The problem of pulmonary hypertension and congestive heart failure for cattle at high altitude, as well as market-ready feedlot cattle, continues to be a focus for research. The development of EPDs (expected progeny differences) for the indicator trait pulmonary arterial pressure (PAP) is also progressing. Although the correlation between PAP, pulmonary hypertension, and death loss at high altitude appears to be well understood, its impact on sudden death in market-ready feedlot cattle is still the subject of intense research.
Feedlot congestive heart failure
It is believed, but not scientifically confirmed, that PAP plays a role in pulmonary hypertension and congestive heart failure in market-ready feedlot cattle. The subject is complicated by the number of other factors that could contribute to the death loss. However, preliminary research findings suggest that high PAP feedlot cattle have lower gain, feed conversion, and end product value.
Cattle naturally have a lower ability to oxygenate their body compared to many species, which makes them susceptible to pulmonary hypertension without any stressors. In addition to PAP, there are also a number of other factors that could impact feedlot cattle. This includes any decreased respiratory function, which could occur from things like bovine respiratory disease (BRD) or dust. Near market-ready cattle are also obese, which can result in fat deposits in their hearts. With cattle being taken to heavier weights than in the past, the final gain will disproportionally be in the carcass with organ mass staying relatively constant.
All this adds up to several factors that could result in pulmonary hypertension.
Pulmonary hypertension affects the right side of the heart, but there is some preliminary research that in feedlot cattle, the left side of the heart may also be affected. While Colorado State University has been the clear leader in PAP research, Kansas State University is also building a database of feedlot data on death loss and its necropsy. They are combining this with the collection of genomic data to help sort out the problem.
Although there clearly are a number of factors that could affect congestive heart failure in feedlot cattle, PAP is a prime candidate as one of the leading factors. There also appear to be breed differences in susceptibility to pulmonary hypertension as various breeds were originally developed from the Alps to the lowlands.
Circumstantial evidence suggests the incidence of congestive heart failure increased significantly when the industry started feeding cattle to a higher degree of finish at a younger age, as well as when Angus became the dominate breed. Luckily, if the latter is part of the problem, the American Angus Association is being proactive about objectively characterizing their cattle for PAP.
Generating EPDs
Two entities are at the forefront of producing PAP EPDs: American Angus Association and Leachman Cattle of Colorado. The American Angus Association released its first PAP EPDs in a research run in February 2019. They are collecting data at cutoffs they classify as high elevations (>5,500 feet) and moderate elevation (4,000 to 5,500 feet). Cattle PAP at the higher elevation have considerably higher heritability at 0.36 than at moderate elevation, which is only 0.16 heritability. However, the genetic correlation between the two is over 0.80, which means the moderate elevation data can be used to add accuracy to a genetic prediction based on the higher altitude.
Angus Genetics Incorporated’s (AGI) President Dr. Dan Moser reports that the research EPD has been well received by producers, and reports from producers are that they are lining up with what people are seeing in the field. The EPD is also being calculated utilizing their single-step methodology of genomically enhancing the prediction by providing more knowledge on the relationship between animals.
They are now preparing to release their second research run of PAP EPDs, which is expected in January 2020. They are evaluating including into the model PAP scores from weaned animals, which will add further accuracy to the genetic predictions. If the EPDs are well received, production runs could be as close as June 2020.
Leachman Cattle of Colorado has been producing production runs on PAP EPDs for several years, and they cannot overemphasize their importance when running cattle at altitude. They also recognize its possible impact in feedlot cattle, although, its effect there is not fully understood. They also explain that an individual’s PAP measurement may give an idea as to how an individual will do at elevation, but its EPD is what should be used to evaluate how an animal’s progeny will perform and survive.
Leachman’s takes a different tack on measuring PAP scores in their cattle than American Angus. They feel they get their best quality data on older bulls above 7,000 feet, which has a heritability of over 0.40. They are strong believers that to get the best data, cattle need to be put in an environment to express the trait. They first warm up cattle at approximately 5,200 feet before taking them up to higher elevation where they are eventually tested. One popular sire had three-quarters death loss before moving to the higher elevation, so there are major differences between bloodlines.
In the end, Lee Leachman thinks that when producers are making buying decisions, they need to take a close look at the conditions the cattle were tested for PAP, which means putting more weight scores on older cattle tested at higher elevation. He also emphasizes the need to test females as well as bulls to get a full picture.
Whether a producer runs cattle at high elevation or feeds cattle at more moderate elevation in high plains feedlots, pulmonary hypertension and congestive heart failure is a problem our industry must find solutions to. Although the relationship between PAP and congestive heart failure is not fully understood, at this point, the best indicator trait the industry has are PAP EPDs. Therefore, it is important that the number of breeds producing them expands in the coming years. — Dr. Bob Hough, WLJ correspondent
