By Patti Wilson, Contributing Editor
A couple previous Chuteside articles have focused on maladies creeping into beef herds from dairy segments of the U.S. cattle population. There’s yet another problem finding its insidious way from the Rocky Mountain area to the Plains. This one is not contagious, nor is it related to milk cows, yet its insistent increase in feedlots reminds us that health problems tend to spread in opportunistic manners, without discrimination.
What is it?
Pulmonary hypertension (PH) has been recognized and studied for over 100 years. Until recently, it has been confined to the high mountain areas of Colorado, Wyoming, New Mexico and Utah. Elevations over 5,000 feet are considered high risk, with the incidence of PH increasing as elevations increase.
To put this as simply as possible, brisket disease is very nearly the equivalent of high blood pressure in humans. The thin air in mountainous areas contains less oxygen than lower elevations; consequently, cattle hearts must work harder to supply oxygen to organs. Over time, the heart muscle begins to hypertrophy (thicken) to the point that it becomes inelastic and can no longer adequately contract to pump blood. This is basically a form of congestive heart failure. Blood pressure builds in the now-constricted artery that carries blood from the heart to the lungs, making for a poor prognosis.
A heart that works too hard will spin off many problems. Specifically, the right side of the heart is responsible for pumping or pushing blood into the lungs. It is the most vital job within any animal’s body. With PH, a major artery carrying blood directly from the heart to lungs will respond to stress by narrowing, reducing blood flow and increasing blood pressure. The extra effort needed to pump blood through an ever-narrowing artery causes the heart wall to thicken or enlarge until it loses elasticity and effectiveness. It is a chicken-and-egg dilemma.
Eventually, blood initially pumped into the constricted artery can flow back into the heart and blow out the valve of the right ventricle. As the disease progresses into the lungs, hypertension causes fluid to leak from blood vessels into the body, causing a swollen brisket. The swelling or fluid retention can extend behind the brisket into the belly and up into the neck area. In all cases, this leads to death.
Absent of fluid retention, other signs may include difficult breathing, lethargy, bulging eyes, diarrhea and weakness. After listing all these symptoms, one can still find PH cattle lying dead, having had no symptoms at all.
Out of all mammals, cattle are the most likely to contract PH. According to Dr. David Smith, University of Nebraska-Lincoln (UNL) Extension veterinarian, younger, faster-growing cattle are more at risk than mature or lower-performing stock. Obesity and lack of conditioning to altitude as well as a history of pneumonia or heart disease are detrimental. Cold temperatures (below 32° F) are hard on cattle, and, most surprisingly, feeding ionophores can also increase trouble.
What does this have to do with us?
Brisket disease is creeping down to lower elevations. Specifically, it is becoming more common in Nebraska feedlots, especially in the panhandle, where the elevation is just below 4,000 feet. The Nebraska problem was first documented in 1975.
Dr. Smith says a death loss of 2 percent from PH alone is likely in a panhandle feedyard. This is similar to mortality rates with cattle living in high altitudes. The Merck Veterinary Manual indicates 3-5 percent is common in high mountain ranges. Additionally, PH-related death loss has doubled in feedlot cattle over the last decade. Dr. Bob Hough, in a July 2018 Western Livestock Journal article, said losses are coming at the end of the feeding period, when animals are close to ready for harvest.
Why do we see more?
There are two important factors that figure into the increasing feedlot problem. One is the additional weight the industry is currently targeting for fed cattle. Cheap gains, efficient cattle and an acceptance of heavier carcasses line up to make a fed animal far larger than only a few years ago. According to Hough, increased carcass weight is being supported by relatively stable-sized organs. Lung capacity becomes proportionally smaller in relationship to body weight, stressing organs and increasing the risk of PH.
Second, genetics is becoming a larger factor in PH deaths since the advent of successful branded-beef programs. The industry is using ever-increasing numbers of straight-bred British cattle, which were developed at low elevations. The decrease of heterosis, along with heavier fed weights, is helping increase the number of PH deaths.
The susceptibility to PH is, indeed, highly heritable. It is a complex trait influenced by a large number of genes. Pulmonary arterial pressure (PAP) is being studied at the University of Wyoming and Colorado State University (CSU). CSU has determined that PAP’s heritability is greater than heritability for weaning and yearling weights. That’s an amazing discovery, considering the repercussions of PH.
The good news is, there is a push to develop an EPD for susceptibility to PH.
Finding a solution
With an increasing number of fed cattle that are straight-bred Angus, the American Angus Association has been working with CSU to develop calculations for a PAP EPD.
PAP tests are available and highly recommended for bull buyers running cows in high altitude areas.
Tim Holt, a CSU veterinarian, says tests are ideally done at a minimum of one year of age on cattle that have spent three to six weeks at 6,500 feet elevations. A catheter is inserted into the jugular vein, threaded into the heart’s right ventricle and into the main pulmonary artery. A score lower than 41 is considered acceptable. Of course, it is recommended that high-scoring animals not be used for breeding stock.
Because PH is a somewhat localized problem, federal research grant coordinators have been reluctant to fund studies, slowing progress in solving this growing dilemma.
Elimination of expanding diseases may never totally come about, but we can be grateful for private businesses, breed associations, educational and research institutions that never give up searching for better health for our nation’s cattle herd.