New research shows faster growing cattle at higher risk for brisket diseaseWritten by Gayle Smith
When cattle producers started PAP testing bulls for high altitude disease, they thought the disease would eventually disappear. However, as researchers dive more into this disease, they are finding it is more complicated that they first thought.
Brisket, or high altitude disease, is pulmonary hypertension that occurs when there is increased pressure in the pulmonary artery. The pulmonary artery takes blood into the lungs to get oxygenated. When cattle have high altitude disease, blood backs up in the venous system causing fluid to build up. This causes brisket edema, mandibular edema or belly draggers in cattle.
When cattle experience pulmonary hypertension, the right side of the heart vessels narrow or constrict causing congestive heart failure, if it gets bad enough.
According to Colorado State University (CSU) veterinarian Frank Garry, brisket disease is not unique to high altitude.
“When it occurs at high altitude, it is because high altitude creates the problem,” he said. “That’s when it's called brisket disease at high altitude.”
Discovering brisket disease
This condition was first discovered in Colorado over 100 years ago when some South Park ranchers asked CSU researchers to determine why their cattle were dying.
“Over the next 30 to 40 years, we determined why it was occurring and developed the Pulmonary Arterial Pressure (PAP) test, which allows us to detect the problem. By 1960, we had determined the pathological pathway,” he explained.
Low oxygen in the environment at high altitude causes the bovine lung to respond to the high altitude by constricting the arteries.
When the arteries are constricted, it puts pressure on the heart, Garry said. Changes in the arteries lead to narrowing of the blood vessels, putting increased pressure on the right side of the heart.
“Some animals do okay with pulmonary hypertension over long periods of time,” he said. “Others will succumb to right side heart failure and brisket disease.”
At one point, scientists told producers to select bulls that, at a high altitude, have low pulmonary pressure for this moderately heritable trait. But it wasn’t enough.
“We don’t dig ourselves out of a reproductive problem by just breeding,” Garry said. “It takes generations of time. We thought that if producers bred their cows to low PAP bulls over time, this problem would just go away.”
What they have found is brisket disease is a progressive condition.
“We have producers who have been testing bulls for 30 years and still have problems with this disease,” Garry explained.
When one of these producers started reporting problems with what he called “summer pneumonia,” Garry sent one of his graduate assistants to investigate. Utilizing producer surveys, pathology and physiology, Garry said his graduate assistant was tasked with finding out if these calves were actually succumbing to summer pneumonia.
“At first, producers thought they just had a toxic plant problem, which they quickly found was not the problem,” he said.
The cattle had more problems with pneumonia and pulmonary hypertension.
Ranching at altitude
“High altitude ranchers face more liability,” Garry said. “It is a tough environment for the cattle to grow up in.”
After performing necropsies on as many calves as possible that summer, it was determined that half had died from bovine respiratory disease (BRD) and the other half from pulmonary hypertension.
“These calves didn’t look like belly dragger calves or calves with classic brisket disease,” Garry said.
Identifying brisket disease
The calves did show higher levels of oxygen stress than researchers had anticipated, which showed that brisket disease is not just a high altitude problem.
“The clinical signs are so similar to pneumonia that it is hard to distinguish between the two, particularly in the early clinical stages,” Garry said. “However, the diseases look different histologically.”
“We have initial evidence that the cardiopulmonary system is undersized for the oxygen requirement,” he continued. “Cattle get different pulse pressure. Blood doesn’t circulate as well at high altitude.”
At this point, PAP testing bulls is still the best tool available to address the disease.
“Brisket disease is increasing in the cattle population, regardless of altitude,” Garry said. “If a producer suspects summer pneumonia, it is really important to get a veterinarian to do a necropsy.”
“It is important to know if we’re are dealing with infectious pneumonia or pulmonary hypertension,” he said.
Garry fears cattle producers are dealing with a similar problem that affected the broiler industry years ago. Broilers were dying because they had been bred for too fast of a growth rate. It makes a difference how cattle are bred, where they are raised and where they go to the feedlot.
Garry said in Nebraska feedlots at 3,500 feet, nearly-finished cattle were dying from high altitude disease that had never been above 4,000 feet.
“Death loss attributed to heart failure in three northern Colorado feedyards in 2014 accounted for 7.1, 9.9 and 6.5 percent of the moralities,” Garry shared. “Management and breeding both figure in to this problem. It is not caused by a single trait.”
The problem may be with the cattle growing really big, really fast. The average live market weight has increased 48 percent since 1944.
“The risk of dying from heart failure has doubled in the U.S. and Canadian feedlots since 2000,” Garry said. “There is a tendency for feedlot cattle to die from heart failure later in the feeding period.”
Cattle pulled and treated for bovine respiratory disease were also found to be more likely to die from heart failure.
Garry said the bovine lung has a decreased alveolar surface area in proportion to body weight, and the cardiac mass, as a proportion of hot carcass weight, is smaller than almost a century ago.
“If we breed fast-growing cattle, we should expect this to continue to be a problem in the feedlots,” Garry summarized. “My recommendations are to PAP test cattle and be aware that if we’re at high altitude and breeding for excessive growth, we are putting cattle at increased risk for physiologic stress. Do things to prevent infectious disease because those diseases cause inflammation, and the combination of these things causes this problem.”
It is important to test yearling bulls before purchasing them for high altitude cattle operations. If the bull tests high at a low altitude, don’t purchase it, Garry said. If the bull tests reasonable at a low altitude, retest it at a high altitude before purchasing it.