Spontaneous hypoxaemia and right ventricular hypertrophy in fast growing broiler chickens reared at sea level

Cardio-pulmonary function in broilers reared at warm or cool temperatures: effect of acute inhalation of 100% oxygen

Fast growth and cool temperatures are the primary triggers for pulmonary hypertension syndrome (PHS, ascites) during commercial broiler growout. We evaluated cardio-pulmonary function in male broilers that initially were reared together at normal brooding temperatures and then were randomly assigned to chambers maintained at 28 C (warm group) or 16 C (cool group). Cardio-pulmonary evaluations were conducted between 35 and 42 d of age. The groups initially did not differ in body weight, right:total ventricular weight ratio, respiratory rate, heart rate, total peripheral resistance, or pulmonary vascular resistance, nor did their arterial blood gas values differ for the partial pressure of carbon dioxide, bicarbonate concentration, or hydrogen ion concentration. When compared with the warm group, the cool group had heavier total ventricular weights and higher values for pulmonary arterial pressure, cardiac output, stroke volume, mean systemic arterial pressure, and hematocrit and a marginally lower (P = 0.06) partial pressure of oxygen. Inhaling 100% O2 for 20 min caused equivalent increases in the arterial partial pressure of oxygen (> or =388 mm Hg) and the percentage saturation of hemoglobin with oxygen (99.9%) in both groups. The respiratory rate was reduced and total peripheral resistance in both groups was increased; the pulmonary arterial pressure, cardiac output, and heart rate in the cool group were also reduced. Cool temperatures contributed to the increase in pulmonary arterial pressure primarily by increasing the metabolic demand for oxygen, as reflected by incipient hypoxemia (reduced blood oxygen and elevated hematocrit), generalized ventricular hypertrophy, and an elevated cardiac output. It was the elevated cardiac output rather than hypoxemic pulmonary vasoconstriction that increased the pulmonary arterial pressure in the cool group when compared with the warm group.

Evaluation of broiler growth velocity and acceleration in relation to pulmonary hypertension syndrome

An evaluation was made of the relationship between individual daily growth patterns and susceptibility of broiler chickens to pulmonary hypertension syndrome (PHS). In the first experiment, 46 male broilers were weighed for each of 50 d, during which time 13 developed PHS. Three temporal phases (0 to 15, 16 to 35, and 36 to 50 d) of broiler growth velocity and acceleration were examined. Correlation dimensions and Lyapunov exponents suggested evidence of chaos in growth velocity and acceleration, but the absence of detectable differences between broilers in the normal and PHS categories led us to reject the hypotheses that growth is more chaotic in normal broilers than in broilers susceptible to PHS. Growth velocity and acceleration values for mean and SD were statistically evaluated as response variables for each growth phase. Mean values for velocity during the third phase were different between broilers in the normal and PHS categories (velocity: 68.8 vs 48.9 g/d, P = 0.03, respectively) and (acceleration: 0.3 vs -1.4 g/d2, P = 0.07, respectively). The third phase SD (reflecting oscillation for velocity and acceleration) was greater for normal than for PHS birds (velocity: 26.1 vs 21.3 g/d, P = 0.13, respectively; acceleration: 39.7 vs 28.2 g/d2, P = 0.03, respectively). The hypothesis was accepted that normal birds have greater oscillations in growth velocity and acceleration than birds susceptible to PHS. A general regression neural network (GRNN) with genetic adaptive calibration was trained to predict PHS based on individual growth phases and their combinations. Data representing the first, first two, and all three phases of growth were determined to have potential for computerized diagnostic weighing. With the GRNN, birds in all three data sets were successfully classified (100%) with or without PHS. A third hypothesis, therefore, was accepted that artificial neural networks could be used to distinguish the difference between normal broilers and those susceptible to PHS. In the second experiment, only one bird was diagnosed with PHS. Velocity and acceleration neural networks from Phase 1 and Phases 1 and 2 in the first experiment were applied to the growth velocity and acceleration data of Experiment 2. The Phase 1 neural networks were the most promising in that they correctly identified 71.6 and 72.4% of the birds as normal for velocity and acceleration data, respectively. In general, data in the second experiment exceeded the neural network range of training for both velocity and acceleration, which reflected increased oscillation during the second phase of growth.

Renal responses of normal and preascitic broilers to systemic hypotension induced by unilateral pulmonary artery occlusion

During the pathophysiological progression of pulmonary hypertension syndrome (PHS; ascites), broilers concurrently develop systemic hypotension (low mean systemic arterial pressure) that may initiate renal retention of water and solute, contributing to fluid accumulation in the abdominal cavity (ascites). In male Single Comb White Leghorns, glomerular filtration is autoregulated over a systemic arterial pressure range of 110 to 60 mm Hg, and corresponding reductions in urine flow are attributed to a phenomenon known as pressure natriuresis. Acute unilateral pulmonary artery occlusion was used in the present study to reduce systemic arterial pressure toward the lower autoregulatory limit for glomerular filtration, and to evaluate kidney function in normal and preascitic broilers. Preascitic broilers characteristically exhibited lower (P < or = 0.05) values for mean systemic arterial pressure (91 vs 100 mm Hg) and percentage saturation of hemoglobin with oxygen (73 vs 84%), higher hematocrits (35 vs 30%), heavier right ventricles (3.44 vs 2.32 g), and higher right:total ventricular weight ratios (0.32 vs 0.24) than normal broilers. Body weights (2,445 vs 2,429 g, respectively), left ventricle plus septum weights (7.16 vs 7.19 g), and heart rates (349 vs 341 beats/min) were similar. Preascitic broilers exhibited larger (P < or = 0.05) dependent reductions in glomerular filtration, urine flow, osmolal clearance, and solute excretion and had a higher free water clearance than normal broilers in response to pulmonary artery occlusion. The differences observed between normal and preascitic broilers demonstrate that systemic hypotension can trigger renal mechanisms contributing to fluid and solute retention during development of PHS.

Venous blood pressure in broilers during acute inhalation of five percent carbon dioxide or unilateral pulmonary artery occlusion

We evaluated the hypothesis that venous congestion (increased venous volume), as reflected by venous hypertension (increased venous pressure), can arise when the right ventricle is unable to elevate the pulmonary arterial pressure sufficiently to propel the cardiac output through an anatomically inadequate or inappropriately constricted pulmonary vasculature. Changes in venous pressure were evaluated in clinically healthy broilers during modest increases in pulmonary vascular resistance induced by inhalation of 5% CO2 and during large increases in pulmonary vascular resistance accomplished by acutely tightening a snare around one pulmonary artery. Inhalation of 5% CO2 induced a pronounced respiratory acidosis, as reflected by increases the partial pressure of CO2 and the hydrogen ion concentration in arterial blood. Inhalation of 5% CO2 also increased pulmonary arterial pressure by approximately 3 mm Hg and increased venous pressure by approximately 1 mm Hg when compared with the pre-inhalation venous pressure. Tightening the pulmonary artery snare increased the pulmonary arterial pressure by approximately 10 mm Hg, and this degree of pulmonary hypertension was sustained until the snare was released. When compared with the pre- and post-snare intervals, tightening of the pulmonary artery snare induced a sustained increase in venous pressure of > or = 1 mm Hg. Veins have highly compliant walls that permit an approximate doubling in volume with only small (4 to 6 mm Hg) increases in central venous pressure. Presumably the apparently modest 1 mm Hg increase in venous pressure measured after CO2 inhalation or unilateral pulmonary artery occlusion reflects a large increase in venous volume and, thus, substantial venous congestion. These observations support the hypothesis that increases in pulmonary vascular resistance can initiate increases in venous pressure by challenging the capacity of the right ventricle to propel all of the returning venous blood through the lungs. Central venous congestion predisposes broilers to the onset of cirrhosis and ascites by impeding the outflow of hepatic venous blood and increasing the hydrostatic pressure within hepatic sinusoids.

High carbon dioxide tension (PCO2) and the incidence of cardiac arrhythmias in rapidly growing broiler chickens

The purpose of this investigation was to determine whether two-week-old rapidly growing broiler chickens with high metabolic activity have an increased risk of the development of heart failure three to five weeks later. The incidence of cardiac arrhythmias was assessed in broiler chickens with either a relatively high carbon dioxide tension (PCO2) or a low PCO2 in their venous blood. Their electrocardiograms (ECGS) were measured when the birds were between five and seven weeks old by means of a biotransplant which allowed them to move freely. Premature ventricular beats were observed in all the birds, but the largest numbers were observed in birds that had had a high PCO2 when they were two weeks old.

Pulmonary artery endothelium-dependent vasodilation is impaired in a chicken model of pulmonary hypertension

Among chicken strains, broilers are prone to pulmonary hypertension, whereas Leghorns are not. Relaxations to endothelium-dependent (ACh, A23187) and endothelium-independent [sodium nitroprusside (SNP), papaverine (PPV)] vasodilators were compared in preconstricted pulmonary artery (PA) rings from these chicken strains. ACh (10(-7), 10(-6), and 10(-5) M)- and A23187 (10(-6) and 10(-5.5) M)-induced relaxations were smaller (P < 0.05) in broilers than Leghorns. N(G)-nitro-L-arginine methyl ester (10(-3.5) M) caused similar reductions in ACh-induced relaxations in both strains. L-Arginine (10(-4) M) enhanced ACh-induced relaxations more in broilers than Leghorns. Relaxations to 10(-10)-10(-6) M SNP did not differ between strains, but were greater (P < 0.05) in broilers than Leghorns at higher concentrations (10(-5) and 10(-4) M). PPV (10(-4) M)- and SNP (10(-4) M)-induced maximal relaxations were greater in broilers than in Leghorns (176.2 +/- 14.7 vs. 120.9 +/- 14.7% and 201.3 +/- 7.8 vs. 171.2 +/- 10.7%, respectively, P < 0.05). Broiler PA rings appear to have increased intrinsic tone and reduced endothelium-derived nitric oxide activity, both of which may contribute to the susceptibility of broiler chickens to pulmonary hypertension.

Performance and physiological variables in broiler chicken lines differing in susceptibility to the ascites syndrome: 1. Changes in blood gases as a function of ambient temperature

1. Male broilers of 5 genetic stocks (A, B, C, D, E) selected in different ways for fast growth and low food conversion ratio (FCR) and differing in ascites sensitivity were subjected to 2 different ambient temperature step down regimens: high temperature (HT: 33 to 20 degrees C over 33 d) and low temperature (LT: 30 to 15 degrees C over 17 d). 2. Ascites incidence was recorded daily. Food intake and body weight gain were measured weekly and FCR was calculated. Heat production (Hp) was calculated using the comparative slaughter method. At 28 d venous samples were taken for blood gas analysis and haematocrit and relative heart, lung and liver weights were recorded. 3. Populations A and C showed the highest growth rates combined with a low FCR and a higher ascites incidence. A low FCR in these stocks was attributable to low values for Hp. These stocks also had low PO2 and high pCO2 in venous blood at low ambient temperature compared with other stocks. Stock B, which exhibited the slowest growth rate and the highest FCR, was not susceptible to ascites and showed higher Hp and PO2 and pCO2 at low ambient temperature. Populations D and E were intermediate for almost all variables. Heart and lung weights were both increased at LT, while liver weight did not differ between temperature regimes. 4. Our results show that a high haematocrit is not necessarily linked with an increased susceptibility to ascites.

Performance and physiological variables in broiler chicken lines differing in susceptibility to the ascites syndrome: 2. Effect of ambient temperature on partial efficiencies of protein and fat retention and plasma hormone concentrations

1. Male broilers of 5 genetic stocks (A, B, C, D and E), selected in different ways for fast growth and low food conversion rate (FCR) and differing in sensitivity to ascites, were subjected to 2 different ambient temperature (Ta) step-down programmes: normal (HT) and low (LT) Ta. 2. Ascites incidence was followed daily. Growth and food intake were measured weekly. Heat production (Hp), oxygen consumption (Oxc) and energy- metabolism parameters were calculated according to the comparative slaughter method. At week 4 blood samples were taken for the analysis of plasma T4, T3, growth hormone (GH) and insulin-like growth factor-I (IGF-1) concentrations. 3. Within-line changes of GH and IGF-1 point to the relative independence of both hormone concentrations. 4. Partial protein efficiency was higher in lines with lower GH, especially at LT. 5. The increase in plasma T3 concentration at LT was accompanied by a decrease in relative fat deposition from the increased energy expenditure. 6. The combination of fast growth and low FCR, linked to a low plasma T4 concentration at LT is indicative of a thyroid insufficiency which is related to an increased occurrence of ascites in these lines.

Broiler breeder survivors of chronic unilateral pulmonary artery occlusion produce progeny resistant to pulmonary hypertension syndrome (ascites) induced by cool temperatures

Chronic occlusion of one pulmonary artery triggers a high incidence of pulmonary hypertension syndrome (PHS, ascites) in broilers. In the present study, the left pulmonary artery was chronically occluded in 295 male and 255 female chicks pedigreed from 18 sire families, leading to PHS in 74% of the males and 45% of the females. Survivors were reared to breeding age and served as parents for the resulting PHS-resistant chicks (Resistant), whereas control chicks were produced from the base population for this line (Base). In two experiments, male and female Resistant and Base chicks were reared separately by sex but mixed by group within environmental chambers, where they were exposed to cool (14 C) temperatures. In both experiments, the incidence of PHS was at least 50% lower in the Resistant males and females than in the Base males and females, respectively. When compared within a sex, the Base and Resistant broilers surviving to the end of both experiments did not differ in final body weight or body weight gain, nor did their right:total ventricular weight (RV:TV) ratios differ. These results demonstrate that broiler breeders capable of thriving after having their entire cardiac output forced to flow through one lung, subsequently produced male and female progeny with substantially improved resistance to the onset of PHS induced by fast growth and exposure to cool environmental temperatures. Fast growth and cool temperatures are primary triggers for PHS under most conditions of commercial broiler growout. In both experiments, final necropsies revealed higher RV:TV ratios in ascitic than in nonascitic broilers, whereas normalizing the left ventricle plus septum weight for differences in body weight generated similar values for ascitic and nonascitic males or females, respectively. These results support a primary role for pulmonary hypertension but not cardiomyopathy in the pathogenesis of ascites triggered by cool temperatures in both the Base and Resistant populations.

Evidence of mitochondrial dysfunction in broilers with pulmonary hypertension syndrome (Ascites): effect of t-butyl hydroperoxide on hepatic mitochondrial function, glutathione, and related thiols

The purpose of this study was to assess mitochondrial function and glutathione (a mitochondrial antioxidant) in response to oxidative stress in mitochondria in vitro obtained from broilers with and without pulmonary hypertension syndrome (PHS). Liver mitochondria from Control and PHS broilers were incubated with 0, 1, and 5-mM tertiary-butyl hydroperoxide (tBH). Indices of mitochondrial function [the respiratory control ratio (RCR) and the adenosine diphosphate to oxygen ratio (ADP:O)], and levels of mitochondrial and extra-mitochondrial reduced (GSH) and oxidized (GSSG) glutathione, cysteine, cystine, glutamate and cysteinyl-glycine were determined following tBH treatment. Lower RCR and ADP:O values were observed in PHS mitochondria than in controls. Whereas control mitochondria remained coupled (RCR > 2.0), only 3 PHS preparations remained coupled after 60 min of incubation with 5 mM tBH, indicating a greater susceptibility to oxidative stress in PHS mitochondria. The lower RCR in PHS mitochondria was due to increased oxygen consumption during State IV respiration. Oxidative stress following tBH treatment (decreased GSH and increased GSSG) was observed, but there were no differences in GSH or GSSG between control and PHS mitochondria. The PHS mitochondria did exhibit elevated mitochondrial and extramitochondrial cystine than controls, however. The results indicate that PHS mitochondria do not lack antioxidant protection from GSH, but lower RCR and ADP:O ratios in PHS mitochondria indicate a dysfunction that may contribute to the pathophysiology of this metabolic disease in broilers.

Influence of feed deprivation on ventilation and gas exchange in broilers: relationship to pulmonary hypertension syndrome

Fast-growing broiler chickens not uncommonly exhibit elevated pulmonary vascular resistance that leads to pulmonary hypertension and right ventricular failure. We tested the hypothesis that a distended gastrointestinal tract in these full-fed birds results in an abnormally low tidal volume and minute ventilation that could lead to pulmonary hypoxia, pulmonary arterial vasoconstriction, right ventricular failure, and ascites. Tidal volume, respiratory frequency, heart rate, percentage saturation of hemoglobin with oxygen (HbO2), O2 consumption, and carbon dioxide elimination were measured on fast-growing broiler chickens when full-fed and after 3, 6, and 9 h of feed deprivation. Tidal volume of full-fed birds was not abnormally low despite HbO2 values varying from above 80% to nearly 60%. Importantly, HbO2 was found to be markedly increased in the hypoxemic birds at and beyond a 3-h period without feed, despite a reduction in minute ventilation. This response was not caused by a decrease in O2 consumption. Thus, limitation of gas intake at the mouth was not the cause of the hypoxemia. The data suggest that feed deprivation results in an increase in parabronchial ventilation, possibly from improvement in aerodynamic valving, which would reduce pulmonary hypoxic vasoconstriction and right ventricular failure.

Metabolic disturbances in male broilers of different strains. 1. Performance, mortality, and right ventricular hypertrophy

Two trials were carried out to test the susceptibility for metabolic disturbances of different strains of male broilers. In Trial 1, 1,890 male chickens were allotted in a randomized block design with seven treatments (Arbor Acres, Avian Farms, Cobb-500, Hubbard-Peterson, ISA, Naked Neck, and Ross) and six blocks of 45 chickens. Trial 2 involved 2,184 male chickens of six strains (Arbor Acres, Avian Farms, Cobb 500, Hubbard-Peterson, ISA Naked Neck, and Ross) allotted in seven complete blocks of 52 birds. The same management system was adopted for all birds, reared up to 42 d in an open house during late winter (Trial 1) or late autumn (Trial 2). The most marked differences observed among the strains tested was the lower BW and higher feed conversion of Naked Neck broilers. Total percentage mortalities were high among the most productive broilers, being more than 50% due to sudden death (SDS) and ascites syndrome (AS). No Naked Neck birds died as a consequence of these disturbances and the total mortalities were significantly lower (P < or = 0.05) than the other strains. The ratio of right ventricle weight to total ventricle weight of the dead birds was over 0.25, except for Naked Neck birds, which presented a nonhypertrophic ratio. The two trials confirmed the relationship between high productivity and high incidence of SDS and AS and indicated that Naked Neck male broilers are resistant to these metabolic disturbances.

Evaluation of minimally invasive indices for predicting ascites susceptibility in three successive hatches of broilers exposed to cool temperatures

Broilers from three consecutive hatches were exposed to cool temperatures to amplify the incidence of pulmonary hypertension syndrome (PHS, ascites). The largest apparently healthy individuals on Day 42 were evaluated using minimally invasive diagnostic indices [percentage saturation of hemoglobin with oxygen, hematocrit (HCT), heart rate, electrocardiogram (ECG) Lead II, body weight), then they were subjected to the ongoing pressures of fast growth and cool temperatures to determine which of these indices are predictive of the subsequent onset of PHS. Approximately 20% of the males and females evaluated on Day 42 subsequently developed PHS by Day 51. When data for all hatches were pooled and broilers that subsequently developed ascites were compared with those that did not (nonascitic), body weights, heart rates, and percentage saturation of hemoglobin with oxygen were lower on Day 42 for ascitic than for nonascitic males, and HCT was higher in ascitic males and females than in nonascitic males and females, respectively. Comparisons of the ECG Lead II wave amplitudes for all hatches pooled indicated that RS-wave amplitude was larger in ascitic than in nonascitic males, and that S-wave amplitude was more negative in ascitic males and females than in nonascitic males and females. Necropsies conducted on Day 51 revealed higher right:total ventricular weight ratios in ascitic than in nonascitic broilers, whereas normalizing the left ventricle plus septum weight for differences in body weight generated similar values for ascitic and nonascitic males and females, respectively. These results support a primary role for pulmonary hypertension but not cardiomyopathy in the pathogenesis of ascites triggered by cool temperatures. Values obtained for minimally invasive diagnostic indices on Day 42 also establish predictive thresholds that can be used to evaluate the PHS susceptibility of large and apparently healthy male and female broilers.

Flow-dependent pulmonary vasodilation during acute unilateral pulmonary artery occlusion in Jungle Fowl

Giant Jungle Fowl previously were shown to be highly resistant to the onset of pulmonary hypertension syndrome (PHS, ascites) under conditions that induce a substantial incidence of PHS in broiler chickens. In the present study, lightly anesthetized, clinically healthy 12- to 13-wk-old male Giant Jungle Fowl maintained a lower respiratory rate, a similar hematocrit, and superior arterial blood gas values when compared with 6-wk-old male broilers. Giant Jungle Fowl weighed less than broilers (1,860 +/- 19 vs 2,788 +/- 63 g, respectively) and had equivalent absolute values for pulmonary arterial pressure, cardiac output, and pulmonary vascular resistance. Acute unilateral pulmonary artery occlusion in Giant Jungle Fowl doubled the pulmonary vascular resistance and forced the right ventricle to propel a sustained 60% increase in blood flow through the vasculature of the unoccluded lung. A transient increase in pulmonary arterial pressure initially was required to overcome the vascular resistance of the unoccluded lung; however, flow-dependent vasodilation gradually reduced the pulmonary vascular resistance and permitted pulmonary arterial pressure to return toward control levels. Unilateral pulmonary artery occlusion also triggered an immediate reduction in the partial pressure of oxygen in arterial blood, and the gradual return of pulmonary arterial pressure toward control levels did not eliminate this ventilation-perfusion mismatch, which has been attributed to blood flowing too rapidly through the unoccluded lung to permit diffusive gas equilibration. The inherent capacity for flow-dependent pulmonary vasodilation may reduce the susceptibility of Giant Jungle Fowl to PHS by reducing the increment in pulmonary arterial pressure required to propel an elevated blood flow through the lungs.

The infusion rate dependent influence of acute metabolic acidosis on pulmonary vascular resistance in broilers

Experiments were conducted to evaluate the pulmonary vascular responses of lightly anesthetized clinically healthy male broilers during acute metabolic acidosis induced by bolus i.v. injections or constant i.v. infusions of HCl. In Experiment 1, broilers received consecutive 1.5 mL i.v. bolus injections of 2.5% mannitol (volume control) and 0.4 N, 0.8 N, and 1.2 N HCl in 2.5% mannitol. Following each injection, equivalent concentrations of mannitol or HCl were infused i.v. at a rate of 0.05 mL/min.kg BW. In Experiment 2, repeated bolus injections of 2.5% mannitol and 1.2 N HCl were administered during ongoing constant infusion of 2.5% mannitol. The following variables were evaluated: pulmonary arterial pressure, pulmonary vascular resistance, mean arterial pressure, total peripheral resistance, cardiac output, stroke volume, heart rate, respiratory rate, hematocrit (HCT), and arterial blood gas (PaO2, PaCO2, pH, HCO3-). Mannitol alone did not alter any of the variables. The HCl loading protocols acidified the arterial blood to sustained (constant infusion) or transient (bolus injection) values averaging between pH 7.2 and 7.3. In both experiments, bolus injections of 1.2 N HCl caused transient increases in pulmonary vascular resistance and pulmonary arterial pressure, coincident with decreases in mean arterial pressure and cardiac output. When HCl was infused at a constant rate in Experiment 1, the arterial blood hydrogen ion concentration, [H+], was positively correlated with pulmonary arterial pressure and cardiac output, negatively correlated with mean arterial pressure and total peripheral resistance, and was not correlated with pulmonary vascular resistance. During constant i.v. infusion of mannitol or HCl in both experiments, pulmonary arterial pressure was positively correlated with pulmonary vascular resistance and cardiac output. Overall, bolus injections of 1.2 N HCl consistently triggered transient pulmonary vasoconstriction (increased pulmonary vascular resistance), leading to a transient increase in pulmonary arterial pressure in spite of opposing changes in cardiac output and mean arterial pressure. In contrast, equivalent or greater increases in [H+] during constant i.v. infusion of HCl caused a substantially lower increment in pulmonary arterial pressure, which, in, turn was primarily attributable to increases in cardiac output rather than pulmonary vascular resistance. Increments in either pulmonary vascular resistance or cardiac output induced by metabolic acidosis would be expected to contribute to the onset of pulmonary hypertension syndrome (PHS, ascites) in broilers.

Pathological changes in metabolism of poultry related to increasing production levels

A continuously increasing production level in poultry breeding has resulted in changes in metabolism. Selection procedures in breeding programmes are focused on an increase in growth rate and on a decrease in feed conversion ratio (less feed intake per unit of deposited tissue). These procedures do not pay attention to the maintenance requirements of birds. Imbalances between production (protein and fat deposition) and supply of energy for maintenance requirements lead to homeostatic dysregulation and to diseases of organs which supply the energy for production and maintenance. The alarming increase in metabolic diseases, such as heart failure syndrome, ascites, and oedema in the lungs and heart, can be directly related to an insufficient oxygen supply. A low oxygen consumption and heat production is one of the mechanisms by which a low feed conversion ratio can be achieved, as is induced hypothyroidism by which physical activity and thus heat production is reduced. Other diseases, such as liver cirrhosis, malabsorption syndrome, sudden death syndrome in broilers, and fatty liver-hemorrhage syndrome, which is nowadays the most important disease in laying hens in the Netherlands, can be related to an imbalance between the production rate and maintenance requirements. A continued selection on the basis of retained energy (in protein and fat) without paying attention to the maintenance requirements of birds will be detrimental for the health and welfare of poultry. These undesirable developments in poultry husbandry should be a challenge for sciences focused on welfare and stress in animals. Such a scientific approach to animals suffering from dysgenic changes in metabolism is needed to solve serious problems in poultry breeding.

Evaluation of logistic versus linear regression models for predicting pulmonary hypertension syndrome (ascites) using cold exposure or pulmonary artery clamp models in broilers

Syndromes such as ascites (pulmonary hypertension syndrome) present difficulties both in the interpretation of associated physiological observations and in their analyses. The ability to predict which physiological variables have the greatest influence on survival or, more importantly, which individuals are most susceptible or resistant to ascites would be very useful selection tools. When addressed in this manner, ascites data become binary data sets (healthy or affected). Binary data can be problematic in that they do not meet all of the assumptions necessary for more traditional analyses such as ANOVA and linear regression. Binary data are discrete and do not have normally distributed errors, which violates a fundamental assumption of linear models. The predictive abilities of linear and logistic regression were evaluated in two replicated experiments using two methods to induce ascites, cold exposure (COLD) and surgical clamping of one pulmonary artery (PAC). The logistic and linear predictive models were derived using the same data and variables. The first data set from PAC and COLD were used to develop the predictive models and the replicate data sets of PAC and COLD were used as "test data sets" for the prediction of ascites. The linear models developed were complex, using four or five variables and requiring up to seven different measurements. On average, the linear models predicted ascites correctly 87.6% of the time. The logistic models were simple (single variable) models that predicted ascites correctly 92.0% of the time. The variables used in the logistic models were derivations of the ratio of right ventricular weight to total ventricular weight, either corrected for age or the body weight of the bird. Although linear regression predicted the incidence of ascites almost as well as logistic regression did, logistic regression is the more appropriate test statistic to use.

Artificial neural network prediction of ascites in broilers

An artificial neural network was trained to predict the presence or absence of ascites in broiler chickens. The neural network was a three-layer back-propagation neural network with an input layer of 15 neurons (defining 15 physiological variables), a hidden layer of 16 neurons, and an output layer of 2 neurons (the presence or absence of ascites). Male by-products of a breeder pullet line were brooded at 32 and 30 C during Weeks 1 and 2, respectively. The training set for the neural network consisted of data from birds subjected to cool temperatures (18 C) to induce ascites. After training, the predictive ability of the neural network was verified with two new data sets. The second data set was from birds subjected to cool temperatures (18 C). The third data set was from birds subjected to clamping of the pulmonary artery to simulate the physiological processes involved in ascites (the temperature was 24 C). A comparison was made between laboratory diagnostic results and the neural network predicted ascites incidence. The neural network accurately identified the presence or absence of ascites in the first (training) set. Two false positives and one false positive were identified in the second and third verification sets, respectively. The birds identified as false positives were determined to be in the developmental stages of ascites before the occurrence of fluid accumulation. Artificial neural networks were found to effectively identify broilers with and without ascites.

Cardio-pulmonary function during acute unilateral occlusion of the pulmonary artery in broilers fed diets containing normal or high levels of arginine-HCl

Cardio-pulmonary function was measured in male broilers reared on diets formulated to contain 1.5% arginine (NORMAL group) or 2.5% arginine (ARGININE group). A snare placed around the right pulmonary artery permitted acute shunting of the entire cardiac output (CO) through the left pulmonary artery, resulting in sustained increases in blood flow (BF) through the left lung in both groups. The unilateral increase in BF was accompanied by sustained increases in pulmonary arterial pressure (PAP) and pulmonary vascular resistance (PVR) in the NORMAL group. However, following initial transient increases in PAP and PVR in the ARGININE group, subsequent pulmonary vasodilation gradually reduced PVR, and thus PAP, in spite of the ongoing elevation of BF through the left lung. The capacity of the pulmonary vasculature in the ARGININE group to accommodate an increased BF at a normal PAP accounts for the previously reported lower incidence of pulmonary hypertension syndrome (PHS, ascites) in cold-stressed broilers fed supplemental dietary arginine. Hypoxemia and respiratory acidosis ensued rapidly in both groups after tightening the pulmonary artery snare, in spite of a compensatory increase in the respiratory rate. The gradual return of PVR and PAP to presnare levels in the ARGININE group did not eliminate the concurrent ventilation-perfusion mismatch caused by the increased rate of BF through the left lung. Tightening the pulmonary artery snare caused mean systemic arterial pressure (MAP) to drop from control levels of approximately 98 mm Hg to sustained hypotensive levels of approximately 65 mm Hg in both groups. This systemic hypotension was caused by decreases in CO and total peripheral resistance (TPR). The reduction in CO were caused by reduction in stroke volume (SV) rather than heart rate (HR), suggesting that acutely tightening the pulmonary artery snare increased PVR sufficiently to impede left ventricular filling. Accordingly, the maximum increment in PAP attainable by the right ventricle during acute increases in PVR apparently was inadequate to propel the entire CO through the pulmonary vasculature, setting the stage for the congestive right-sided pooling of blood routinely associated with PHS in broilers.

Independent and simultaneous unilateral occlusion of the pulmonary artery and extra-pulmonary primary bronchus in broilers

Acutely tightening a snare around one pulmonary artery previously was shown to trigger a reversible ventilation-perfusion (V/Q) mismatch in broilers, as reflected by decreases in the partial pressure of oxygen in arterial blood (hypoxemia), accompanied by increases in the hydrogen ion concentration (acidosis) and partial pressure of carbon dioxide (hypercapnia). In the present study, snares were loosely implanted around the right pulmonary artery and the right extrapulmonary primary bronchus in anesthetized male broilers. These snares were tightened and released independently and then simultaneously to evaluate the possibility that directing the entire respiratory minute volume toward the left lung might attenuate the V/Q mismatch caused by forcing the entire cardiac output (CO) through the left lung. Fully reversible arterial blood hypoxemia, acidosis, and hypercapnia occurred when either snare was tightened independently. Presumably, tightening the bronchial snare restricted ventilation but not blood flow to the right lung, thereby permitting blood to perfuse poorly ventilated gas exchange surfaces. Simultaneously tightening both snares triggered arterial blood hypoxemia, acidosis, and hypercapnia similar to or greater in magnitude than the responses obtained by tightening the pulmonary artery snare independently. Tightening either snare independently or both snares simultaneously caused pulmonary arterial pressure to increase (pulmonary hypertension), and permanent obstruction of one bronchus in a separate experiment caused an increase in the right:total ventricular weight ratio, which is indicative of chronic pulmonary hypertension. The mean systemic arterial pressure decreased when the pulmonary artery snare was tightened independently or in combination with the bronchial snare, but not when the bronchial snare was tightened independently. The respiratory rate increased and the heart rate decreased when the pulmonary artery snare was tightened independently, but not when the bronchial snare was tightened independently or in combination with the pulmonary artery snare. These results demonstrate that the V/Q mismatch caused by forcing all the CO to perfuse one lung cannot be attenuated by simultaneously directing the entire respiratory minute volume toward the same lung.

Blood viscosity in broilers: influence on pulmonary hypertension syndrome

Elevation in apparent blood viscosity may enhance the pulmonary hypertension that leads to pulmonary hypertension syndrome (PHS) and ascites in fast-growing broilers. We investigated the importance of packed cell volume (PCV) and shear rate in modifying apparent viscosity of the blood from broilers assigned to normal, preascites, and ascites groups. Apparent viscosity of broiler blood increased at all shear rates as PCV increased; the increase in apparent viscosity became greater as the shear rate decreased at PCV above 0.30. At the PCV of normal broilers (0.30 or below), apparent viscosity was nearly shear rate independent, at least down to 11.25 per second, the lowest shear rate studied. Apparent viscosity, at any given PCV and shear rate, was significantly lower in the blood of birds with ascites than in normal birds; however, the relative viscosity was not different between those groups, indicating that lower plasma viscosity in the birds with PHS was responsible for the finding. The results show that the principal factor responsible for increased apparent viscosity of blood in birds with PHS is the increase in PCV. The increased resistance to flow of blood as the result of higher blood viscosity may contribute to the pulmonary hypertension.

Electrocardiographic evaluation of broilers during the onset of pulmonary hypertension initiated by unilateral pulmonary artery occlusion

Electrocardiography previously has been used as a noninvasive method for detecting cardiac hypertrophy associated with pulmonary hypertension syndrome (PHS, ascites). In the present study, 36 of 100 male broiler chicks were selected for inclusion in the experiment based on their hatch weight (> or = 40 g), Day 1 to 14 BW gain (upper 50% of population distribution), and the normalcy of their Day 14 electrocardiogram (ECG). On day 16, 10 chicks were assigned to the unoperated control group (CONTROL), sham operations were performed on 10 chicks (SHAM), and pulmonary hypertension was initiated by clamping the left pulmonary artery in 16 chicks (PA-CLAMP). Electrocardiogram leads I, II, III, and aVF were recorded daily until Day 27, when 6 of the 12 birds surviving in the PA-CLAMP group had developed clinical ascites. The right: total ventricular weight ratio (RV:TV) was higher and BW was lower in the PA-CLAMP group than in the CONTROL and SHAM groups on Day 27. The RS, R, and S wave amplitudes in lead II for the CONTROL and SHAM groups did not change, whereas in lead II for the PA-CLAMP group the S wave attained a more negative amplitude by Day 21, the RS wave attained a more negative amplitude by Day 22, and the R wave declined to a less positive amplitude by Day 23 when compared with presurgery values. Similar differences were observed for the RS and S waves for leads III and aVF. The mean electrical axis (MEA) and mean resultant vector (MRV) of the CONTROL and SHAM groups did not change; however the PA-CLAMP group the MEA rotated significantly from +3 degrees to -72 degrees and to -88 degrees on Days 14, 22 and 27, respectively, and the MRV amplitude increased from 0.052 to 0.108 mV and then to 0.179 mV on Days 14, 22, and 27, respectively. When data from all treatment groups were combined, higher absolute and BW-normalized RV:TV ratios were inversely correlated (r = 0.859 to -0.880) with increasingly negative S wave amplitudes in leads II and aVF. Higher absolute and BW-normalized RV:TV ratios were directly correlated (r = 0.786 to 0.789) with increasing MRV amplitudes. These ECG characteristics constitute accurate, noninvasive predictive criteria suitable for detecting cardiac changes occurring early during the onset of primary pulmonary hypertension.

Does pulmonary hypertension syndrome (ascites) occur more frequently in broilers medicated with monensin?

The performance of broilers reared in floor pens and given monensin in the feed at 121 ppm was compared with that of birds given no drug. Feed intake and BW gain of medicated birds was significantly lower than that of unmedicated birds from 0 to 22 d of age. Feed intake and feed conversion of medicated birds was significantly reduced, compared with unmedicated birds, from 22 to 53 and 0 to 60 d of age. Total mortality, and mortality due to leg abnormalities from 22 to 53 and 0 to 60 d, was significantly lower in birds given monensin. There was no difference in the incidence of tibial dyschondroplasia (TD) by 60 d. No differences in mortality due to pulmonary hypertension syndrome (PHS) were observed for any age period. Birds removed from pens at 28 d that had received monensin had lower hematocrit and percentage saturation of hemoglobin with oxygen in the blood than unmedicated birds. No differences in these variables were found at 54 d. There were no differences in the right ventricle weight: total ventricular weight ratios or electrocardiogram lead II values at 28 or 54 d. The results indicate that PHS does not occur more frequently in broilers medicated with monensin.

Effect of alpha-tocopherol on antioxidants, lipid peroxidation, and the incidence of pulmonary hypertension syndrome (ascites) in broilers

Research has demonstrated a compromised antioxidant capacity in broilers with pulmonary hypertension syndrome (PHS). Thus, the objective of the present study was to assess the effects of vitamin E on PHS-induced mortality, tissue antioxidants, and plasma lipid peroxides in male broilers. Control broilers were provided normal ventilation but others, maintained under low ventilation conditions to induce PHS, were randomly assigned to nonimplanted (NI), placebo (PL), or vitamin E (VE) implanted groups. The VE implant released a total of 15 mg of alpha-tocopherol from 0 to 3 wk of age. Tissues and blood samples were obtained at 3 and 5 wk of age from birds with (PHS+) and without (PHS-) PHS. Five-week PHS cumulative mortality was lowered by alpha-tocopherol with mortality rates of 3.6, 4.2, 11.9, and 11.8%, for Controls, VE, NI, and PL groups, respectively. The PHS+ birds exhibited lower body weights, higher hematocrit, right ventricular hypertrophy, lower alpha-tocopherol and glutathione (GSH) concentrations in liver and lung, as well as indicators of oxidative stress, including elevated plasma lipid peroxides and lower oxidized GSH in liver and erythrocytes, at 5 wk of age. All birds exhibited lower erythrocyte catalase activity at 5 than at 3 wk of age. An improved antioxidant capacity was observed in VE birds, including higher liver and lung alpha-tocopherol at 3 and 5 wk, higher liver GSH at 3 wk, and lower plasma lipid peroxide values at 5 wk of age. Direct correlations observed between body weight and plasma lipid peroxides at 3 wk (r = .45) and between right ventricular hypertrophy and plasma lipid peroxides at 5 wk (r = .48), suggests that lipid peroxidation plays a role in the etiology of PHS. The results indicate that the VE implant was effective in lowering PHS-induced mortality in broilers apparently by attenuating processes leading to lipid peroxidation.

Evidence of a ventilation-perfusion mismatch during acute unilateral pulmonary artery occlusion in broilers

A ventilation-perfusion (V/Q) mismatch can be diagnosed when a moderate increase in cardiac output (CO) causes systemic hypoxemia, thereby exposing a pulmonary incapacity to fully oxygenate the additional blood flowing through the pulmonary vasculature. The susceptibility of broiler chickens to hypoxemia was evaluated in lightly anesthetized, clinically healthy, 40- to 49-d-old males. A snare placed around one pulmonary artery permitted acute, reversible shunting of the entire CO through the unobstructed lung. Blood samples were withdrawn from arterial and venous cannulas for blood gas analysis, and a pulse oximeter was used for noninvasive measurements of the percentage saturation of hemoglobin with oxygen in arterialized capillary beds. The partial pressure of oxygen in arterial blood averaged 103 mm Hg during control periods, 79 mm Hg (hypoxemia) when the pulmonary artery snare was tightened for 12 min, and 101 mm Hg within 5 min after releasing the snare. The percentage saturation of hemoglobin with oxygen before, during, and after tightening the snare averaged, respectively, 96, 91, and 96% for arterial blood, 81, 55, and 78% for venous blood, and 87, 67, and 88% for arterialized capillary beds. Tightening the snare increased the partial pressure of carbon dioxide and the hydrogen ion concentration above control levels in both arterial and venous blood, and these variables returned to control levels upon release of the snare. The combined data constitute direct evidence that clinically healthy broiler chickens are susceptible to hypoxemia during an acute moderate (approximately twofold) increase in pulmonary blood flow.

A pulmonary artery clamp model for inducing pulmonary hypertension syndrome (ascites) in broilers

Two experiments were conducted to test the hypothesis that a primary increase in pulmonary vascular resistance can initiate a pathophysiological progression leading to pulmonary hypertension syndrome (PHS, ascites). Pulmonary vascular resistance was increased by surgically clamping the left pulmonary artery when male broiler chicks were 15 to 19 d of age, resulting in a 90% incidence of PHS in Experiment 1, and a 68% incidence of PHS in Experiment 2. The incidence of PHS was 8% for control or sham-operated broilers in Experiment 1, whereas in Experiment 2 no (0%) PHS occurred in sham-operated broilers or in individuals with a pulmonary artery that only was partially occluded. Broilers with a fully occluded left pulmonary artery developed pulmonary hypertension, as demonstrated by increased right:total ventricular weight ratios (right ventricular hypertrophy) and by increased electrocardiogram lead II R-S wave amplitudes (generalized ventricular dilation and hypertrophy). Forcing the entire cardiac output through the right lung resulted in a lower percentage saturation of hemoglobin with oxygen and an elevated hematocrit, reflecting generalized systemic hypoxemia. Pulmonary hypertension and hypoxemia also were specifically characteristic of all birds that developed ascites, regardless of treatment group. These observations demonstrate for the first time that PHS (ascites) can be directly induced by a primary increase in pulmonary vascular resistance. The observed changes in percentage saturation of hemoglobin with oxygen suggest that the lungs of broilers may be unable to efficiently oxygenate the blood when forced to receive an increased cardiac output at an elevated pulmonary arterial pressure.

Changes in pulmonary arterial and femoral arterial blood pressure upon acute exposure to hypobaric hypoxia in broiler chickens

An experiment was conducted to investigate the pulmonary arterial and femoral arterial pressure responses to acute hypobaric hypoxia. Twenty-four, 7-wk-old Hubbard x Hubbard male chickens were lightly anesthetized and catheters were introduced into the right femoral artery and the pulmonary artery. The birds were then placed in a hypobaric chamber, and blood pressure responses were monitored during acute (15 min) exposures to simulated altitudes of 2,000 and 4,000 m. The pulmonary artery pressure increased .7 and 4% during the first and second exposures to a simulated altitude of 2,000 m, whereas the femoral artery pressure decreased 6 and 8% during exposures to this altitude. The pulmonary artery pressure increased 7% on the first exposure and 23% (P < .05) on the second exposure to a simulated altitude of 4,000 m. The femoral arterial pressure decreased (P < .05) on both exposures to this altitude (29 and 24%, respectively). The initial femoral and pulmonary artery pressures and changes in these pressures upon exposure to hypobaric hypoxia were not consistently correlated with the characteristics of the electrocardiogram, packed cell volume, body weight, or the right:total ventricular weight ratio. These results indicate that acute hypobaric hypoxia elicits a hypotensive response in the systemic arterial circulation and a hypertensive response in the pulmonary arterial circulation of broiler chickens.(ABSTRACT TRUNCATED AT 250 WORDS)

Furosemide reduces the incidence of pulmonary hypertension syndrome (ascites) in broilers exposed to cool environmental temperatures

The incidence of pulmonary hypertension syndrome (PHS; ascites) was evaluated in two experiments using broiler breeder male by-product chicks exposed after 3 wk of age to cool environmental temperatures (10 to 15 C). In Experiment 1, 3- to 6-wk-old birds were fed a grower diet to which 0 (Control), .001, .005, .010, or .015% furosemide had been added. All groups in Experiment 1 were fed a finisher ration containing no furosemide during Weeks 7 to 8. In Experiment 2, the Control group received no furosemide, a second group received .015% furosemide during the grower phase only (Weeks 3 to 6), and the third group received .015% furosemide during the grower and finisher phases (Weeks 3 to 8). Cumulative PHS mortality was significantly reduced by furosemide in both experiments. Compared with Controls, birds fed .015% furosemide did not have lower (P = .077) final body weights in Experiment 1 but did have significantly lower final body weights in Experiment 2. Lower levels of furosemide significantly reduced PHS mortality without reducing body weights. Furosemide did not improve feed conversion in either experiment. Neither body weight on Day 1 or 21 nor net Day 1 to 21 weight gain were predictive of susceptibility to PHS during the subsequent grower and finisher intervals in either experiment. On Day 55 of Experiment 2, large healthy birds fed .015% furosemide had significantly lower right:total ventricular weight ratios than control birds, indicating that furosemide reduced right ventricular hypertrophy, presumably by reducing pulmonary arterial pressure.

Ultrastructural demonstration of mitochondrial calcium overload in myocardial cells from broiler chickens with ascites and induced hypoxia

Two groups of young broiler chickens, namely, naturally occurring field cases of ascites and those with an induced hypoxia, were used in an ultrastructural study to examine the localisation and distribution of intracellular Ca2+ in cardiomyocytes. Age-matched healthy flockmates were used to control each group. Deposits of Ca2+ were located extensively in the mitochondria, sarcoplasmic reticulum and Golgi apparatus and sometimes in the myocyte and endothelial cell nuclei of both groups of birds. The results suggest that the cells from the hearts of the ascitic broilers may have been exposed to hypoxia since a large proportion of control material showed no Ca2+ activity in either mitochondria or nuclei. The presence of a Ca2+ overload in the mitochondria of cardiomyocytes from ascitic birds reared at low altitude or sea level suggests that these broilers were suffering from the deleterious effects of chronic hypoxia due to poor or reduced oxygen use.

Improved arterial oxygenation with feed restriction in rapidly growing broiler chickens

1. Rapidly growing broiler chickens fed ad lib. until 56 days, but feed restricted until 60 days of age, had higher arterial oxygen saturations, lower respiratory frequencies, total ventilations that were not different, and higher tidal volumes compared to those fully fed for 56 days. 2. Arterial oxygen saturation correlated negatively with respiratory frequency, but was not related to total ventilation or tidal volume. 3. Hypoventilation appeared not to be the cause of arterial oxygen desaturation. 4. Arterial oxygen desaturation correlated with the degree of right ventricular hypertrophy.