A new study shows the connection between cattle with high mountain disease and decreased feedlot performance and carcass quality, even when finished at low elevations.
This research, conducted at Colorado State University, examined the performance and carcass traits from high-elevation regions in relation to pulmonary arterial pressure (PAP) measurements.
High mountain disease (HMD), also known as brisket disease or high altitude disease, can occur in cattle raised at high altitudes — about 5,000 feet above sea level and higher.
“In geographical regions above 5,000 feet, high altitude disease is an epidemic which causes about five per cent of cattle residing in these areas to die annually from pulmonary hypertension,” said Emma Briggs, graduate student in bovine breeding and genetics at Colorado State University, during the Beef Improvement Federation’s 2020 symposium.
HMD is caused by hypoxia-induced pulmonary hypertension, leading to the failure of the heart’s right ventricle. With lower oxygen content in the air at high elevations, less oxygen may reach the lungs and pulmonary artery. As a result, the pulmonary artery constricts, which makes it more difficult for the heart to pump blood through the lungs.
A major symptom of pulmonary hypertension is large brisket edema, a result of the hydrostatic pressure that comes with right ventricle failure, Briggs explained. Other symptoms may include decreased appetites, lethargy and large jugular distension.
While this used to be considered more of a regional concern, HMD is receiving more attention beyond the Rocky Mountains and other high-elevation areas as cattle from these regions are sold to feedlots at lower altitudes.
“We see that high elevation cattle with high pulmonary arterial pressure, when we bring them down into lower elevation feedlots, they suffer from poor cardiopulmonary health, poor feed efficiency as well as poor carcass quality,” said Briggs.
Pulmonary arterial pressure can be used to identify animals at risk for developing pulmonary hypertension and to select for cattle better adapted to high elevations. This is measured by inserting a bore needle into the animal’s jugular, then threading a catheter down the jugular and into the heart, moving to the right ventricle to measure the blood pressure of the pulmonary artery. It’s preferred to test animals older than 10 to 12 months of age.
When tested at an elevation of 5,500 to 7,000 feet above sea level, a PAP score of 39 millimetres of mercury (mmHg) or lower suggests the animal is at low risk for developing pulmonary hypertension at any elevation. A score of 40-45 mmHg means low risk at low elevation (below 4,000 feet) and moderate elevation (4,000-5,000 feet), with a low to moderate risk at high elevation (5,500-7,500 feet) and extreme elevation (above 7,500 feet). A score of 46-49 mmHg poses a moderate risk below 7,500 feet and a high risk above that elevation, while a score of 50 mmHg or more is at moderate risk at low and moderate elevations and at high risk above 5,500 feet.
“Currently, very little research has been conducted to evaluate the genetic relationship between pulmonary arterial pressure with feedlot and carcass performance. Because of this, little is known of the potential genetic relationship that could exist between these traits,” said Briggs.
In the span of a five-year study period, steers raised at CSU’s Beef Improvement Center at Saratoga, Wyoming (elevation approximately 6,940 feet) were evaluated post-weaning at CSU’s feed intake unit at Fort Collins, then finished at the Eastern Colorado Research Center at Akron (elevation approximately 4,660 feet).
In order to study the genetic correlation of PAP scores to performance and carcass traits, researchers ran a series of five-trait models. Each model included PAP, average daily gain, average dry matter intake and weaning weight, and in each model a single carcass quality trait was included as the fifth trait. The carcass traits studied were marbling score, ribeye area, hot carcass weight, back fat and calculated yield grade.
In analyzing performance traits, researchers found a low genetic correlation between average daily gain and PAP. However, average dry matter intake had a more substantial correlation.
“These results will suggest that cattle with higher PAP scores would be the traditionally less efficient animals at converting feed when compared to lower PAP contemporaries,” said Briggs.
The genetic correlation between PAP and the carcass traits measured had a wider range. While marbling had a lower correlation, there was greater correlation to hot carcass weight and calculated yield grade, and ribeye area and back fat were negatively correlated. This relationship, she said, suggests that cattle with lower PAP scores are more likely to finish with heavier muscled, leaner carcasses than animals with high PAP scores.
“These results could suggest that high PAP cattle could be potentially using excess energy towards their cardiopulmonary vasculature system, resulting in these animals which are less feed efficient when you put them in moderate elevation feedlot settings that finish out with marginal carcass quality.”
Briggs said there’s both good and bad news in these findings. “Feedlots can purchase cattle from high elevation producers with selection pressure for pulmonary arterial pressure in their herd and in their individual breeding objectives without subsequently having undesirable feedlot and post-harvest trait performance,” she said.
“Unfortunately, looking at these results as well, we could suggest that cattle who are culled from these operations because of high PAP scores and are then sold or moved to a more moderate elevation operation could have the potential for a decrease in feedlot performance as a lighter- muscled carcass.”