Results From the Big Ten COVID-19 Cardiac Registry: Impact of SARS-COV-2 on Myocardial Involvement.

OBJECTIVE: COVID-19 has been associated with myocardial involvement in collegiate athletes. The first report from the Big Ten COVID-19 Cardiac Registry (Registry) was an ecological study that reported myocarditis in 37 of 1597 athletes (2.3%) based on local clinical diagnosis. Our objective was to assess the relationship between athlete and clinical characteristics and myocardial involvement. DESIGN: Cross-sectional study. SETTING: We analyzed data from 1218 COVID-19 positive Big Ten collegiate athletes who provided informed consent to participate in the Registry. PARTICIPANTS: 1218 athletes with a COVID-19-positive PCR test before June 1, 2021. ASSESSMENT OF INDEPENDENT VARIABLES: Demographic and clinical characteristics of athletes were obtained from the medical record. MAIN OUTCOME MEASURES: Myocardial involvement was diagnosed based on local clinical, cardiac magnetic resonance (CMR), electrocardiography, troponin assay, and echocardiography. We assessed the association of clinical factors with myocardial involvement using logistic regression and estimated the area under the receiver operating characteristic (ROC) curve. RESULTS: 25 of 1218 (2.0%) athletes met criteria for myocardial involvement. The logistic regression model used to predict myocardial involvement contained indicator variables for chest pain, new exercise intolerance, abnormal echocardiogram (echo), and abnormal troponin. The area under the ROC curve for these indicators was 0.714. The presence of any of these 4 factors in a collegiate athlete who tested positive for COVID-19 would capture 55.6% of cases. Among noncases without missing data, 86.9% would not be flagged for possible myocardial involvement. CONCLUSION: Myocardial involvement was infrequent. We predicted case status with good specificity but deficient sensitivity. A diagnostic approach for myocardial involvement based exclusively on symptoms would be less sensitive than one based on symptoms, echo, and troponin level evaluations. Abnormality of any of these evaluations would be an indication for CMR.

Invasive Implanted Hemodynamic Monitoring in Patients With Complex Congenital Heart Disease: State-of-the-Art Review.

As the number of patients with congenital heart disease (CHD) continues to increase, the burden of heart failure (HF) in this population requires innovative strategies to individualize management. Given the success of implanted invasive hemodynamic monitoring (IHM) with the CardioMEMSTM HF system in adults with acquired HF, this is often suggested for use in patients with CHD, though published data are limited to case reports and case series. Therefore, this review summarizes the available published reports on the use of IHM in patients with complex CHD, describes novel applications, and highlights future directions for study. In patients with CHD, IHM has been used across the lifespan, from age 3 years to adulthood, with minimal device-related complications reported. IHM uses include (1) prevention of HF hospitalizations; (2) reassessment of hemodynamics after titration of medical therapy without repeated cardiac catheterization; (3) serial monitoring of at-risk patients for pulmonary hypertension to optimize timing of heart transplant referral; (4) and hemodynamic assessment with exercise (5) or after ventricular assist device placement. IHM has the potential to reduce the number of cardiac catheterizations in anatomically complex patients and, in patients with Fontan circulation, IHM pressures may have prognostic implications. In conclusion, though further studies are needed, as patients with CHD age and HF is more prevalent, this tool may assist CHD physicians in caring for this complex patient population.

Comprehensive Approach to the Management of Patients with HLHS: Analysis of 100 Consecutive Neonates.

BACKGROUND: We report our comprehensive approach to patients with hypoplastic left heart syndrome (HLHS) and describe our outcomes in 100 consecutive neonates. METHODS: One-hundred consecutive neonates (2015-2023) were stratified into 3 pathways: Pathway(1): 77/100=77% were standard-risk and underwent initial Norwood (Stage 1). Pathway(2): 10/100=10% were high-risk with noncardiac risk factors and underwent initial Hybrid Stage 1. Pathway(3): 13/100=13% were high-risk with cardiac risk factors: 10 underwent initial Hybrid Stage 1 + ventricular assist device insertion (HYBRID+VAD), while 3 underwent primary transplantation. RESULTS: One-year mortality=9/100=9%. Pathway(1): Operative Mortality for initial Norwood (Stage 1)=2/77=2.6%. Of 75 survivors of Norwood (Stage 1): 72 underwent successful Glenn, 2 underwent successful biventricular repair, and 1 underwent successful cardiac transplantation. Pathway(2): Operative Mortality for initial Hybrid Stage 1 without VAD=1/10=10%. Of 9 survivors of Hybrid (Stage 1): 4 underwent successful cardiac transplantation, 2 died while awaiting cardiac transplantation, 3 underwent Comprehensive Stage 2 (with 1 death), and 1 underwent successful biventricular repair. Pathway(3): Of 10 HYBRID+VAD: 7/10=70% underwent successful cardiac transplantation and are alive today and 3/10=30% died on VAD while awaiting transplantation. Median VAD support time=134 days (range=56-226). (Two of three patients who were bridged-to-transplant with prostaglandin underwent successful transplantation and one died while awaiting transplantation.) CONCLUSIONS: A comprehensive approach to the management of patients with HLHS is associated with Operative Mortality after Norwood of 2/77=2.6% and an overall one-year mortality of 9/100=9%. 10/100 patients=10% were stabilized with HYBRID+VAD while awaiting transplantation. VAD facilitates survival on the waiting list during prolonged wait times.

Nf1 deficiency modulates the stromal environment in the pretumorigenic rat mammary gland.

Background: Neurofibromin, coded by the NF1 tumor suppressor gene, is the main negative regulator of the RAS pathway and is frequently mutated in various cancers. Women with Neurofibromatosis Type I (NF1)-a tumor predisposition syndrome caused by a germline NF1 mutation-have an increased risk of developing aggressive breast cancer with poorer prognosis. The mechanism by which NF1 mutations lead to breast cancer tumorigenesis is not well understood. Therefore, the objective of this work was to identify stromal alterations before tumor formation that result in the increased risk and poorer outcome seen among NF1 patients with breast cancer. Approach: To accurately model the germline monoallelic NF1 mutations in NF1 patients, we utilized an Nf1-deficient rat model with accelerated mammary development before presenting with highly penetrant breast cancer. Results: We identified increased collagen content in Nf1-deficient rat mammary glands before tumor formation that correlated with age of tumor onset. Additionally, gene expression analysis revealed that Nf1-deficient mature adipocytes in the rat mammary gland have increased collagen expression and shifted to a fibroblast and preadipocyte expression profile. This alteration in lineage commitment was also observed with in vitro differentiation, however, flow cytometry analysis did not show a change in mammary adipose-derived mesenchymal stem cell abundance. Conclusion: Collectively, this study uncovered the previously undescribed role of Nf1 in mammary collagen deposition and regulating adipocyte differentiation. In addition to unraveling the mechanism of tumor formation, further investigation of adipocytes and collagen modifications in preneoplastic mammary glands will create a foundation for developing early detection strategies of breast cancer among NF1 patients.

p53 modulates kinase inhibitor resistance and lineage plasticity in NF1-related MPNSTs.

Malignant peripheral nerve sheath tumors (MPNSTs) are chemotherapy resistant sarcomas that are a leading cause of death in neurofibromatosis type 1 (NF1). Although NF1-related MPNSTs derive from neural crest cell origin, they also exhibit intratumoral heterogeneity. TP53 mutations are associated with significantly decreased survival in MPNSTs, however the mechanisms underlying TP53-mediated therapy responses are unclear in the context of NF1-deficiency. We evaluated the role of two commonly altered genes, MET and TP53, in kinome reprograming and cellular differentiation in preclinical MPNST mouse models. We previously showed that MET amplification occurs early in human MPNST progression and that Trp53 loss abrogated MET-addiction resulting in MET inhibitor resistance. Here we demonstrate a novel mechanism of therapy resistance whereby p53 alters MET stability, localization, and downstream signaling leading to kinome reprogramming and lineage plasticity. Trp53 loss also resulted in a shift from RAS/ERK to AKT signaling and enhanced sensitivity to MEK and mTOR inhibition. In response to MET, MEK and mTOR inhibition, we observed broad and heterogeneous activation of key differentiation genes in Trp53-deficient lines suggesting Trp53 loss also impacts lineage plasticity in MPNSTs. These results demonstrate the mechanisms by which p53 loss alters MET dependency and therapy resistance in MPNSTS through kinome reprogramming and phenotypic flexibility.

Ex Vivo Patient-Derived Explant Model for Neurofibromatosis Type 1-Related Cutaneous Neurofibromas.

Cutaneous neurofibromas (CNFs) are benign tumors that occur in the dermis of individuals with the inherited tumor predisposition disorder, neurofibromatosis type 1. CNFs cause disfigurement, pain, burning, and itching, resulting in substantially reduced QOL in patients with neurofibromatosis type 1. CNFs are benign tumors that exhibit cellular and molecular heterogeneity, making it difficult to develop tractable in vitro or in vivo models. As a result, CNF research and drug discovery efforts have been limited. To address this need, we developed a reproducible patient-derived explant (PDE) ex vivo culture model using CNF tumors from patients with neurofibromatosis type 1. CNF PDEs remain viable in culture for over 9 days and recapitulate the cellular composition and molecular signaling of CNFs. Using CNF PDEs as a model system, we found that proliferation was associated with increased T-cell infiltration. Furthermore, we identified a pattern of reciprocal inflammatory signaling in CNF PDEs in which tumors rely on prostaglandin or leukotriene-mediated signaling pathways. As proof of principle, we show that ex vivo glucocorticoid treatment reduced the expression of proinflammatory genes, confirming that CNF PDEs are a useful model for both mechanistic studies and preclinical drug testing.

NF1 deficiency drives metabolic reprogramming in ER+ breast cancer.

OBJECTIVE: NF1 is a tumor suppressor gene and its protein product, neurofibromin, is a negative regulator of the RAS pathway. NF1 is one of the top driver mutations in sporadic breast cancer such that 27 % of breast cancers exhibit damaging NF1 alterations. NF1 loss-of-function is a frequent event in the genomic evolution of estrogen receptor (ER)+ breast cancer metastasis and endocrine resistance. Individuals with Neurofibromatosis type 1 (NF) - a disorder caused by germline NF1 mutations - have an increased risk of dying from breast cancer [1-4]. NF-related breast cancers are associated with decreased overall survival compared to sporadic breast cancer. Despite numerous studies interrogating the role of RAS mutations in tumor metabolism, no study has comprehensively profiled the NF1-deficient breast cancer metabolome to define patterns of energetic and metabolic reprogramming. The goals of this investigation were (1) to define the role of NF1 deficiency in estrogen receptor-positive (ER+) breast cancer metabolic reprogramming and (2) to identify potential targeted pathway and metabolic inhibitor combination therapies for NF1-deficient ER + breast cancer. METHODS: We employed two ER+ NF1-deficient breast cancer models: (1) an NF1-deficient MCF7 breast cancer cell line to model sporadic breast cancer, and (2) three distinct, Nf1-deficient rat models to model NF-related breast cancer [1]. IncuCyte proliferation analysis was used to measure the effect of NF1 deficiency on cell proliferation and drug response. Protein quantity was assessed by Western Blot analysis. We then used RNAseq to investigate the transcriptional effect of NF1 deficiency on global and metabolism-related transcription. We measured cellular energetics using Agilent Seahorse XF-96 Glyco Stress Test and Mito Stress Test assays. We performed stable isotope labeling and measured [U-13C]-glucose and [U-13C]-glutamine metabolite incorporation and measured total metabolite pools using mass spectrometry. Lastly, we used a Bliss synergy model to investigate NF1-driven changes in targeted and metabolic inhibitor synergy. RESULTS: Our results revealed that NF1 deficiency enhanced cell proliferation, altered neurofibromin expression, and increased RAS and PI3K/AKT pathway signaling while constraining oxidative ATP production and restricting energetic flexibility. Neurofibromin deficiency also increased glutamine influx into TCA intermediates and dramatically increased lipid pools, especially triglycerides (TG). Lastly, NF1 deficiency alters the synergy between metabolic inhibitors and traditional targeted inhibitors. This includes increased synergy with inhibitors targeting glycolysis, glutamine metabolism, mitochondrial fatty acid transport, and TG synthesis. CONCLUSIONS: NF1 deficiency drives metabolic reprogramming in ER+ breast cancer. This reprogramming is characterized by oxidative ATP constraints, glutamine TCA influx, and lipid pool expansion, and these metabolic changes introduce novel metabolic-to-targeted inhibitor synergies.

Age moderates change in disease-related stress among congenital heart disease survivors: a 6-year follow-up.

AIMS: As congenital heart disease (CHD) survivors age, they are confronted with elevated risk of cardiovascular morbidity and increasingly complex disease self-management demands. Given that stress is associated with poor physical and psychosocial outcomes, it is crucial to examine how disease-related stress changes over time in this population. However, this outcome has received little research attention to date. This study aimed to identify demographic and clinical predictors of change in disease-related stress over 6 years among CHD survivors. METHODS AND RESULTS: Congenital heart disease survivors (N = 252, Mage = 25.6 ± 7.1, 52.9% female) completed the first 13 items of the Responses to Stress Questionnaire, adapted for use among CHD survivors, to assess disease-related stressors at study entry (T1) and 6-year follow-up (T2). Age, gender, estimated family income, and New York Heart Association (NYHA) functional class at T1 were entered into mixed linear models to determine their impact on change in disease-related stress. Older age (P < 0.001), lower income (P < 0.001), and presence of functional limitations (NYHA ≥ II) (P < 0.001) predicted greater increases in disease-related stress. When controlling for NYHA, functional class, and income, a significant time by age interaction was identified such that disease-related stress increased over time among those who were adolescents at T1 [b = 4.20, P = 0.010, 95% confidence interval (1.01, 7.40)], but remained stable among young adults. CONCLUSION: The transition from adolescence to adulthood may be a period of increasing disease-related stress. Healthcare providers should consider screening adolescents for elevated disease-related stress during transition education and provide resources to bolster resilience.

Novel uses for implanted haemodynamic monitoring in adults with subaortic right ventricles.

BACKGROUND: Pulmonary hypertension (PH) is a common complication in patients with complete dextro-transposition of the great arteries (TGA) after atrial switch (D-TGA/AS) and congenitally corrected TGA (ccTGA). In this population with subaortic right ventricles (sRVs), echocardiography is a poor screening tool for PH; implantable invasive haemodynamic monitoring (IHM) could be used for this purpose, but data are limited. The aim of this study is to report on novel uses of IHM in patients with sRV. METHODS: This retrospective study describes the uses of IHM, impact of IHM on heart failure hospitalisation (HFH) and device-related complications in adults with sRV from a single centre (2015-2022). RESULTS: IHM was placed in 18 patients with sRV (median age 43 (range 30-54) years, 8 female, 16 with D-TGA/AS, 2 with ccTGA); 16 had moderate or severe sRV systolic dysfunction, 13 had PH on catheterisation. IHM was used for (1) Medical therapy titration, (2) Medical management after ventricular assist device in patients with transplant-limiting PH and (3) Serial monitoring of pulmonary artery pressures without repeat catheterisations to help identify the optimal time for heart transplant referral. In follow-up (median 23 months), HFHs/year were similar to the year prior to IHM (median 0 (IQR 0-1.0) before vs 0 (0-0.8) after, p=0.984). Device migration occurred in one, without long-term sequelae. CONCLUSIONS: Uses of IHM in patients with sRV are described which may minimise the need for serial catheterisations in a population where PH is prevalent. HFHs were low overall but not impacted by IHM. One device-related complication occurred without long-term consequence.

Early Experience and Lessons Learned Using Implanted Hemodynamic Monitoring in Patients With Fontan Circulation.

BACKGROUND: Data on the use of implanted hemodynamic monitoring (IHM) in patients with Fontan circulation are limited. This study reports our experience using the CardioMEMS HF system in adults with Fontan circulation. METHODS AND RESULTS: This single-center, retrospective study evaluated heart failure hospitalizations, procedural complications, and device-related complications in patients with Fontan circulation referred for IHM placement (2015-2022). The association of pulmonary artery pressure (by most recent catheterization and median IHM pressure within 30 days of placement) with both death and follow-up Model for End-Stage Liver Disease Excluding International Normalized Ratio score were evaluated. Of 18 patients referred for IHM placement, 17 were successful (median age, 30 [range 21-48] years, 6 women). Procedural complications (access site hematomas, pulmonary artery staining) occurred in 3 patients, without device-related procedural complications. In follow-up (median, 35 [range, 6-83] months), 1 patient developed a pulmonary embolism (possibly device-related). Heart failure hospitalizations/year were similar before and after IHM (median, 1 [interquartile range, 0-1.0] versus 0.6 [0-2.3]; P=0.268), though only 46% of heart failure hospitalizations had associated IHM transmissions. IHM pressures were associated with Model for End-Stage Liver Disease Excluding International Normalized Ratio scores (R2=0.588, P<0.001), though catheterization pressures were not (R2=0.140, P=0.139). The long-term mortality rate was 53% in this cohort. On unadjusted survival analysis, IHM pressures ≥18 mm Hg were associated with mortality (log rank P=0.041), which was not reproduced with catheterization pressures (log rank P=0.764). CONCLUSIONS: In patients with Fontan circulation, IHM did not reduce heart failure hospitalizations, though patient adherence to transmission was low. Device-related complications were low. IHM pressures may better represent real-life conditions compared with catheterization given associations with mortality and Model for End-Stage Liver Disease Excluding International Normalized Ratio score.

Healthcare Use Among Black and White Congenital Heart Disease Medicaid Enrollees.

Congenital heart disease (CHD) is the most common birth anomaly in the US. Research shows lost-to-follow-up trends and racial disparities in healthcare use. This study examines racial differences in healthcare use among Medicaid-covered children with CHD. Using 2010-2019 claims data from a pediatric Medicaid Accountable Care Organization, 960 Black and White children with complex CHD and ≥ 3 years of continuous Medicaid coverage were identified. Three cohorts were constructed (starting age: < 1-year-olds, 1-5-year-olds, 6-15-year-olds) and followed for 3 years. Multivariate analysis assessed annual healthcare use (cardiology, primary care, emergency department) by race, adjusting for patient and provider covariates. Overall, 51% of patients had an annual cardiology visit, and 54% had an annual primary care visit. Among the 1-5-year-old cohort, Black children were predicted to be 13% less likely to have an annual cardiology visit compared to their White counterparts (p = 0.001). Older Black children were predicted to be more likely to have a primary care visit compared to their White counterparts. Nearly half of Medicaid-enrolled children with complex CHD did not receive recommended cardiology care. Young Black children were less likely to receive an annual cardiac visit, while older Black children were more likely to receive primary care. While the percentage with an annual cardiac visit was low, the majority had seen a cardiologist within the 3-year window, suggesting these children are still receiving cardiology care, if less frequently than recommended. Opportunities exist for cardiology and primary care to collaborate to ensure patients receive timely recommended care.

Ultrasonographic measurement of caudal vena cava to aorta ratio during fluid resuscitation of dogs with spontaneous circulatory shock.

OBJECTIVES: To describe the change in the caudal vena cava to aorta ratio (CVC:Ao) ratio during fluid resuscitation of circulatory shock in dogs and compare these results with those of the physical examination and blood lactate. MATERIALS AND METHODS: Perfusion parameters and blood lactate were recorded at admission. An abdominal point-of-care ultrasound protocol was performed, during which the caudal vena cava to aorta ratio was measured on the spleno-renal view. Measurements were performed within 5 minutes before and after a 10 mL/kg crystalloid fluid bolus. Investigators were not blinded to therapeutic interventions. RESULTS: Twenty-nine dogs with physical signs of circulatory shock were enrolled. Caudal vena cava to aorta ratios were below reference interval in 28 of 29 dogs. After bolus administration, median caudal vena cava diameter increased by 0.14 cm (0.69 to 0.83 cm) and median aorta diameter increased by 0.03 cm (0.87 to 0.90 cm) and caudal vena cava to aorta ratio returned to within reference range in 65% of dogs (13/29). Bolus administration was associated with an increase in median caudal vena cava to aorta ratio of 0.10 (95% CI:0.05 to 0.16, P=0.0005). Blood lactate did not change significantly. Heart rate and capillary refill time decreased significantly after fluid bolus (heart rate: estimate=-19 bpm, 95% CI:-30 to -8, P=0.002; capillary refill time: estimate=-1.0 s, 95% CI:-1.3 to -0.7, P < 0.0001). CLINICAL SIGNIFICANCE: In this population of dogs with circulatory shock, the caudal vena cava to aorta ratio significantly increased after a fluid bolus. Future studies that implement blinding of the outcome assessors are warranted to confirm these findings.

Patient Experience with Telemedicine in Adults with Congenital Heart Disease.

Introduction: The COVID-19 pandemic has resulted in increased use of telemedicine. There are limited data on patient experience with telemedicine in adults with congenital heart disease (ACHD). We hypothesized that due to their complex medical history, ACHD would prefer in-person clinic visits over telemedicine. Methods: We conducted a nurse-administered telephone survey based on Agency for Healthcare Research and Quality recommendations to assess patient experience after ACHD telemedicine visits in the early part of the pandemic from March 2020 to June 2020. Results: Of 216 ACHD who had telemedicine visits, 136 (63%) agreed to participate in the survey. Mean age was 45 ± 18 years, majority (65%) being video encounters. Most (98%) patients expressed that the telemedicine visit was successful in addressing their health care needs. Only 21 (15%) patients reported technical issues. Most patients (76%) preferred telemedicine given testing was provided separately, 25 (18%) preferred in-person clinic visits, and 8 (6%) had no preference. Of the 25 patients over 65 years, 19 (76%) would choose telemedicine over the in-person clinic, and only 1 patient reported technical difficulties. Conclusion: ACHD reported a positive experience with telemedicine. Technical limitations were infrequent even among the elderly. The majority of patients felt that their health care needs were addressed and would consider telemedicine over clinic visits. These data are important as payors move away from supporting telemedicine and hospitals restructure, with and without ongoing COVID-19 concerns.

Changing epidemiology of congenital heart disease: effect on outcomes and quality of care in adults.

The epidemiology of congenital heart disease (CHD) has changed in the past 50 years as a result of an increase in the prevalence and survival rate of CHD. In particular, mortality in patients with CHD has changed dramatically since the latter half of the twentieth century as a result of more timely diagnosis and the development of interventions for CHD that have prolonged life. As patients with CHD age, the disease burden shifts away from the heart and towards acquired cardiovascular and systemic complications. The societal costs of CHD are high, not just in terms of health-care utilization but also with regards to quality of life. Lifespan disease trajectories for populations with a high disease burden that is measured over prolonged time periods are becoming increasingly important to define long-term outcomes that can be improved. Quality improvement initiatives, including advanced physician training for adult CHD in the past 10 years, have begun to improve disease outcomes. As we seek to transform lifespan into healthspan, research efforts need to incorporate big data to allow high-value, patient-centred and artificial intelligence-enabled delivery of care. Such efforts will facilitate improved access to health care in remote areas and inform the horizontal integration of services needed to manage CHD for the prolonged duration of survival among adult patients.

Timely PAH Identification in Adults With Repaired Congenital Heart Disease? The ACHD-QuERI Registry Insights.

Background: The Quality Enhancement Research Initiative (QuERI) in adults with congenital heart disease (ACHD) was developed to improve detection of pulmonary arterial hypertension (PAH) after repair of systemic-to-pulmonary arterial shunt lesions. Objectives: This study sought to standardize use of accepted criteria for PAH diagnosis and evaluate utility in at-risk patients with ACHD. Methods: Patients ≥18 years of age with ACHD repaired ≥1 year before enrollment and with additional risk factors for developing PAH were eligible. History, physical examination, electrocardiogram, transthoracic echocardiogram, World Health Organization functional class, and 6-minute walk distance were evaluated at baseline and yearly for 3 years. Pop-up reminders of patient-specific evidence-based recommendations for PAH detection appeared during data entry. Results: Among 217 eligible patients, mean age (enrollment) was 44.0 ± 15.9 years, 72.3% were women, and 82.0% were World Health Organization functional class I. Electrocardiogram was performed in >80% and TTE in >70% of patients annually; capture of required transthoracic echocardiography (TTE) measures and alignment between study- and core-center interpretation improved over time, with more frequent assessment of pulmonary arterial flow acceleration time and documentation of right ventricular outflow tract Doppler notching. Approximately 40% of patients had ≥2 high-risk features for PAH on TTE, but only 7% (6/82) underwent right heart catheterization (RHC). Using current definitions, 2 patients were confirmed by RHC to have a diagnosis of PAH (maximum follow-up 3 years). Conclusions: A structured protocol may improve screening for patients with repaired ACHD at risk of developing PAH. RHC may be underutilized in patients with ACHD with TTE findings suggestive of PAH. (Adult Congenital Heart Disease Registry [QuERI]; NCT01659411).

The effect of corn silage hybrid and inclusion on performance of finishing steers and silage hybrid effects on digestibility and performance of growing steers.

Three experiments evaluated the effects of three corn silage hybrids, inclusion, and nutrient digestibility in growing and finishing diets. The three hybrids tested included a control (CON), a hybrid containing a brown midrib (bm3) trait (BM3), and an experimental bm3 hybrid with the soft endosperm trait (BM3-SOFT). Experiment 1 utilized 360 crossbred steers (body weight [BW] = 334; SD = 25 kg) to evaluate inclusion of silage in a finishing diet at (15% or 45% of diet dry matter [DM]) and silage hybrid (CON, BM3, or BM3-SOFT). Experiment 2 and 3 utilized 216 crossbred steers (BW = 324; SD = 10 kg) and six ruminally fistulated steers (BW = 274; SD = 27 kg), respectively, to evaluate effects of either CON, BM3, or BM3-SOFT silage hybrids on performance and nutrient digestibility in growing diets. In Exp. 1, there was a silage inclusion × hybrid interaction for average daily gain (ADG) and gain-to-feed ratio (G:F). All treatments with 15% silage had greater (P ≤ 0.04) ADG and G:F compared with 45% silage. Cattle fed BM3-SOFT had greater ADG and G:F than cattle fed CON or BM3 when silage was included at 15% of the diet. When silage was fed at 45% of the diet DM, ADG did not differ between cattle fed either bm3 hybrid. Cattle fed BM3 had the greatest G:F (P < 0.01), with no difference between BM3-SOFT and CON. At 15% silage inclusion, hot carcass weight (HCW) was greater (P < 0.01) for cattle fed BM3-SOFT compared with cattle fed CON and BM3 but did not differ between cattle fed BM3 and CON. At 45% silage inclusion, steers fed either bm3 hybrid did not differ in HCW but were both heavier (P < 0.01) compared with cattle fed CON. In Exp. 2, ending BW, dry matter intake (DMI), and ADG were greater (P < 0.01) for steers fed either bm3 hybrid compared to steers fed the CON, but not different between steers fed the bm3 hybrids. There were no differences (P = 0.26) in G:F between the silage hybrids. In Exp. 3, steers fed either bm3 had greater (P < 0.01) neutral detergent fiber (NDF) and acid detergent fiber (ADF) digestibility than steers fed the CON. Ruminal pH was lower (P < 0.01), and total volatile fatty acid (VFA) concentration was greater (P < 0.01) for steers fed bm3 hybrids compared to steers fed CON. Feeding silage with the bm3 trait improved fiber digestibility, which increased DMI and subsequent ADG in high-forage growing diets. Feeding corn silage with the bm3 trait improved performance compared to non-bm3 corn silage when included above typical roughage concentration.