High altitude disease, also known as brisket disease, is a condition predominantly in cattle that occurs in a percentage of cattle maintained and managed above 6,000 feet. Cattle seem to be the species that is most susceptible to high altitude disease, and the condition exists mostly in the Rocky Mountain region of Wyoming and Colorado, with smaller areas in New Mexico as well as Montana. Estimated death loss in high altitude herds (born, raised and managed at higher altitudes) range from .5 to 5%. However, the death loss and impact of high elevation can be much greater when cattle raised and selected in lower elevations are moved above 6,000 feet.
Certain aspects of high altitude disease are still not completely understood, but the basic model is this: Cattle raised in high elevations are exposed to a low oxygen (hypoxic) environment. This lower concentration of oxygen can trigger a response in lung tissue that narrows the small blood vessels of the lungs, making pumping blood through the lungs more difficult. The increased blood pressure required to pump blood through the lungs results in a condition referred to as pulmonary (lung) hypertension, or markedly increased blood pressure in the arteries feeding the lungs, known as pulmonary arterial hypertension, or high Pulmonary Arterial Pressure (PAP).
Incidentally, calves and young animals that were treated for respiratory disease or pneumonia earlier in life may also be at higher risk for high PAP scores, as lung damage associated with pneumonia can also lead to higher pulmonary blood pressures. As high PAP conditions continue, the animal tries to adapt. The right ventricle of the heart, responsible for pumping blood into the lungs, becomes enlarged. Continued high PAP conditions lead to enlarged lungs, diarrhea, and the characteristic fluid build-up in the brisket region, as the heart struggles to provide adequate circulation.
PAP testing has become a common selection practice for seedstock herds that are managed at high elevations, but Pulmonary Arterial Pressure (PAP) testing has it's specific challenges.
First, the testing procedure is invasive, and requires using a large gauge needle to penetrate the jugular vein, and passing a catheter line through the needle into the jugular, the vena cava, right atrium of the heart, right ventricle, and finally into the pulmonary artery. At that point, an oscilloscope measures a high, low, and average blood pressure. Proper placement of the catheter is critical, because poor placement of the catheter can lead to inaccurate readings. In addition to the procedure, cattle must be maintained at a high elevation for a period of time prior to testing to allow the animal to react to the hypoxic environment before measuring PAP. This eliminates ability to test nearly all of the popular sires and sire lines. High elevation seedstock producers are forced to take risks when sampling new A.I. sires or bloodlines, unsure of whether or not untested sires are susceptible to high PAP scores.
Although high altitude disease can have a major impact on ranches in Wyoming and Colorado, the problem is somewhat localized, unique to those high elevation areas. Federal research funding to study PAP testing has been limited at best. Federal grant coordinators look at the relatively small affected area, the impact predominantly on beef producers, and they tend to select grants with more national impacts.
Recent studies at the University of Wyoming (UW) have tried a newer approach at receiving funding. Drs. Mark Stayton and Richard McCormick have studied cardiac muscle stress, injury and repair processes for many years. Their collaborative research has focused on factors causing cardiac damage, and how cardiac muscles respond and repair. An area of human health related to their research focus has been a human illness known as pulmonary arterial hypertension (PAH) which very closely resembles brisket disease in cattle. Dr. Stayton and his research team have taken the information known about the human condition PAH, and applied the same molecular techniques to blood and tissue samples from cattle.
Their preliminary research findings have found similarities between the molecular alterations known to contribute to PAH, and the same decreased expression of receptors and increases in specific cellular proteins of cattle susceptible to high PAP. These preliminary findings are an initial positive step into better understanding susceptibility to high PAP, and selecting and managing for PAP in high altitude herds. Perhaps the next step is to build on this link between the human disease PAH, and the similar findings in high PAP cattle, and approach funding from a newer human health perspective. We are still a long way from understanding the cellular changes and even farther from developing diagnostic tests, but at least the initial research seems positive.
This preliminary PAP progress report was published in the UW Animal Science Annual Department Report 2010, available through the department, and soon to be available on the UW Animal Science Web site.