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. 2023 Sep 12;101:skad288. doi: 10.1093/jas/skad288

Genetic parameters for pulmonary arterial pressure, yearling performance, and carcass ultrasound traits in Angus cattle

Rachel C Pauling 1, Scott E Speidel 2, Milton G Thomas 3, Timothy N Holt 4, R Mark Enns 5,✉
PMCID: PMC10563144  PMID: 37698445

Abstract

Pulmonary arterial pressure (PAP) can be used as an indicator of susceptibility to pulmonary hypertension and subsequent potential to develop right-sided heart failure (RHF). Previously reported heritability estimates of PAP have been moderate to high. Based on these estimates, selection for the indicator trait, PAP, could reduce the incidence of RHF due to hypoxia. Previous studies have also speculated that increased growth rates and body fat accumulation contribute to increased PAP and RHF. Research evaluating the genetic relationships between PAP and performance traits (e.g., yearling weight and postweaning gain) has yielded conflicting results, leading to ambiguity and uncertainty regarding the underlying genetic relationships. Additionally, no previous research has evaluated the relationship between PAP and ultrasound carcass traits. Therefore, the objective of this study was to estimate trait heritabilities and genetic correlations between PAP, post-weaning growth traits, and ultrasound carcass traits in Angus cattle, using data (n = 4,511) from the American Angus Association. We hypothesized that traits associated with increased growth and muscle would have a positive genetic (i.e., unfavorable) relationship with PAP. Estimates for heritability and genetic correlations were obtained using a multi-trait animal model. Heritability estimates for PAP (0.21 ± 0.04), post-weaning gain (PWG; 0.31 ± 0.04), and yearling weight (YWT; 0.37 ± 0.04) were within the range of estimates previously reported. Genetic correlations were weak (< 0.20) between PAP, PWG, and YWT. A low-to-moderate genetic correlation between PAP and ultrasound ribeye area (UREA) was found (0.25 ± 0.12). Genetic correlations between PAP, ultrasound back fat (UBF), ultrasound intramuscular fat (IMF), and ultrasound rump fat (RUMP) were weak (ranging in magnitude from −0.05 to 0.10) and therefore, do not provide strong support for the hypothesis of an antagonistic relationship between PAP and carcass ultrasound traits, while heritability estimates for UBF (0.43 ± 0.05), UREA (0.31 ± 0.04), IMF (0.35 ± 0.04), and RUMP (0.47 ± 0.05) were in the range of previously reported values.

Keywords: Angus cattle, genetic correlation, growth, heritability, pulmonary arterial pressure, ultrasound

The relationships of pulmonary arterial pressure with growth and carcass traits are relatively small excepting ribeye area where a moderate, unfavorable genetic relationship exists. Therefore, selection decisions should consider pulmonary arterial pressure in a multi-trait approach to beef cattle genetic improvement.

Introduction

Right-side heart failure (RHF) due to hypoxia-induced pulmonary hypertension (PH) is a disease that has commonly affected beef cattle located in mountainous regions with pulmonary arterial pressure (PAP) measures used to indicate the presence and severity of PH. Since the indicator trait, PAP, is moderately heritable (0.20 to 0.46; Enns et al., 1992; Crawford et al., 2016; Pauling et al., 2018), high altitude beef producers commonly include PAP and/or PAP EPD as part of their breeding objective to decrease the incidence of RHF in their herd. However, current reports indicate that heart failure is becoming increasingly problematic in feedlot cattle not located at high elevations, with speculation that high growth rates and body fat accumulation may also contribute to increased incidence of heart-related morbidity and mortality (Neary et al., 2016; Thomas et al., 2018; Krafsur et al., 2019). Concomitantly, increased growth and carcass quality have been major selection criteria in Angus cattle for the last 4 decades (American Angus Association, 2021b); therefore, estimating the genetic relationships of growth and carcass characteristics with PAP is warranted.

Studies evaluating the genetic relationships between growth traits and PAP are limited, and no previous research has evaluated the association between PAP and carcass ultrasound traits. Shirley et al. (2008) reported moderate genetic correlations between PAP measured at weaning and birth weight and weaning weight direct at 0.49 ± 0.12 and 0.51 ± 0.18, respectively. Crawford et al. (2016) also reported a moderate genetic correlation between PAP and WW direct of 0.22 ± 0.08. These studies suggested that there is an unfavorable relationship between growth traits and PAP, but other than for yearling weight (YWT), provided no information on other post-weaning and ultrasound carcass traits. Therefore, the objective of this study was to determine the genetic relationships between PAP and performance traits, including YWT, post-weaning gain (PWG), as well as ultrasound carcass traits, including; back fat (UBF), ribeye area (UREA), percent intramuscular fat (IMF), and rump fat (RUMP). Our hypothesis was that traits associated with increased growth and muscle would have an unfavorable relationship with PAP.

Materials and Methods

Animal Care and Use Committee approval was not obtained for this study because data were obtained from an existing historical database.

Data Summary

Growth, carcass ultrasound, and PAP records on seedstock replacement bulls and heifers were obtained from the American Angus Association (AAA; St. Joseph, MO) with records from registered Angus cattle born between 1992 and 2015. The initial data contained cattle that were PAP tested between 188 and 3,482 d of age; however, only cattle with PAP observations collected between 270 and 720 d of age were used in this study. This age range was utilized so as to include cattle that had a fully developed cardiopulmonary system but not cattle that potentially could be experiencing age induced pulmonary arterial remodeling, as suggested by Neary et al. (2015). After applying data requirements, the mean age of animals at PAP measurement was 452 ± 94 d. A 3-generation pedigree was formed from the constructed data file (n = 4,511), resulting in a pedigree containing 15,296 animals, with 2,024 unique sires and 8,326 unique dams.

Contemporary group (CG) for PAP was defined as a combination of herd, PAP date, and yearling date resulting in 111 unique groups with an average of 41 individuals. Yearling CG was defined as yearling herd, yearling date, yearling management group, and sex. The yearling CG ­designation was also used in the evaluation of post-weaning gain. Carcass ultrasound CG was defined as yearling CG and ultrasound date. Contemporary groups containing offspring of a single sire or CG’s with no phenotypic variance were excluded from the analyses. The age of dam of animals was classified following recommendations of the Beef Improvement Federation (BIF, 2010). Performance and PAP records used for these analyses are summarized in Table 1.

Table 1.

Descriptive statistics of mean pulmonary arterial pressure (PAP), yearling weight (YWT), post-weaning gain (PWG), ultrasound back fat (UBF), ultrasound ribeye area (UREA), ultrasound intramuscular fat (IMF), ultrasound rump fat (RUMP) from the American Angus Association classified by animal sex

Item n Minimum Mean Maximum SD
PAP, mmHg 4,511 30 43.3 180 10.72
 Bull 3,711 30 43.9 180 11.4
 Heifer 800 32 40.4 115 5.7
YWT, kg 4,511 222 447 658 68.19
 Bull 3,711 283 465 658 56.86
 Heifer 800 222 362 510 48.73
PWG, kg 4,491 39 167 344 60.04
 Bull 3,692 43 184 344 49.93
 Heifer 799 3 89 209 36.64
UBF, mm 3,688 1.02 4.71 15.24 2.27
 Bull 3,201 1.02 4.75 15.24 2.28
 Heifer 487 1.02 4.43 14.99 2.18
UREA, cm2 3,685 29.03 72.58 105.81 11.50
 Bull 3,201 46.45 75.32 105.81 9.14
 Heifer 484 29.03 54.48 83.23 8.77
IMF, % 3,685 1.05 3.37 9.54 0.92
 Bull 3,201 1.05 3.26 9.54 0.88
 Heifer 484 1.63 4.05 7.66 0.88
RUMP, mm 3,690 1.02 5.36 17.02 2.64
 Bull 3,201 1.02 5.40 17.02 2.59
 Heifer 489 1.02 5.09 16.76 2.93
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Statistical Analysis

Data used in this project were analyzed using the statistical software package ASREML 3.0 (Gilmour et al., 2009). Two separate 6-trait analyses were performed to determine heritabilities and genetic correlations. First, PAP was evaluated in a model containing the ultrasound carcass traits UBF, UREA, IMF, along with YWT. Second, PAP and the ultrasound traits were evaluated with PWG. The distinction between the use of YWT versus PWG was to determine the genetic relationships between body weight at a year of age, the age at which PAP is typically measured in breeding cattle, and also growth rate. This manuscript focuses on post-weaning traits (i.e., YWT and ultrasound carcass measures) given that these traits are often measured at similar or nearly similar ages leading seedstock breeders to question the relationship.

The general form of the 6-trait animal model used in both analyses is as follows:

[y1y2y3y4y5y6]=[X1000000X2000000X3000000X4000000X5000000X6][b1b2b3b4b5b6]+[Z1000000Z2000000Z3000000Z4000000Z5000000Z6][u1u2u3u4u5u6]+[e1e2e3e4e5e6]

In the above equation, yi is a vector of observations for PAP, UBF, UREA, IMF, RUMP, and YWT or PWG, Xi is a known incidence matrix relating unknown fixed effects in bi to observations in y, Zi is incidence matrices relating unknown random direct genetic effects in ui to observations in y, and ei is a vector of random residual errors specific to each observation.

As mentioned above, random effects were assumed to have means of 0 and variances represented as

var [ue]= [G ⊗A00R ⊗ In ]

G is the additive genetic (co)variance matrix, A is Wright’s numerator relationship matrix, R is the residual (co)­variance matrices for traits, and In is an identity matrix whose order was equal to the number of observations for each of the traits.

Fixed effects included for each trait are shown in Table 2. All fixed effects included in the evaluations were found to account for a significant amount of variability in their respective dependent variables (P < 0.05) based on Wald F statistics.

Table 2.

Fixed and random effects included in the multi-trait animal model for mean pulmonary arterial pressure, ultrasound back fat, ultrasound ribeye area, ultrasound intramuscular fat, and ultrasound rump fat from American Angus Association data

Effect1 Model YWT1 PWG1
PAP1 UBF1 UREA1 IMF1 RUMP1
Fixed
 Age (d) X X X X X X
 Age of dam2 X X
 Sex X
 PAPCG3 X
 USNDCG4 X X X X
 YWCG5 X X
Random
 Direct additive X X X X X X X
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1PAP, mean pulmonary arterial pressure; UBF, ultrasound back fat; UREA, ultrasound ribeye area; IMF, ultrasound intramuscular fat; RUMP, ultrasound rump fat; YWT, yearling weight; PWG, post-weaning gain.

2Age of dam represents the Beef Improvement Federation Age of Dam Categories.

3Pulmonary arterial pressure contemporary group (PAPCG) = PAP date, herd, and yearling date.

4Carcass ultrasound contemporary group (USNDCG) = yearling weight contemporary group and ultrasound date.

5Yearling weight contemporary group (YWCG) = yearling herd, yearling date, yearling management group, sex.

Results and Discussion

Multi-Trait Analyses of PAP and Growth Traits

The two multi-trait analyses of PAP, growth, and ultrasound traits provided heritability estimates for each trait as well as genetic correlations between the traits. Results from the multi-trait analysis of PAP, ultrasound, and YWT are displayed in Table 3.

Table 3.

Heritabilities (diagonal; SE), genetic correlations (above diagonal; SE), and residual correlations (below diagonal; SE) from the 6-trait model for mean pulmonary arterial pressure (PAP), back fat (UBF), ribeye area (UREA), intramuscular fat (IMF), rump fat (RUMP), and yearling weight (YWT)

Trait1 PAP UBF UREA IMF RUMP YWT
PAP 0.21 (0.04) −0.02 (0.12) 0.25 (0.12) −0.05 (0.12) 0.10 (0.11) 0.01 (0.11)
UBF −0.06 (0.04) 0.43 (0.05) 0.15 (0.10) 0.08 (0.10) 0.70 (0.05) 0.22 (0.09)
UREA −0.19 (0.04) 0.18 (0.04) 0.31 (0.04) −0.31 (0.10) −0.07 (0.10) 0.23 (0.10)
IMF 0.04 (0.04) 0.29 (0.04) 0.03 (0.04) 0.35 (0.04) 0.12 (0.09) 0.23 (0.09)
RUMP −0.10 (0.04) 0.51 (0.04) 0.27 (0.05) 0.22 (0.05) 0.47 (0.05) 0.15 (0.09)
YWT −0.06 (0.04) −0.05 (0.04) 0.52 (0.03) 0.17 (0.04) 0.35 (0.05) 0.37 (0.04)
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In this analysis, the genetic correlation was found to be low (<0.20) between PAP, YWT, and PWG. These low values suggested that selection for increased growth rate and decreased PAP values should be possible given the appropriate selection tools (i.e., EPD for PAP in addition to already available YWT EPD) despite the genetic relationship being unfavorable. The magnitude of the genetic correlation herein is less than those between BW and YWT (American Angus Association, 2021a), where genetic trends indicate the potential to identify animals with low BW and high YWT (American Angus Association, 2021b) which would indicate the same potential for improvement in PAP. The heritability estimate for PAP was 0.22 ± 0.04, which was within the range of recently reported heritability estimates in Angus cattle (0.20 to 0.46; Enns et al., 1992; Shirley et al., 2008; Cockrum et al., 2014; Crawford et al., 2016). Heritability estimates for all growth traits were found to be within the range of previously reported literature as well (Arnold et al., 1991; Gregory et al, 1995; Shirley et al., 2008; Crawford et al., 2016).

Results from the multi-trait analysis of PAP, the ultrasound carcass traits, and PWG are shown in Table 4. Heritability and genetic correlation estimates of PAP were similar to the estimates obtained from the multi-trait model that included YWT. The heritability estimate for PWG (0.31 ± 0.04) was within the range of previously reported estimates in Angus, Hereford, and composite cattle (Schimmel, 1982; Bennett et al., 1996; Crawford et al., 2016). There was a minimal genetic correlation between PAP and PWG (−0.11 ± 0.12) with an application of the standard error resulting in a range that included 0. This supports previous findings by Crawford et al. (2016), which reported an estimate of −0.10 ± 0.10.

Table 4.

Heritabilities (diagonal; SE), genetic correlations (above diagonal; SE) and residual correlations (below diagonal; SE) from the 6-trait model for mean pulmonary arterial pressure (PAP), back fat (UBF), ribeye area (UREA), intramuscular fat (IMF), rump fat (RUMP), and post-weaning gain (PWG)

Trait PAP UBF UREA IMF RUMP PWG
PAP 0.21 (0.04) −0.04 (0.12) 0.24 (0.12) −0.05 (0.12) 0.09 (0.11) −0.11 (0.12)
UBF −0.06 (0.04) 0.42 (0.05) 0.12 (0.10) 0.07 (0.10) 0.70 (0.05) 0.26 (0.10)
UREA −0.19 (0.04) 0.19 (0.04) 0.30 (0.04) −0.33 (0.10) −0.08 (0.10) 0.20 (0.10)
IMF 0.04 (0.04) 0.29 (0.04) 0.04 (0.04) 0.35 (0.04) 0.11 (0.09) −0.12 (0.11)
RUMP −0.11 (0.04) 0.52 (0.04) 0.27 (0.05) 0.22 (0.05) 0.47 (0.05) 0.19 (0.10)
PWG −0.07 (0.04) 0.28 (0.04) 0.38 (0.04) 0.15 (0.04) 0.30 (0.04) 0.31 (0.04)
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Multi-Trait Analysis of PAP and Carcass Ultrasound Traits

Heritability and genetic correlation estimates for PAP and carcass ultrasound traits are displayed in Tables 3 and 4. A moderate, positive, genetic correlation of 0.25 ± 0.12 was estimated between PAP and UREA. This relationship is likely the most concerning between PAP and the ultrasound traits as it suggests an unfavorable correlated response to selection. Yet, the magnitude of the relationship is less than that of BW and WW or PWG in the AAA population (American Angus Association, 2021a) where selection has managed to overcome the unfavorable relationships as illustrated by genetic trends in that population. Genetic correlations between PAP, UBF, IMF, and RUMP fat were low (<0.20) and therefore selection for these production traits would likely cause little change in PAP. The heritability estimate for PAP (0.21 ± 0.04) was found to be within the range (0.20 to 0.46) of previous reports in Angus cattle (Enns et al., 1992; Shirley et al., 2008; Crawford, et al., 2016; Pauling et al., 2018). Similarly, heritability estimates for carcass ultrasound traits were all found to be within the range of previously reported literature in Angus, Hereford, and crossbred beef cattle (Arnold et al., 1991; Robinson et al., 1993; Reverter et al., 2000; Arthur et al., 2001; Su et al., 2016).

A previously suggested hypothesis was that increases in muscle mass and fat deposition may lead to increased PAP (Jensen et al., 1976; Neary et al., 2015); however, the genetic relationship between these traits has not been previously evaluated. The moderate genetic correlation between PAP and UREA (0.25 ± 0.12) reported in this study supports that hypothesis—that increased muscle mass is correlated with increased PAP. This also supports previous research by Lekeux et al. (1994), which suggested that Belgian Blue cattle, a “double-muscled” breed, were more susceptible to hypoxemia than other cattle breeds. As selection and breed improvement programs are developed and more PAP data become available, this relationship should be re-estimated, but for now, breeders should recognize the unfavorable genetic relationship.

Results from this study revealed a minimal genetic relationship between PAP and fat deposition traits. However, in comparison, studies in humans have suggested that increased levels of obesity are associated with increased blood pressure, with a 10 kg increase in body weight corresponding to a 12% increase in the risk of heart disease (Hall, 2003; Poirier et al., 2006, Gobbo et al., 2015). Feedlot cattle are typically fed a high-concentrate diet to promote increased growth rates and increased fat; however, this study only utilized ultrasound data from bulls and heifers, likely yearling animals destined for use as herd replacement animals, and generally, these cattle are managed in such a way as to limit excessive fat deposition. Therefore, these cattle are on a different growth curve trajectory than the fattened steers described as suffering from feedlot heart disease (Neary et al., 2016, Thomas et al., 2018; Krafsur et al., 2019). However, the knowledge of this relationship, may reduce concerns associated with selection for increased fat deposition and increases in UBF, RUMP, or UIMF to also result in cattle more likely to suffer from pulmonary hypertension.

The results from the multi-trait analyses of PAP, growth traits, and carcass ultrasound traits support our hypothesis that increased growth and muscle mass are genetically correlated to increased PAP observations in Angus cattle. There appeared to be no significant genetic correlations between PAP, YWT, PWG, UBF, IMF, or RUMP typically measured on replacement bulls and heifers.

This information is important for beef producers to consider when making selection decisions, especially for cattle located at high elevations. Information is also useful for directing the improvement of the Angus breed. Profitability in the beef industry is primarily driven by live animal weight and/or carcass quality and traits associated with costs of production. Continual selection for improvement in these traits could inadvertently be increasing metabolic oxygen demands beyond the capability of the bovine cardiopulmonary system; however, this study suggested that at the genetic level, those risks are slight and primarily associated with increases in UREA.

Acknowledgments

The authors thank the American Angus Association for supplying the data used in this study and for the financial support of the project. We also thank Dr. Timothy Holt for supplying data, as well as Colorado State University’s John E. Rouse Endowments and its Beef Improvement Center for also supplying data as well as financial support of graduate students and faculty. This project was also partially supported by Hatch Project Accession Number 1010007 from the USDA National Institute of Food and Agriculture for support of faculty at Colorado State University.

Glossary

Abbreviations

AAA

American Angus Association

BWT

birth weight

CG

contemporary group

IMF

ultrasound percent intramuscular fat

PAP

pulmonary arterial pressure

PH

pulmonary hypertension

PWG

post-weaning gain

RHF

right-side heart failure

RUMP

rump fat

UBF

ultrasound back fat

UREA

ultrasound ribeye area

WWT

weaning weight

YWT

yearling weight

Contributor Information

Rachel C Pauling, Department of Animal Sciences, Colorado State University Fort Collins, CO 80523, USA.

Scott E Speidel, Department of Animal Sciences, Colorado State University Fort Collins, CO 80523, USA.

Milton G Thomas, Department of Animal Sciences, Texas A&M AgriLife Research, Beeville, TX 78102, USA.

Timothy N Holt, Department of Clinical Sciences, Colorado State University, Fort Collins, CO 80523, USA.

R Mark Enns, Department of Animal Sciences, Colorado State University Fort Collins, CO 80523, USA.

Conflict of Interest Statement

The authors declare no conflict of interest.

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