Heritabilities and genetic correlations of pulmonary arterial pressure and performance traits in Angus cattle at high altitude

The Use of Pulmonary Arterial Pressure (PAP) for Improved Beef Cattle Management

Pulmonary arterial pressure (PAP) determines cattle's susceptibility to High Altitude Disease (HAD), also known as Brisket Disease, High Mountain Disease, and right-sided heart failure (RHF). This non-infectious disease causes pulmonary hypertension due to hypoxia. PAP measures the resistance of blood flow through the lungs. It is estimated that 1.5 million head of cattle are raised in high-altitude environments (above 1500 m), and HAD accounts for 3-5% of calf death loss yearly. In addition, there have been increasing concerns about feedlot cattle succumbing to RHF at moderate elevations. This review focuses on the historical background, explanation of PAP measurement and scores, genetic implications, and the relationship between PAP and economically relevant traits. Specifically, traits such as gestation length, birth weight, weaning weight, and yearling weight may impact PAP scores. In addition, environmental effects and other factors impacting PAP score variations are discussed. Information gaps and research needs are addressed to determine where missing information could improve the understanding of PAP while also benefiting beef cattle producers in high-elevation production systems.

Variance component estimates, phenotypic characterization, and genetic evaluation of bovine congestive heart failure in commercial feeder cattle

The increasing incidence of bovine congestive heart failure (BCHF) in feedlot cattle poses a significant challenge to the beef industry from economic loss, reduced performance, and reduced animal welfare attributed to cardiac insufficiency. Changes to cardiac morphology as well as abnormal pulmonary arterial pressure (PAP) in cattle of mostly Angus ancestry have been recently characterized. However, congestive heart failure affecting cattle late in the feeding period has been an increasing problem and tools are needed for the industry to address the rate of mortality in the feedlot for multiple breeds. At harvest, a population of 32,763 commercial fed cattle were phenotyped for cardiac morphology with associated production data collected from feedlot processing to harvest at a single feedlot and packing plant in the Pacific Northwest. A sub-population of 5,001 individuals were selected for low-pass genotyping to estimate variance components and genetic correlations between heart score and the production traits observed during the feeding period. At harvest, the incidence of a heart score of 4 or 5 in this population was approximately 4.14%, indicating a significant proportion of feeder cattle are at risk of cardiac mortality before harvest. Heart scores were also significantly and positively correlated with the percentage Angus ancestry observed by genomic breed percentage analysis. The heritability of heart score measured as a binary (scores 1 and 2 = 0, scores 4 and 5 = 1) trait was 0.356 in this population, which indicates development of a selection tool to reduce the risk of congestive heart failure as an EPD (expected progeny difference) is feasible. Genetic correlations of heart score with growth traits and feed intake were moderate and positive (0.289-0.460). Genetic correlations between heart score and backfat and marbling score were -0.120 and -0.108, respectively. Significant genetic correlation to traits of high economic importance in existing selection indexes explain the increased rate of congestive heart failure observed over time. These results indicate potential to implement heart score observed at harvest as a phenotype under selection in genetic evaluation in order to reduce feedlot mortality due to cardiac insufficiency and improve overall cardiopulmonary health in feeder cattle.

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

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.

Pulmonary arterial pressure in fattened Angus steers at moderate altitude influences early postmortem mitochondria functionality and meat color during retail display

Pulmonary hypertension is a noninfectious disease of cattle at altitudes > 1524 m (5,000 ft). Mean pulmonary arterial pressures (PAP) are used as an indicator for pulmonary hypertension in cattle. High PAP cattle (≥50 mmHg) entering the feedlot at moderate elevations have lower feed efficiency as compared to low PAP cattle (< 50 mmHg). The impact of pulmonary arterial pressure on mitochondrial function, oxidative phosphorylation (OXPHOS) protein abundance, and meat color was examined using longissimus lumborum (LL) from high (98 ± 13 mmHg; n = 5) and low (41 ± 3 mmHg; n = 6) PAP fattened Angus steers (live weight of 588 ± 38 kg) during early postmortem period (2 and 48 h) and retail display (days 1 to 9), respectively. High PAP muscle had greater (P = 0.013) OXPHOS-linked respiration and proton leak-associated respiration than low PAP muscles at 2 h postmortem but rapidly declined to be similar (P = 0.145) to low PAP muscle by 48 h postmortem. OXPHOS protein expression was higher (P = 0.045) in low PAP than high PAP muscle. During retail display, redness, chroma, hue, ratio of reflectance at 630 and 580 nm, and metmyoglobin reducing activity decreased faster (P < 0.05) in high PAP steaks than low PAP. Lipid oxidation significantly increased (P < 0.05) in high PAP steaks but not (P > 0.05) in low PAP. The results indicated that high PAP caused a lower OXPHOS efficiency and greater fuel oxidation rates under conditions of low ATP demand in premortem beef LL muscle; this could explain the lower feed efficiency in high PAP feedlot cattle compared to low PAP counterparts. Mitochondrial integral function (membrane integrity or/and protein function) declined faster in high PAP than low PAP muscle at early postmortem. LL steaks from high PAP animals had lower color stability than those from the low PAP animals during simulated retail display, which could be partially attributed to the loss of muscle mitochondrial function at early postmortem by ROS damage in high PAP muscle.

ImmuneDEX: a strategy for the genetic improvement of immune competence in Australian Angus cattle

In animal breeding and genetics, the ability to cope with disease, here defined as immune competence (IC), with minimal detriment to growth and fertility is a desired objective which addresses both animal production and welfare considerations. However, defining and objectively measuring IC phenotypes using testing methods which are practical to apply on-farm has been challenging. Based on previously described protocols, we measured both cell-mediated immune response (Cell-IR) and antibody-mediated immune response (Ab-IR) and combined these measures to determine an animal's IC. Using a population of 2,853 Australian Angus steers and heifers, we compared 2 alternative methods to combine both metrics into a single phenotype to be used as a tool for the genetic improvement of IC. The first method, named ZMEAN, is obtained by taking the average of the individual metrics after subjecting each to a Z-score standardization. The second, ImmuneDEX (IDEX), is a weighted average that considers the correlation between Cell-IR and Ab-IR, as well as the difference in ranking of individuals by each metric, and uses these as weights in the averaging. Both simulation and real data were used to understand the behavior of ZMEAN and IDEX. To further ascertain the relationship between IDEX and other traits of economic importance, we evaluated a range of traits related to growth, feedlot performance, and carcass characteristics. We report estimates of heritability of 0.31 ± 0.06 for Cell-IR, 0.42 ± 0.06 for Ab-IR, 0.42 ± 0.06 for ZMEAN and 0.370 ± 0.06 for IDEX, as well as a unity genetic correlation (rg) between ZMEAN and IDEX. While a moderately positive rg was estimated between Cell-IR and Ab-IR (rg = 0.33 ± 0.12), strongly positive estimates were obtained between IDEX and Cell-IR (rg = 0.80 ± 0.05) and between IDEX and Ab-IR (rg = 0.85 ± 0.04). We obtained a moderately negative rg between IC traits and growth including an rg = -0.38 ± 0.14 between IDEX and weaning weight, and negligible with carcass fat measurements, including an rg = -0.03 ± 0.12 between IDEX and marbling. Given that breeding with a sole focus on production might inadvertently increase susceptibility to disease and associated antibiotic use, our analyses suggest that ImmuneDEX will provide a basis to breed animals that are both highly productive and with an enhanced ability to resist disease.

Evaluation of the sensitivity of pulmonary arterial pressure to elevation using a reaction norm model in Angus Cattle

Pulmonary arterial pressure (PAP) is a diagnostic measure used to determine an individual's susceptibility to developing high-altitude disease. The importance of PAP measures collected at elevations lower than the intended breeding elevation of the bulls (i.e., ≥1,520 m) is unknown. Therefore, the objective of this study was to determine the genetic relationship between PAP measures collected in a range of elevations using reaction norm models. A total of 9,177 PAP and elevation observations on purebred Angus cattle, which averaged 43.49 ± 11.32 mmHg and 1,878.6 ± 296.8 m, respectively, were used in the evaluation. The average age of the individuals in the evaluation was 434.04 ± 115.9 d. A random regression model containing the effects of sex, a linear covariate of age, a quadratic fixed covariate of elevation, and random effects consisting of a contemporary group and a linear regression of PAP on elevation was used for the evaluation of PAP. Two forms of PAP were evaluated with this model. First, to address the non-normality of the data, PAP was raised to the power of -2.6 (ptPAP) based on the results of a Box-Cox analysis. Second, raw PAP (rPAP) phenotypes were evaluated to compare the results to those obtained from the transformed data. For ptPAP, heritability ranged from 0.25 to 0.37 corresponding to elevations of 1,900 and 1,215 m, respectively. For rPAP, heritability ranged from 0.22 to 0.41 corresponding to elevations of 1,700 and 2,495 m, respectively. Generally, lower elevations corresponded to decreased heritabilities while higher elevations corresponded to increased heritability estimates. For ptPAP, genetic correlations ranged from 0.18 (elevation: 1,215 and 2,495 m) to 1.00. For rPAP, genetic correlations ranged from 0.08 (elevation: 1,215 and 2,495 m) to 1.00. In general, the closer the elevations in which PAP was measured, the greater the genetic relationship. The greater the difference in elevation between PAP measures resulted in lower genetic correlations. The rank correlation between expected progeny differences (EPD) for 1,215 and 2,495 m was 0.65 and 0.49 for the ptPAP and rPAP, respectively. These results suggested that PAP measures collected in lower elevations may be used as an indicator of high-altitude adaptability. In the estimation of EPD to rank sires for their suitability for use in high-elevation production systems, it is important to account for the relationships among varied altitudes.

Evaluation of moderate to high elevation effects on pulmonary arterial pressure measures in Angus cattle1

Altitude-induced pulmonary hypertension is a disease once thought to only occur at extremely high elevations (>1,600 m), but recently, it has been observed at moderate elevations of 1,200 to 1,600 m. Pulmonary arterial pressure (PAP) has been used as an indicator of tolerance to high altitude in mountainous beef production systems for over 30 yr. The trait is typically measured on yearling bulls and heifers with values ≤ 41 mmHg being favorable. These observations were historically only considered valid when they were recorded at elevations ≥ 1,600 m; however, if observations from lower (i.e., moderate) elevations were reliable indicators, a greater number of cattle records could be used in genetic improvement programs for high-altitude beef systems. The objectives of this study were to evaluate the relationship between PAP and elevation, as well as to determine whether PAP measures obtained at moderate elevations (ME) less than 1,600 m have a genetic relationship with PAP observations obtained at high elevations (HE) 1,600 m or greater. Elevation and PAP data from purebred Angus cattle (n = 14,665) from 349 contemporary groups were used in the analyses. Elevation and PAP averaged 1,887 ± 1.8 m and 43.0 ± 0.1 mm Hg, respectively. A univariate model containing the effects of sex, age, elevation category (HE vs. ME), elevation (continuous), and elevation category by elevation interaction along with a random direct genetic effect was utilized to determine the relationship between PAP and elevation. In this model, all main effects were found to be significant contributors of variation in PAP (P < 0.001). The interaction between elevation category and elevation was not a significant contributor to variability of PAP (P > 0.05). A bivariate animal model was then used to evaluate the relationship between PAP observations obtained between HE and ME groups. Heritability estimates for these 2 groups were 0.34 ± 0.03 and 0.29 ± 0.09, respectively, and their genetic correlation was 0.83 ± 0.15. Even though this is a strong genetic relationship, results of this study support the hypothesis that PAP observations collected at HE and ME are not perfectly, genetically related. Results suggest that PAP measures collected from 1,219 to 1,600 m may be useful as a correlated trait in a multitrait genetic evaluation to produce EPD useful for selection of animals with reduced susceptibility to pulmonary hypertension.

Selection signatures for high-altitude adaptation in ruminants

High-altitude areas are important socio-economical habitats with ruminants serving as a major source of food and commodities for humans. Living at high altitude, however, is extremely challenging, predominantly due to the exposure to hypoxic conditions, but also because of cold temperatures and limited feed for livestock. To survive in high-altitude environments over the long term, ruminants have evolved adaptation strategies, e.g. physiological and morphological modifications, which allow them to cope with these harsh conditions. Identification of such selection signatures in ruminants may contribute to more informed breeding decisions, and thus improved productivity. Moreover, studying the genetic background of altitude adaptation in ruminants provides insights into a common molecular basis across species and thus a better understanding of the physiological basis of this adaptation. In this paper, we review the major effects of high altitude on the mammalian body and highlight some of the most important short-term (coping) and genetically evolved (adaptation) physiological modifications. We then discuss the genetic architecture of altitude adaptation and target genes that show evidence of being under selection based on recent studies in various species, with a focus on ruminants. The yak is presented as an interesting native species that has adapted to the high-altitude regions of Tibet. Finally, we conclude with implications and challenges of selection signature studies on altitude adaptation in general. We found that the number of studies on genetic mechanisms that enable altitude adaptation in ruminants is growing, with a strong focus on identifying selection signatures, and hypothesise that the investigation of genetic data from multiple species and regions will contribute greatly to the understanding of the genetic basis of altitude adaptation.

Successful treatment of suckling Red Angus calves for bovine respiratory disease is not associated with increased mean pulmonary arterial pressures at weaning

The purposes of this study were to determine if the successful treatment of bovine respiratory disease (BRD) in suckling calves was associated with a long-term increase in mean pulmonary arterial pressure (mPAP) and, to screen for associations between blood leukogram variables and mPAP. A cohort of Red Angus calves (n = 74) were followed from birth to weaning at an altitude of 975 m. Calves were weaned at 172 ± 14 d when their mPAP was measured and whole blood collected. Thirty calves that had been treated for BRD (34 to 45 d prior) and 30 calves that had not required treatment for BRD were sampled. Treatment for BRD had no effect on mPAP (P = 0.37). Mean mPAP was 48 ± 8 mm Hg (± SD) with a minimum of 34 mm Hg and a maximum at 69 mm Hg. Weaning weight and sex tended to be associated with mPAP, but they explained just 5% of the variation in mPAP (P = 0.08; Adj. r2 = 0.05). Fibrinogen (P = 0.008) and absolute lymphocyte count (P = 0.06) were negatively associated with mPAP, whereas absolute monocyte count was positively associated with mPAP (P = 0.01). The findings of this study suggest that pre-weaning treatment for BRD does not increase a calves' post-weaning risk of congestive right heart failure. Further, components of the immune and acute phase response system may play a role in the development and progression of pulmonary hypertension.