Chapman, C. K., Extension Livestock Specialist, Utah State University
Garcia, M.D., Extension Beef Specialist-Beef Genomics, Utah State University
Walburger, M.T., Veterinarian, Arrowhead Veterinary Clinic

ABSTRACT

This study evaluated changes in mean Pulmonary Arterial Pressure (PAP) of bulls enrolled in the Utah Beef Improvement Association’s (UBIA) annual performance tests conducted in accordance with central bull test standards established by the Beef Improvement Federation. Breeds with over 100 bulls tested over the period of 2008 to 2019 were included in the study. Black Angus exhibited significantly higher (P<0.05) mean PAP scores compared to all other breeds.  Red Angus mean scores were also significantly higher than Hereford, but similar to Simmental. Red Angus also showed significantly higher mean rate of increase compared to the other three breeds in the study.

Introduction

The Utah Beef Improvement Association (UBIA) has been conducting an annual bull performance test since 1972. The test has been conducted in cooperation with Utah State University Extension and commercial feedlots to house and feed the bulls. In the 33-year period from 1987 to 2020, the UBIA has tested more than 7,700 bulls and sold more than 3,000 high-performance bulls for use in commercial and purebred herds throughout the western U.S. through the UBIA Performance Bull Test sales.

The primary objective of the test is to assist cattle producers in obtaining genetically-superior, performance-tested bulls that are structurally and reproductively sound. To this end, the UBIA has followed the standards set forth for central bull tests established by the Beef Improvement Federation (BIF, 2016). Allowing the bulls to grow using a primarily forage-based ration, provides them with adequate nutrients to express their genetic differences, while not pushing them so hard that the integrity of their digestive system is compromised.

As the cattle industry has worked to meet consumer demands for higher quality beef eating experiences, the seedstock industry has labored to adapt their cattle to supply the commercial trade with the right type of cattle to meet their needs. This effort has possibly had some collateral side effects not necessarily anticipated during the breeding selection process. This paper will discuss how this effort has impacted Pulmonary Arterial Pressure (PAP) as measured at the conclusion of each testing year of the recent history of the UBIA Performance Test (Test). The objective of the current study is to evaluate and note trends and breed differences over 12 years (2008-2019) of PAP data collected on bulls across the test and between four major breeds enrolled in the test.

Elevated PAP scores can lead to High Altitude Disease aka Brisket Disease in cattle that range at elevations above 7,000 feet, thus the name High Altitude Disease. Calves with high PAP scores are most susceptible to develop swelling throughout the brisket area as the heart works to counteract the effects of hypoxia leading eventually to congestive heart failure. Neary, et.al. (2013) reported that on one Colorado ranch where cattle were raised above 8,000 feet elevation 50% of calves that died between branding and weaning had succumbed to high-altitude disease.

Because PAP is a moderately heritable trait (0.38 +/- 0.07, Shirley, et.al, 2008) , testing prospective herd sires is one of the best ways for a producer to ensure the disease potential of the herd remains low. However, this must be accompanied by culling cows whose calves exhibit susceptibility as Neary, et.al. (2013) stated that the ranch referred to above had been using low PAP bulls in their bull battery for 20 years prior to the study.

PAP testing has become increasingly important not only to cattle producers who run cattle at high altitudes, but also for feedlot operators who are observing higher numbers of cattle on feed that exhibit symptoms of brisket disease at elevations down to 3,000 feet. Neary et.al. (2015) reported that their study in 2012 had shown that 15 of every 10,000 cattle entering U.S. feedlots died of Right Heart Failure (RHF) (a more clinical description of brisket disease), while Jensen, et.al. (1976) reported only 3 cases per 10,000 in four feedlots they studied at an elevation of 5,000’ ft. While these two studies were quite different, they do suggest a definite upward trend in cattle deaths due to brisket disease at elevations much lower than the 7,000 ft. traditionally thought of as the lower boundary for the disease to be exhibited.

This problem is exacerbated given that most of the cattle exhibiting symptoms in feedlots die within a month of harvest, leading researchers to hypothesize that onset of symptoms leading to these losses may be correlated to body weight and condition, similar to coronary disease in humans. Unfortuneately, this scenario leads to the maximum dollar loss for feeders possible because most of the feeding expense has been incurred by that point in the feeding cycle with no return to investment.

Researchers are also trying to determine if there may be other underlying factors that are contributing to the onset of RHF, such as pneumonia and other respiratory diseases (Neary, et.al., 2015). Research is on-going to better understand completely the causes of RHF in these low-elevation situations.

Materials and Methods

Experimental Animals

Beef bulls from any registered breed association have been allowed to participate in the test. Bulls are received annually at the test feedlot in early October. Bulls were divided into two divisions. Junior division included bulls born from January 1 to March 30 of the current calendar year. Senior division included bulls born the previous fall (September through December).

Bull Test Procedures

A series of recommended best management practices were provided to bull owners to reduce management disparities prior to the test.  Once bulls arrived at the test station, all bulls were treated the same relative to warm-up period, booster vaccinations, treatment for parasites, feeding regime and post-test procedures such as ultrasound scanning, PAP testing and breeding soundness evaluation.

PAP Collection Procedure

The PAP readings were collected after the conclusion of the performance test and just prior to conducting the breeding soundness examination. A total of 1372 bulls had PAP scores collected from 2008-2019. The PAP reading was taken using the following procedure as outlined by Holt and Callan (2007).

The bull was secured in a hydraulic squeeze chute with a scissor-type head catch. Once the head was secured, a rope halter was used to pull the head to the side with the nose approximately level with the point of the shoulder to expose the jugular furrow. The jugular furrow was then scrubbed using a chlorhexidine solution.

After cleaning the jugular furrow, a 3.5” 13 gauge needle was used to perforate the jugular until blood was flowing from the needle. The needle was gently threaded down the jugular until only about 1 cm was protruding from the skin. A 1.7 mm, saline-filled, polyethylene catheter attached to an oscilloscope via a pressure transducer that converts the fluid pressure in the catheter into electric signals was used to facilitate collecting the pressure reading. Once the needle was in the correct position, the catheter was inserted into the barrel of the needle and gently threaded down the jugular, into the right atrium of the heart then on into the right ventricle and finally through the pulmonary valve into the pulmonary artery where the pressure reading was taken following an approximate 10-second pause for the pressure to stabilize.

Following removal of the needle and catheter, both went through a disinfecting protocol which included first being rinsed in a povidone iodine solution followed by a chlorhexidine soap and water solution, then rinsed in a chlorhexidine solution and finally allowed to sit in a hot chlorhexidine/isopropyl alcohol solution for at least 5-10 minutes before being ready to be reused. Accordingly, multiple needles and catheters were used daily through the data collection process.

Holt and Callan recommend that PAP readings be collected at elevations above 5,000 feet. PAP readings for the subject animals in the current study were collected at an altitude of 5,315 feet elevation above sea level.

Statistical Analyses

Utilizing the Mixed Model procedures of SAS (version 9.4, SAS Institute, Cary, NC), changes in pulmonary arterial pressure (PAP) for bulls participating in Utah Beef Improvement Association (UBIA) Bull Test from 2008 to 2019 were evaluated.  PAP scores were fit as random variables in the model and year and breed fit as fixed variables. The LSMEANS function, along with the pre-planned pairwise comparisons procedure was utilized to evaluate if significant differences existed between breeds for PAP score means, over the entire testing period from 2008-2019.

Breeds with greater than 100 bulls evaluated were included in the statistical analyses. These included Black Angus, Hereford, Red Angus, and the Simmental breeds. Interval regression analyses as described by Steele et al. (1997) were conducted to determine if the mean rates of change in PAP scores between breeds was significantly different.

Results and Discussion

Least square means analyses revealed significant differences among the four most tested breeds for overall PAP score mean from 2008-2019 (Table 1). The Angus breed had a significantly (P < 0.05) higher overall PAP score mean when compared to all other breeds evaluated. The Red Angus breed also had a significantly higher overall PAP mean score than the Hereford breed but was not significantly different from the Simmental breed. Although significant differences were detected amongst multiple breeds there was not a significant difference when comparing overall means between the Hereford and Simmental breeds. The fact that the Angus breed had the highest PAP score means may be a byproduct of some seedstock AI strategies that incorporated highly desirable bulls from lower elevations into breeding schemes. Furthermore, when evaluating change of PAP among all breeds (Figure 1), PAP scores increased at a rate of 0.81 mmHg per year. While the Angus breed had the highest overall mean, it would be easy to say that the Angus breed was driving this increase in mean PAP scores across the test. However, interval regressions were conducted comparing all breeds to determine if any breed's PAP scores were increasing at a more rapid pace.

Table 1. LSMEANS estimate comparisons between breeds for PAP score means from 2008-2019

BREED	AVERAGE PAP SCORE 2008-2019
Black Angus	39.23a
Hereford	35.92b
Red Angus	38.06c
Simmental	37.12b,c

^*Differing superscripts indicate a difference of means of P < 0.05.

Figure 1. Mean pulmonary arterial pressure (PAP) across all breeds evaluated from 2008-2019. (x axis=year; y axis=mmHg)

Interval regression analyses that evaluated mean rate of change (slope) for PAP scores between breeds from 2008-2019 (Figure 2) revealed that one breed in particular was increasing at a more rapid pace when compared to other breeds. Specifically, the Red Angus breed has increased PAP scores at a significantly higher rate (P < 0.05) than all other breeds. Furthermore, rate of change was not significantly different when comparing the three aforementioned breeds. While the Angus breed may have had the highest overall PAP average over the evaluated time period, its rate of change was similar when compared to the Hereford and Simmental breed who had significantly lower PAP averages over the same time period.

Figure 2.  Rate of change in pulmonary arterial pressure between major breeds evaluated from 2008-2019.  (x axis=year; y axis=mmHg)

Holt and Callan (2007), Neary, et.al. (2013) and Neary et.al. (2015) all indicate that elevated PAP in cattle is a primary causative factor in calf mortality due to High Altitude Disease in calves at elevations above 7,000' and is a possible contributing factor to mortality in feedlot cattle at lower elevations due to RHF. Additional research is currently ongoing to further study the exact causation of RHF in low elevation feedlot cattle.

Conclusion

There have been increases in PAP scores across all breeds examined in this study. Black Angus showed the highest average PAP score over the test period at 39.23 mmHg, which was significantly higher than the other three breeds in the study. Red Angus experienced the greatest rate of change amongst the four breeds in the study at 1.23 mmHg increase annually over the study period. By continuing to conduct PAP testing in conjunction with the bull performance test, the UBIA bull producers are assisting cattle producers in the Intermountain region in securing bulls that meet the needs of their rangeland production systems and that will benefit all segments of the cattle industry as their progeny enter into the production chain.

Additional research needs to be conducted to more fully understand all of the factors associated with the observed increases in PAP and the effects in morbidity and mortality in the beef cattle industry.

Literature Cited

1. Beef Improvement Federation 2016. Guidelines For Uniform Beef Improvement Programs. pp. 49-52  https://beefimprovement.org/wp-content/uploads/2013/07/BIFGuidelinesFinal_updated0916.pdf   Accessed January 15, 2020.

2. Holt, T.N., and R.J. Callan. 2007. Pulmonary Arterial Pressure Testing for High Mountain Disease in Cattle. Vet. Clin. Food Anim. 23 (2007) 575-596. http://csu-cvmbs.colostate.edu/Documents/ilm-pulmonary-arterial-pressure-testing-for-high-mountain-disease-in-cattle.pdf  Accessed September 1, 2020.

3. Jensen, R., R.E. Pierson, P.M. Braddy, D.A. Saari, A. Benitez, D.P. Horton, L.H. Lauerman, A.E. McChesney, A.F. Alexander and D.H. Will. 1976. J. Am Vet Med A 169(5): 515-517.

4. Neary, J.M., D.H. Gould, F.B. Garry, A.P. Knight, D.A. Dargatz, and T.N. Holt. 2013. An Investigation into Beef Calf Mortality on Five High-altitude Ranches that Selected Sires with Low Pulmonary Arterial Pressures for over 20 Years. J. Vet. Diag. Inv. 25(2) 210-218.

5. Neary, J.M., F.B. Garry, T.N. Holt, G.M. Krafsur, P.S. Morley, R.D. Brown, K.R. Stenmark, R.M. Enns and M.G. Thomas. 2015. High Altitude Disease, PAP, Feedlot Hypertension, and Respiratory Issues. Proceedings of the 26^th Range Beef Cow Symposium. November 17-19, 2015. Loveland, Colorado. PP. 141-146.

6. Shirley, K.L, D.W. Beckham and D.J. Garrick, 2008. Inheritance of Pulmonary Arterial Pressure in Angus Cattle and its Correlation with Growth. J. Anim. Sci. 2008. 86:815-819.  https://doi.org/10.2527/jas.2007-0270  Accessed November 9, 2020.

7. Steele, R., J. Torrie, and D. Dickey. 1997. Analysis of covariance. Principles and procedures of statistics: A Biometrical Approach. 3rd edition, McGraw Hill, Inc. New York, NY. 447-449.

    

    

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