Left atrio‐ventricular valve degeneration, left ventricular dilation and right ventricular failure: A possible association with pulmonary hypertension and aetiology of ascites in broiler chickens

A new application of nano-selenium: rescue of CK2 and mitochondria from oxidative stress to prevent cardiac hypertrophy

Background: Excessive reactive oxygen species (ROS) and subsequent mitochondrial dysfunction are pivotal in initiating cardiac hypertrophy. To explore nano-selenium's (SeNP's) preventive potential against this condition, the authors evaluated chemically synthesized chitosan-SeNPs and biosynthesized Bacillus cereus YC-3-SeNPs in an angiotensin II (Ang II)-induced cardiac hypertrophy model. Methods: This investigation encompassed ROS measurement, mitochondrial membrane potential analysis, transmission electron microscopy, gene and protein expression analyses, protein carbonylation assays, serum antioxidant quantification and histological staining. Results: SeNPs effectively countered Ang II-induced cardiac hypertrophy by reducing ROS, restoring mitochondrial and protein kinase 2α (CK2-α) function, activating antioxidant pathways and enhancing serum antioxidant levels. Conclusion: This finding underscores SeNPs' role in attenuating Ang II-induced myocardial hypertrophy both in vitro and in vivo.

Pathophysiology and pathological remodelling associated with dilated cardiomyopathy in broiler chickens predisposed to heart pump failure

Broiler chickens selected for rapid growth are highly susceptible to dilated cardiomyopathy (DCM). In order to elucidate the pathophysiology of DCM, the present study examines the fundamental features of pathological remodelling associated with DCM in broiler chickens using light microscopy, transmission electron microscopy (TEM), and synchrotron Fourier Transform Infrared (FTIR) micro-spectroscopy. The morphological features and FTIR spectra of the left ventricular myocardium were compared among broiler chickens affected by DCM with clinical signs of heart pump failure, apparently normal fast-growing broiler chickens showing signs of subclinical DCM (high risk of heart failure), slow-growing broiler chickens (low risk of heart failure) and Leghorn chickens (resistant to heart failure, used here as physiological reference). The findings indicate that DCM and heart pump failure in fast-growing broiler chickens are a result of a complex metabolic syndrome involving multiple catabolic pathways. Our data indicate that a good deal of DCM pathophysiology in chickens selected for rapid growth is associated with conformational changes of cardiac proteins, and pathological changes indicative of accumulation of misfolded and aggregated proteins in the affected cardiomyocytes. From TEM image analysis it is evident that the affected cardiomyocytes demonstrate significant difficulty in the disposal of damaged proteins and maintenance of proteostasis, which leads to pathological remodelling of the heart and contractile dysfunction. It appears that the underlying causes of accumulation of damaged proteins are associated with dysregulated auto phagosome and proteasome systems, which, in susceptible individuals, create a milieu conducive for the development of DCM and heart failure. RESEARCH HIGHLIGHTS The light and electron microscopy image analyses revealed degenerative changes and protein aggregates in the cardiomyocytes of chickens affected by DCM. The analyses of FTIR spectra of the myocardium revealed that DCM and heart pump failure in broiler chickens are associated with conformational changes of myocardial proteins. The morphological changes in cardiomyocytes and conformational changes in myocardial proteins architecture are integral constituents of pathophysiology of DCM in fast-growing broiler chickens.

Effect of a background Ca2+ entry pathway mediated by TRPC1 on myocardial damage of broilers with induced ascites syndrome

Ascites syndrome (AS) in chickens is associated with profound vascular remodelling and increased pulmonary artery pressure as well as right ventricular hypertrophy. Classical transient receptor potential cation channels (TRPCs) are key regulators of cardiac hypertrophy that act via regulation of calcium influx in mammals. We investigated whether classical transient receptor potential channels in chickens with right ventricular hypertrophy still possess this mechanism for regulating Ca²⁺ flux. Intravenous injection of cellulose particles was successfully used to induce AS in chickens, and tissues were examined 22 days after treatment. The chickens in the test group showed cardiac hypertrophy with oedema of the cardiac muscle and disruption of myofilaments. The right-to-total ventricle weight ratio (RV/TV), the levels of serum aspartate aminotransferase (AST) and creatine kinase (CK) of the test group were significantly higher than in the control group. Intracellular calcium levels were significantly increased in cardiomyocytes from chickens in the test group. Gene expression of TRPC3, TRPC4, TRPC5, TRPC6 and TRPC7 in heart tissues from the test group showed no significant differences compared with controls. However, TRPC1 protein levels, as well as mRNA levels, were down-regulated in the heart muscle of AS chickens (P < 0.05). Although we observed an increase in calcium concentration, the expression of TRPC1 decreased in cardiac cells. We hypothesized that an increase in intracellular free calcium concentration could inversely regulate calcium channel expression. RESEARCH HIGHLIGHTS Intracellular Ca²⁺ levels were increased in the myocardium of AS broilers. Expression of TRPC1, which mediates calcium influx, was decreased in the myocardium of AS broilers. The relationship between intracellular Ca²⁺ levels and expression of TRPC1 requires further study.

Effects of different floor materials on the welfare and behaviour of slow- and fast-growing broilers

Litter quality and fast growth rate are the two main issues in broiler welfare. This study aimed to evaluate the effects of genotype and floor material on broiler welfare and behaviour. In the study, slow-growing (Hubbard JA57) and fast-growing (Ross 308) broilers on a slatted floor and deep litter were used; there were four main groups (2 genotype  ×  2 housing) and each treatment group consisted of 5 replicates. Each replicate group consisted of 10 male chicks, and 200 birds were used in total. The experiment lasted for 8 weeks. The welfare parameters were recorded in weeks 6, 7, and 8, whereas behaviour data were collected in week 8 only. Results showed that welfare parameters of broiler chickens were affected by genotype and floor type. Slow-growing broilers had better welfare parameters than fast-growing broilers. The slatted floor had a positive effect on main welfare parameters of the birds. Slower-growing broilers had a longer distance in the avoidance distance test. Tonic immobility reaction was longer in slow-growing broilers compared to fast-growing broiler. On the other hand, floor type did not affect behaviour parameters. As a conclusion, slow-growing broilers had better welfare parameters than fast-growing broilers and slat flooring could be beneficial to improve broiler welfare, but further behavioural investigations are needed such as dust bathing and walking behaviour.

Over, and underexpression of endothelin 1 and TGF-beta family ligands and receptors in lung tissue of broilers with pulmonary hypertension

Transforming growth factor beta (TGF β ) is a family of genes that play a key role in mediating tissue remodeling in various forms of acute and chronic lung disease. In order to assess their role on pulmonary hypertension in broilers, we determined mRNA expression of genes of the TGF β family and endothelin 1 in lung samples from 4-week-old chickens raised either under normal or cold temperature conditions. Both in control and cold-treated groups of broilers, endothelin 1 mRNA expression levels in lungs from ascitic chickens were higher than levels from healthy birds (P < 0.05), whereas levels in animals with cardiac failure were intermediate. Conversely, TGF β 2 and TGF β 3 gene expression in lungs were higher in healthy animals than in ascitic animals in both groups (P < 0.05). TGF β 1, T β RI, and T β RII mRNA gene expression among healthy, ascitic, and chickens with cardiac failure showed no differences (P > 0.05). BAMBI mRNA gene expression was lowest in birds with ascites only in the control group as compared with the values from healthy birds (P < 0.05).

Pulmonary vascular pressure profiles in broilers selected for susceptibility to pulmonary hypertension syndrome: age and sex comparisons

Broilers that are susceptible to pulmonary hypertension syndrome (PHS, ascites) have an elevated pulmonary arterial pressure (PAP) when compared with PHS-resistant broilers. Two distinctly different syndromes, pulmonary arterial hypertension and pulmonary venous hypertension (PVH), both are associated with increases in PAP. Pulmonary arterial hypertension occurs when the right ventricle must elevate the PAP to overcome increased resistance to flow through restrictive pulmonary arterioles upstream from the pulmonary capillaries. In contrast, PVH is commonly caused by increased downstream (postcapillary) resistance. The sites of resistance to pulmonary blood flow are deduced by making contemporaneous measurements of the PAP and the wedge pressure (WP) and calculating the transpulmonary pressure gradient (TPG) (TPG = PAP - WP). We obtained PAP and WP values from 8-, 12-, 16-, 20-, and 24-wk-old anesthetized male and female broilers from a PHS-susceptible line. Pressures were recorded as a catheter was advanced through a wing vein to the pulmonary artery and onward until the WP was obtained. In addition to sex and age comparisons of vascular pressure gradients, the data also were pooled to obtain 3 cohorts for broilers having the lowest PAP values (n = 52; range: 12 to 22.9 mmHg), intermediate PAP values (n = 63; range: 23 to 32.9 mmHg), and highest PAP values (n = 62; range: 33 to 62 mmHg) independent of age or sex. Within each of the age, sex, and PAP cohort comparisons, broilers with elevated PAP consistently exhibited the hemodynamic characteristics of pulmonary arterial hypertension (elevated PAP and TPG combined with a normal WP) and not PVH (elevated PAP and WP combined with a normal or reduced TPG). Susceptibility to PHS can be attributed primarily to pulmonary arterial hypertension associated with increased precapillary (arteriole) resistance.

Chronic heart failure due to severe endocardiosis in a Gambian giant pouched rat (Cricetomys gambianus)

A 1.5-yr-old captive male Gambian giant pouched rat (Cricetomys gambianus) died after suffering from anorexia, weakness, and dyspnea for 3 wk. Thoracic radiographs of thorax and abdomen and computed tomography showed a severe biventricular enlargement of the heart and a moderate hepatomegaly. Necropsy revealed a severe, bilateral hypertrophic cardiomyopathy and dilation of the right ventricle due to multifocal bilateral, valvular endocardiosis of all atrioventricular valves and acute hepatic congestion. Histologically, the atrioventricular valves were multifocally thickened by a marked endocardiosis with stromal accumulation of Periodic acid-Schiff (PAS)-positive, mucinous material. Although common in dogs, endocardiosis has not been described in Nesomyidaes. As in other affected species, the pathogenesis of endocardiosis in this species remains unclear.

Ascites in poultry: Recent investigations

In recent years, ascites research has centred on gaining an increased understanding of pulmonary hypertension syndrome together with the potential role of primary cardiac pathologies. The impact at a cellular level of factors which trigger ascites and substances that protect against it has also been documented. Primary pulmonary hypertension has been induced when birds are exposed to hypoxia during incubation. The conditions experienced during this phase of development may impact on the ability of the bird to regulate its basal metabolic rate through endocrine signals controlled by thyroid activity. The extent of ventilation in the lung influences the ability of the bird to oxygenate haemoglobin. Ventilation/ perfusion mismatches may occur prior to or post-hatching. This factor has been studied extensively using the pulmonary artery/bronchus clamp model. At high altitude, a decreased ventilation/perfusion ratio may occur following the effective increase in physiological dead space due to the lowered oxygen tension at the level of the parabronchi. This explains the mechanism by which ascites is triggered by hypoxia in this particular situation. The effects of ascites are ameliorated by the use of beta agonists and dietary arginine, which act by increasing ventilation and blood flow in the lungs and thus correcting a ventilation/perfusion mismatch. Transient bacterial and viral infections may also influence the induction of pulmonary hypertension. The increases in blood viscosity associated with ascites are most probably a consequence of the condition rather than a cause. A bird may alleviate the effects of pulmonary hypertension by decreasing blood viscosity through inhibition of platelet function, increased erythrocyte deformability and the production of coronary relaxants. Evidence is accumulating that primary cardiac pathology may be associated with a number of ascites cases. Broilers that subsequently develop ascites, exhibit lower heart rates than their normal flock mates. Furthermore, during ascites, hypoxic broilers exhibit bradycardia as opposed to the expected tachycardia. In these cases, a tachycardia induced by feed restriction may protect the bird by raising its cardiac output. Right atrio-ventricular regurgitant flow velocities in chickens are relatively slow compared with similar regurgitant flows induced by pulmonary hypertension in other species. The conduction system in the avian heart is specialized and contains a recurrent bundle branch that innervates the right atrio-ventricular valve, thus initiating active valve closure before right ventricular systole. This predisposes the heart to right ventricular volume overload through a valvular incompetance following a failure of valvular innervation. The resultant elevated diastolic wall stress can trigger the production of angiotensin II and its converting enzyme, which mediate ventricular hypertrophy. Subclinical myocardial damage, irrespective of its cause, can be detected by the presence of troponin T in the blood. Reactive oxygen species may damage cell membranes compromising cellular function in a number of body systems. A positive correlation exists between oxidized glutathione concentrations and right ventricular weight ratio. This indicates a failure to cope with oxidative stress at the level of the respiratory membrane. It is not known if it is possible to modulate levels of antioxidants at this location and hence protect the bird. The final description of the ascites aetiology may lie in the concept of a circuit of events between the cardiac, pulmonary and vascular systems that satisfy the metabolic requirements of the bird. A deficit in one of these systems, at a level that prevents adequate compensation from other components, triggers the pathological cascade that results in the end point of clinical ascites.

Biochemical factors limiting myocardial energy in a chicken genotype selected for rapid growth

Broiler chickens (Gallus gallus) genetically selected for rapid growth are inherently predisposed to heart failure. In order to understand the biochemical mechanisms associated with the deterioration of heart function and development of congestive heart failure (CHF) in fast-growing chickens, this study examined several factors critical for myocardial energy metabolism. Measured variables included cardiac energy substrates [creatine phosphate (CrP), adenosine triphosphate (ATP), l-carnitine], activity of selected cytosolic enzymes [creatine kinase (CK; EC 2.7.3.2), lactate dehydrogenase (LDH; EC 1.1.1.27)] and mitochondrial enzymes [pyruvate dehydrogenase (PDH; EC 1.2.4.1), alpha-ketoglutarate dehydrogenase (alpha-KGDH; EC 1.2.4.2)]. The CK activities were higher in fast-growing and CHF broilers as compared to slow-growing broilers (p<0.05). Cardiac LDH and alpha-KGDH activities were not changed (p>0.05), whereas PDH activity was highest (p<0.05) in broilers with CHF. Deterioration of heart function is correlated with lowered cardiac ATP, CrP, and l-carnitine levels (all p<0.05). Depletion of high energy phosphate substrates, ATP and CrP, is evident in fast-growing chickens and those that developed CHF. Increased activity of CK suggests that cardiac energy management in fast-growing broilers and those with CHF largely depends on contribution of this pathway to regeneration of ATP from CrP. In this scenario, inadequate level of CrP is a direct cause of ATP insufficiency, whereas low cardiac l-carnitine, because of its role in fatty acid transport, is most likely an important factor contributing to shortage of key substrate required for synthesis of cardiac ATP. The insufficiencies in cardiac energy substrate synthesis provide metabolic basis of myocardial dysfunction in chickens predisposed to heart failure.

Comparative study of myocardial high energy phosphate substrate content in slow and fast growing chicken and in chickens with heart failure and ascites

In order to explain the biochemical mechanisms associated with deteriorating heart function in broiler chickens, this study compared myocardial high energy phosphate substrates in leghorns, feed restricted (Broilers-Res) broilers, ad libitum fed broilers (Broilers-AL), and in broilers that developed heart failure and ascites. The profile of adenine nucleotide content in the heart tissue did not differ between leghorns and Broilers-Res, but there were significant differences among Broilers-Res, Broilers-AL, and broilers with ascites. During intensive growth periods, leghorns and Broilers-Res showed increasing trends in heart ATP levels, whereas in fast growing broilers the heart ATP declined (p<0.021). ATP:ADP and ATP:CrP ratios increased with age in both leghorn and Broilers-Res, declined in fast growing broilers, and were the lowest in broilers that developed heart failure. The changes in heart high energy phosphate profile in broilers suggest that the energy demand of the heart during a rapid growth phase may exceed the bird's metabolic capacity to supply adequate levels of high energy phosphate substrate. The insufficiency of energy substrate likely contributes to the declining heart rate. In some individuals this may lead to impaired heart pump function, and in more severe cases may progress to heart pump failure.

Pathophysiology of heart failure in broiler chickens: structural, biochemical, and molecular characteristics

Modern strains of fast-growing meat type poultry are highly susceptible to heart failure. Heart-related mortalities are observed predominantly in fast-growing broiler chickens, with ascites and sudden death syndrome being the most common heart-related conditions in modern broiler flocks. This paper examines the role of structural, molecular, and biochemical factors pertinent to the pathophysiology of heart failure in fast-growing broilers. Evidence explaining the pathogenesis of acute and chronic heart failure, in the context of the underlying molecular and biochemical changes in the cardiomyocytes, contractile apparatus, and extracellular matrix in the ventricular myocardium are critically evaluated and discussed with reference to the clinical signs associated with deterioration of heart pump function. The secondary pathophysiological effects on the cardiovascular system, resulting from hemodynamic changes associated with the failing heart pump, are also reviewed and critically discussed.

Rupture of the right auricle in broiler chickens

This report describes a case of cardiac right auricle rupture (RAR) in a flock of 11,500 broilers that were 14 days old. The birds were housed at an altitude of 300 m, with an external temperature of -10 degrees C and an internal temperature of 15 degrees C. There was 3.6% mortality, due to sudden deaths, from 10 to 14 days of age. All necropsied birds had haemopericardium due to RAR at the point of the junction with the vena cava, and 85% of them had blood in the oral cavity and external acoustic meatus. The vena cava and its caudal branches, the intestinal vessels, and the sinus durae matris and sinus saggitalis were distended. Histological examination showed haemorrhages into the myocardium, degeneration of the cardiac muscle fibres, as well as oedema of the lungs and hypertrophy of the smooth muscle bundles of the parabronchial walls. Blood in the mouth of the broilers may have been due to haemoptysis, which in humans is caused mainly by mitral stenosis. In broilers, mitral stenosis and/or insufficiency, and left ventricular failure with consequent pulmonary hypertension (PH) were considered as possible triggers for right ventricular failure. The alarm reaction in hypoxaemia, due to secondary factors such as cold, caused tachycardia and tachypnoea, may have induced further elevation of PH, and acute myocardial infarction causing cardiac rupture and haemopericardium in this case. Hypertension and PH, due to possible mitral stenosis/insufficiency in association with acute myocardial ischaemia, were probably the determinant factors causing this acute episode. This opens the possibility that the RAR may be cardiogenic.

Pathogenesis of Ascites in Broilers Raised at Low Altitude: Aetiological Considerations Based on Echocardiographic Findings

This study reports novel insight into the aetiology of pulmonary hypertension and ascites in broiler chickens. The scope of measurements was focused on anatomical and functional parameters, and blood flow patterns in leghorns (resistant to ascites), fast-growing broilers (susceptible to ascites), broilers developing ascites, and ascitic broilers evaluated in vivo using echocardiography, and further examined in the context of postmortem findings. Both, in vivo observed features and postmortem findings, showed clear differences between broilers and leghorns, and between normal and ascitic broilers. Abnormalities in the heart chamber geometry and blood flow patterns were detected upon echocardiographic examination in all ascitic broilers. Right and left atrio-ventricular (AV) valve regurgitation were common findings in ascitic broilers and some apparently normal broilers, with left AV valve insufficiency being a predominant feature with respect to degree and frequency of occurrence. Blood flow disturbances were not detected in leghorns. Left ventricular fractional shortening (functional parameter) was considerably reduced (P < 0.01) in ascitic birds (mean: 21.7 +/- 2.0 SE) in comparison with normal broilers (mean: 39.1 +/- 3.6 SE), or leghorns (mean: 43.3 +/- 2.4 SE). The presented findings indicate that pathological and functional changes in the left ventricle and atrium play a significant role in the pathogenesis of ascites in broilers. Severe dilation of the left atrium and pulmonary veins seen on postmortem examination, as well as regurgitant blood flow in the left atrium, demonstrated by Doppler study in ascitic birds, provide evidence that chronically elevated pressure in the left atrium is involved in the aetiology of pulmonary hypertension and ascites in fast-growing broilers.

The aetiology of hypoxaemia in chickens selected for rapid growth

In comparison to other classes of chickens, broilers selected for rapid growth tend to be hypoxaemic, and many develop congestive heart failure (CHF). In order to explain the physiological mechanisms associated with hypoxaemia in fast-growing broiler chickens (Gallus gallus), this study examined several basic physiological parameters including the blood gas profile in arterial [left atrial (LA)] and mixed venous [right atrial (RA)] blood, systemic oxygen extraction ratio, and intrapulmonary shunt fraction. These parameters were further studied in the context of blood flow in the pulmonary circulation, structural characteristics of the lungs, and cardiac function [measured as cardiac index (CI)]. Overall, broilers had lower arterial and mixed venous blood pO(2) levels and higher pCO(2) levels compared to leghorns. The cardiac index was lower in fast-growing and CHF broilers compared to leghorn chickens or feed-restricted broilers. Systemic oxygen extraction ratio (ER) and intrapulmonary shunt fraction were significantly higher in fast-growing broilers and birds with CHF (all P<0.01). Lungs of all broilers, but not leghorns, contained ectopic, irregular nodular formations located within air spaces. Broilers with clinical signs of hypoxaemia revealed the highest number of these formations in their lung. Taken together, the present findings indicate that key factors associated with the development of hypoxaemia in fast-growing broilers include: (1) high demand for oxygen as evidenced by high oxygen ER; (2) inadequate cardiac output (CO) to fulfill the higher oxygen demands, leading to severe depletion of O(2) in mixed venous blood; and (3) elevated intrapulmonary shunt fraction and possibly dead space associated with specific pathological and anatomical characteristics within the lung.

Production and growth related disorders and other metabolic diseases of poultry – A review

In humans, metabolic complaints may be associated with a failure in one of the body hormone or enzyme systems, a storage disease related to lack of metabolism of secretory products because of the lack of production of a specific enzyme, or the breakdown or reduced activity of some metabolic function. Some of these disorders also occur in poultry, as do other important conditions such as those associated with increased metabolism, rapid growth or high egg production that result in the failure of a body system because of the increased work-load on an organ or system. These make up the largest group of poultry diseases classified as metabolic disorders and cause more economic loss than infectious agents. Poultry metabolic diseases occur primarily in two body systems: (1) cardiovascular ailments, which in broiler chickens and turkeys are responsible for a major portion of the flock mortality; (2) musculoskeletal disorders, which account for less mortality, but in broilers and turkeys slow down growth (thereby reducing profit), and cause lameness, which remains a major welfare concern. In addition, conditions such as osteoporosis and hypocalcaemia in table-egg chickens reduce egg production and can kill.

Pulmonary wedge pressures confirm pulmonary hypertension in broilers is initiated by an excessive pulmonary arterial (precapillary) resistance

High retrograde pressure through the pulmonary venous system caused by failure of the left ventricle or left atrio-ventricular valve may result in the elevated pulmonary arterial pressure and right ventricular hypertrophy associated with pulmonary hypertension syndrome (PHS; ascites) in broiler chickens. In the present study, unanaesthetized male broilers from an ascites-resistant line, the base population from which the resistant line was derived, and a separate unselected line were used to determine whether changes in wedge pressure (thought to be similar to left atrial pressure) are predictive of differences in the pulmonary arterial pressure of clinically healthy and pre-ascitic broilers. Venous, right atrial, right ventricular, pulmonary arterial, and wedge pressures were obtained by inserting a catheter into a wing vein and progressively advancing the catheter into a pulmonary branch artery until the catheter tip became wedged in and occluded the flow through a terminal artery. Mean right ventricular and pulmonary arterial pressures were lower in the resistant line than in the base population, but wedge pressures did not differ between the resistant, base, and unselected lines. Right:total ventricular weight ratios (RV:TV) and the percentage saturation of hemoglobin with oxygen in arterial blood ranged in value from 0.18 to 0.44 and 65 to 96%, respectively. Wedge pressure, however, remained similar when pre-ascitic broilers with high RV:TV values and low oximetry values were compared with clinically healthy broilers. In all birds, whether healthy or showing pre-ascitic characteristics, the wedge pressure was slightly higher than the right atrial pressure but substantially lower than pulmonary arterial pressure. These observations provide definitive proof that pulmonary hypertension is initiated as a consequence of excessive pulmonary arterial or arteriole resistance. Pulmonary venous pressure is estimated by measuring the pulmonary arterial wedge pressure, and high wedge pressures would be evident if pulmonary hypertension was caused by the elevated downstream resistances associated with left-sided heart failure.

Ultrastructural and molecular changes in the left and right ventricular myocardium associated with ascites syndrome in broiler chickens raised at low altitude

The present study examines ultrastructural and molecular changes in ventricular myocardium associated with ascites cases in fast-growing broilers raised at low altitude. Extensive ultrastructural lesions were seen in the left and right ventricular myocardium of broilers with fulminant heart failure and ascites. Significant changes included lesions in the myofibril contractile apparatus, altered mitochondria, marked reduction in the myofibril component, and changes in the extracellular matrix (ECM) architecture. No lesions were observed in hearts of slow growing broilers, but mild to moderate changes (predominantly in the left ventriculum) were apparent in the hearts from some clinically normal, fast-growing broilers. SDS-PAGE profiles of washed myofibrils showed several distinctly different bands in preparations from left ventricular myocardium of ascitic birds. Western blot analysis of these samples revealed several fragments of myosin heavy chain, M-protein, and titin. Based on gelatinolytic activity, matrix metalloproteinases (MMP) in the cytosolic fraction of ventricular myocardium homogenates were identified as MMP-2. The relative activity of this enzyme appears to be considerably higher in preparations from broilers, particularly in the preparations from the left ventriculum of fast-growing broilers, in comparison to leghorns or slow growing broilers. The nature and distribution of the changes in the heart indicate that chronic cardiomyopathic process in the left ventricular myocardium occurs during the development of ascites. It is postulated that progressive deterioration of the left heart pump function caused by initial lesions in the left ventricular myocardium is a significant factor in the development of pulmonary hypertension and the pathogenesis of ascites in broilers raised at low altitude.

Cardiac output in four-, five-, and six-week-old broilers, and hemodynamic responses to intravenous injections of epinephrine

Female broilers were evaluated at 4, 5, and 6 wk of age (1.2, 1.8, and 2.3 kg BW, respectively) to assess changes in cardiac output and related hemodynamics associated with BW gain, and to evaluate cardiopulmonary hemodynamic adjustments occurring secondary to i.v. injections of epinephrine (0.1 mg/ kg BW). Cardiac output increased with BW (253, 348, and 434 mL/min at 4, 5, and 6 wk, respectively) due to increases in stroke volume (0.70, 1.03, and 1.33 mL/beat) that more than compensated for reductions in heart rate (362, 337, and 328 bpm). Normalization for BW eliminated the differences in cardiac output and stroke volume. Increases in cardiac output were not associated with age- or BW-related increases in mean systemic arterial pressure (101.5, 108.6, and 108.0 mm Hg) due to corresponding reductions in total peripheral resistance (0.41, 0.32, and 0.26 relative resistance units). Epinephrine initially triggered immediate (within 90 s) threefold increases in total peripheral resistance and pulmonary vascular resistance, which, in turn, increased the systemic arterial pressure and pulmonary arterial pressure in spite of concurrent reductions in cardiac output that were associated with diminished venous return and dependent reductions in stroke volume and heart rate. Within 150 s after epinephrine injection, the systemic and pulmonary vascular resistances returned to preinjection control levels. By 300 s postinjection, stroke volume and heart rate increased, causing cardiac output to rise above preinjection control levels, which, in turn, elicited variable pulmonary arterial pressure responses apparently reflecting individual variability in the capacity for flow-dependent pulmonary vasodilation. These studies demonstrate that chronic (age- and BW-related) and acute (epinephrine-induced) changes in cardiac output in broilers reflect complex interactions among hemodynamic variables that include stroke volume, heart rate, and systemic and pulmonary vascular resistances.