type of respiratory or pulmonary pathology can lead to an arbitrary high PAP measurement. Many of the respiratory diseases cattle experience can lead to this increase in pulmonary hypertension. If an elevated PAP measurement is thought to be secondary to a temporary pulmonary disease then retesting the animal should be done. It should be noted that PAP scores of over 50-55mmHg have never been documented as dropping to an acceptable level. It appears once the PAP measurement reaches this degree or higher that extensive pulmonary vascular damage has taken place and the animal does not return to a normal pulmonary pressure, making them a high-risk candidate for use in high elevation situations. Even though this animal may not be genetically susceptible to high altitude affects, the lung pathology has made them a risk in acquiring HMD.
PULMONARY ARTERIAL PRESSURE (PAP)
* These figures are based on cattle tested at or above 6500 feet elevation and 12 months of age or greater.
1. PAP SCORE 30-35mmHg
This is considered an excellent and highly reliable score.
2. PAP SCORE 36-39mmHg
This is considered an excellent score for any animal over the age of 12 months. If the animal is less than 12 months of age, the score is still fairly reliable but retesting prior to use is suggested.
3. PAP SCORE OF LESS THAN 41mmHg
Scores less than 41mmHg are reliable measurements in all animals greater than 12 months of age. It is recommended that yearling cattle measure less than 41mmHg (depending on altitude of the test). The variation in scores 41 and above is inconsistent and difficult to predict in some cattle as they age. Any animal measuring 41 and greater should always be retested prior to use.
4. PAP SCORE OF 41-45mmHg
This is an acceptable range for older animals i.e. greater than 16 months of age. Animals less than 16 months scoring in this range should be retested to accurately predict the future of the animal.
5. PAP SCORE OF 45-48mmHg
This is an acceptable range for only older animals that have been in high elevations for an extended period of time. Animals with this score are more susceptible to environmental stresses leading to HMD and should be considered at some risk. Elevation of test site and where the animal is located must be looked at closely for those in this PAP score range.
6. PAP SCORE OF GREATER THAN 49mmHg
Animals that score in this range must always be considered a high-risk candidate, not only for themselves but also their offspring. Many animals that have scored in this range have died of HMD.