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

Physiological parameter values for physiologically based pharmacokinetic models in food-producing animals. Part II: Chicken and turkey

Physiologically based pharmacokinetic (PBPK) models are growing in popularity due to human food safety concerns and for estimating drug residue distribution and estimating withdrawal intervals for veterinary products originating from livestock species. This paper focuses on the physiological and anatomical data, including cardiac output, organ weight, and blood flow values, needed for PBPK modeling applications for avian species commonly consumed in the poultry market. Experimental and field studies from 1940 to 2019 for broiler chickens (1-70 days old, 40 g - 3.2 kg), laying hens (4-15 months old, 1.1-2.0 kg), and turkeys (1 day-14 months old, 60 g -12.7 kg) were searched systematically using PubMed, Google Scholar, ProQuest, and ScienceDirect for data collection in 2019 and 2020. Relevant data were extracted from the literature with mean and standard deviation (SD) being calculated and compiled in tables of relative organ weights (% of body weight) and relative blood flows (% of cardiac output). Trends of organ or tissue weight growth during different life stages were calculated when sufficient data were available. These compiled data sets facilitate future PBPK model development and applications, especially in estimating chemical residue concentrations in edible tissues to calculate food safety withdrawal intervals for poultry.

Effects of carbon dioxide on turkey poult performance and behavior

Appropriate ventilation of poultry facilities is critical for achieving optimum performance. Ventilation promotes good air exchange to remove harmful gases, excessive heat, moisture, and particulate matter. In a turkey brooder barn, carbon dioxide (CO2) may be present at higher levels during the winter due to reduced ventilation rates to maintain high temperatures. This higher CO2 may negatively affect turkey poult performance. Therefore, the objective of this study was to evaluate the effects of subjecting tom turkey poults (commercial Large White Hybrid Converters) to different constant levels of atmospheric CO2 on their growth performance and behavior. In three consecutive replicate trials, a total of 552 poults were weighed post-hatch and randomly placed in 3 environmental control chambers, with 60 (Trial 1) and 62 (Trials 2 and 3) poults housed per chamber. They were reared with standard temperature and humidity levels for 3 wks. The poults were exposed to 3 different fixed CO2 concentrations of 2,000, 4,000, and 6,000 ppm throughout each trial. Following each trial (replicate), the CO2 treatments were switched and assigned to a different chamber in order to expose each treatment to each chamber. At the end of each trial, all poults were sent to a local turkey producer to finish growout. For each trial, individual body weight and group feed intake were measured, and mortality and behavioral movement were recorded. Wk 3 and cumulative body weight gain of poults housed at 2,000 ppm CO2 was greater (P < 0.05) than those exposed to 4,000 and 6,000 ppm CO2. Feed intake and feed conversion were unaffected by the different CO2 concentrations. No significant difference in poult mortality was found between treatments. In addition, no effect of CO2 treatments was evident in the incidence of spontaneous turkey cardiomyopathy for turkeys processed at 19 wk of age. Poults housed at the lower CO2 level (2,000 ppm) demonstrated reduced movement compared with those exposed to the 2 higher CO2 concentrations.

Pulmonary arterial hypertension (ascites syndrome) in broilers: a review

Pulmonary arterial hypertension (PAH) syndrome in broilers (also known as ascites syndrome and pulmonary hypertension syndrome) can be attributed to imbalances between cardiac output and the anatomical capacity of the pulmonary vasculature to accommodate ever-increasing rates of blood flow, as well as to an inappropriately elevated tone (degree of constriction) maintained by the pulmonary arterioles. Comparisons of PAH-susceptible and PAH-resistant broilers do not consistently reveal differences in cardiac output, but PAH-susceptible broilers consistently have higher pulmonary arterial pressures and pulmonary vascular resistances compared with PAH-resistant broilers. Efforts clarify the causes of excessive pulmonary vascular resistance have focused on evaluating the roles of chemical mediators of vasoconstriction and vasodilation, as well as on pathological (structural) changes occurring within the pulmonary arterioles (e.g., vascular remodeling and pathology) during the pathogenesis of PAH. The objectives of this review are to (1) summarize the pathophysiological progression initiated by the onset of pulmonary hypertension and culminating in terminal ascites; (2) review recent information regarding the factors contributing to excessively elevated resistance to blood flow through the lungs; (3) assess the role of the immune system during the pathogenesis of PAH; and (4) present new insights into the genetic basis of PAH. The cumulative evidence attributes the elevated pulmonary vascular resistance in PAH-susceptible broilers to an anatomically inadequate pulmonary vascular capacity, to excessive vascular tone reflecting the dominance of pulmonary vasoconstrictors over vasodilators, and to vascular pathology elicited by excessive hemodynamic stress. Emerging evidence also demonstrates that the pathogenesis of PAH includes characteristics of an inflammatory/autoimmune disease involving multifactorial genetic, environmental, and immune system components. Pulmonary arterial hypertension susceptibility appears to be multigenic and may be manifested in aberrant stress sensitivity, function, and regulation of pulmonary vascular tissue components, as well as aberrant activities of innate and adaptive immune system components. Major genetic influences and high heritabilities for PAH susceptibility have been demonstrated by numerous investigators. Selection pressures rigorously focused to challenge the pulmonary vascular capacity readily expose the genetic basis for spontaneous PAH in broilers. Chromosomal mapping continues to identify regions associated with ascites susceptibility, and candidate genes have been identified. Ongoing immunological and genomic investigations are likely to continue generating important new knowledge regarding the fundamental biological bases for the PAH/ascites syndrome.

Physiological, management and environmental triggers of the ascites syndrome: a review

In meat-type chickens, an inadequacy of vascular capacity for blood flow through the lung to provide the tissues with the oxygen needed for rapid growth is the primary cause of pulmonary hypertensioninduced ascites. There are a variety of other factors that can trigger the ascites syndrome. These factors may cause increased blood flow because of a higher metabolic rate (cold, heat, certain nutrients, chemicals, etc.) or they may cause pulmonary hypertension-induced ascites in rapidly growing chickens because of greater resistance to blood flow in the lung by: (i) increased blood viscosity or red blood cell rigidity; or (ii) reduced vascular capacity in the lung. Some secondary factors, such as high sodium from salt in feed or water, may cause both increased flow and increased resistance to flow. Measures to reduce the ascites syndrome must address the primary genetic cause of insufficient vascular flow capacity in the lung and oxygen delivery to tissues, and the secondary factors that increase oxygen requirement, blood flow and the resistance to blood flow in the lung.

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.

Blood gas values and pulmonary hypertension as affected by dietary sodium source in broiler chickens reared at cool temperature in a high-altitude area

One hundred and twenty day-old male chicks (Ross 308) reared at a cool temperature at high altitude were subjected to the following two treatments in a completely randomised design: (1) a group for which the sodium requirements were supplied by sodium chloride from day-old age and regarded as control, (2) a group similar to the control but for which 50% of the sodium requirements was supplied by sodium bicarbonate from day-old age. Provision of sodium equally from NaCl and NaHCO₃ significantly (P < 0.05) increased the partial pressure of oxygen and the saturation of haemoglobin with oxygen, and significantly (P < 0.05) decreased the heterophil to lymphocyte ratio. The right ventricle to total ventricles ratio shifted to lower values as a result of substituting NaHCO₃ for NaCl as a sodium source. Growth performance and carcass characteristics were not affected significantly by the dietary sodium source.

Partial pressure of carbon dioxide in the venous blood of young birds as a predictor of ascites susceptibility in broiler chickens

In order to investigate the relationship between carbon dioxide tensions in the venous blood of young chickens and ascites susceptibility, one hundred day-old chickens from two pure broiler breeder lines differing in susceptibility to ascites syndrome were obtained and reared at low environmental temperature. Weekly, blood samples were taken for the determination of blood gas parameters and plasma thyroid hormone levels. Dead birds were examined for lesions of ascites daily and all survived birds were autopsied at the end of the trials. In cold conditioning, the cumulative incidence of right ventricular hypertrophy (RVH) and ascites was 78% (39/50) in fast-growing (line A) and 50% (25/50) in slow-growing (line B) chickens, confirming that line A chickens had higher susceptibility to ascites than line B chickens. At 12 days of age, the mean pCO(2) tension was significantly (P < 0.01) higher in the venous blood of line A than line B chickens. During the experiment, the majority of line A and line B chickens showing RVH and ascites exhibited pCO(2) tensions equal to, or exceeding 50 mmHg at 12 days of age. Additionally, fast-growing chickens showed significantly lower plasma T3 and T4 concentrations than slow-growing chickens. In conclusion, our data indicate that carbon dioxide pressure in the venous blood of early postnatal broiler chickens could be used as a valuable predictor in the selection of birds susceptible to pulmonary hypertension and ascites. The function of thyroid hormones should also be taken into consideration in further selection procedures for meat-type chickens.

Transpulmonary pressure gradient verifies pulmonary hypertension is initiated by increased arterial resistance in broilers

Previous hemodynamic evaluations demonstrated that pulmonary arterial pressure (PAP) is higher in broilers that are susceptible to pulmonary hypertension syndrome (PHS, ascites) than in broilers that are resistant to PHS. We compared key pulmonary hemodynamic parameters in broilers from PHS-susceptible and PHS-resistant lines (selected for 12 generations under hypobaric hypoxia) and in broilers from a relaxed (control) line. In experiment 1 the PAP was measured in male broilers in which a flow probe positioned on one pulmonary artery permitted the determination of cardiac output and pulmonary vascular resistance (PVR). The PAP and relative PVR were higher in susceptible broilers than in relaxed and resistant broilers, whereas absolute and relative cardiac output did not differ between lines. In experiment 2 male and female broilers from the 3 lines were catheterized to measure pressures in the wing vein, right atrium, right ventricle, pulmonary artery, and pulmonary veins (WP, wedge pressure). The transpulmonary pressure gradient (TPG) was calculated as (PAP-WP), with PAP quantifying precapillary pressure and WP approximating postcapillary pulmonary venous pressure. When compared with resistant and relaxed broilers, PAP values in susceptible broilers were > or =10 mmHg higher, TPG values were > or =8 mmHg higher, and WP values were < or =2 mmHg higher, regardless of sex. The combined hemodynamic criteria (elevated PAP and PVR combined with a proportionally elevated TPG) demonstrate that susceptibility to PHS can be attributed primarily to pulmonary arterial hypertension associated with increased precapillary (arteriole) resistance rather than to pulmonary venous hypertension caused by elevated postcapillary (venous and left atrial) resistance.

An inadequate pulmonary vascular capacity and susceptibility to pulmonary arterial hypertension in broilers

Broilers are susceptible to pulmonary hypertension syndrome (PHS; ascites syndrome) when their pulmonary vascular capacity is anatomically or functionally inadequate to accommodate the requisite cardiac output without an excessive elevation in pulmonary arterial pressure. The consequences of an inadequate pulmonary vascular capacity have been demonstrated experimentally and include elevated pulmonary vascular resistance (PVR) attributable to noncompliant, fully engorged vascular channels; sustained pulmonary arterial hypertension (PAH); systemic hypoxemia and hypercapnia; specific right ventricular hypertrophy, and right atrioventricular valve failure (regurgitation), leading to central venous hypertension and hepatic cirrhosis. Pulmonary vascular capacity is broadly defined to encompass anatomical constraints related to the compliance and effective volume of blood vessels, as well as functional limitations related to the tone (degree of constriction) maintained by the primary resistance vessels (arterioles) within the lungs. Surgical occlusion of 1 pulmonary artery halves the anatomical pulmonary vascular capacity, doubles the PVR, triggers PAH, eliminates PHS-susceptible broilers, and reveals PHS-resistant survivors whose lungs are innately capable of handling sustained increases in pulmonary arterial pressure and cardiac output. We currently are using i.v. microparticle injections to increase the PVR and trigger PAH sufficient in magnitude to eliminate PHS-susceptible individuals while allowing PHS-resistant individuals to survive as progenitors of robust broiler lines. The microparticles obstruct pulmonary arterioles and cause local tissues and responding leukocytes to release vasoactive substances, including the vasodilator NO and the highly effective vasoconstrictors thromboxane A(2) and serotonin [5-hydroxytryptamine (5-HT)]. Nitric oxide is the principal vasodilator responsible for modulating (attenuating) the PAH response and ensuing mortality triggered by i.v. microparticle injections, whereas microparticle-induced increases in PVR can be attributed principally to 5-HT. Our observations support the hypothesis that susceptibility to PHS is a consequence of anatomically inadequate pulmonary vascular capacity combined with the functional predominance of the vasoconstrictor 5-HT over the vasodilator NO. The contribution of TxA(2) remains to be determined. Selecting broiler lines for resistance to PHS depends upon improving both anatomical and functional components of pulmonary vascular capacity.

Evaluation of Growth Rate, Body Weight, Heart Rate, and Blood Parameters as Potential Indicators for Selection Against Susceptibility to the Ascites Syndrome in Young Broilers

The continuous selection for rapid growth has been accompanied by an increasing occurrence of ascites syndrome (AS), which develops in broilers failing to supply the increasing demand for O(2) in their bodies. Moderate heritability has been reported for AS in broiler populations, suggesting that selection against AS is feasible. However, direct selection based on AS mortality requires exposure of candidate birds to AS-inducing conditions (AIC), which hinder selection for performance traits. Noninvasive indicators of AS, expressed under standard husbandry, may facilitate the integration of selection against AS into breeding programs. This study was designed to look for differences in heart rate, hematocrit, O(2) saturation of hemoglobin in arterial blood (SaO(2)), BW, and weight gain, all measured at early ages under standard brooding conditions, between birds that later developed AS and those that remained healthy under AIC, and to estimate the heritability of these AS-related parameters and their genetic correlation with the tendency of broilers to develop AS. The experimental population was derived from a broiler dam line. Male progeny of 34 half-sib sire families were reared under standard brooding conditions to 19 d of age, then under an AIC protocol consisting of housing in individual cages, cool air high-speed ventilation, and growth enhancement using high-energy pelleted feed and 23 h/d of light. Birds were necropsied upon mortality or at the end of the trials and were recorded as being susceptible, with manifestations of AS (SUS), or resistant and healthy (RES). About 44% developed AS, confirming the efficacy of the novel AIC protocol. The SUS and RES chicks did not differ in BW and weight gain up to 19 d of age, suggesting that there was no association between AS susceptibility and rapid early growth. The SUS chicks exhibited lower SaO(2) and heart rate than the RES chicks. Moderate heritability was estimated for all traits, but only SaO(2) exhibited consistently significant genetic correlation (-0.5) with AS, suggesting that it may serve as an early indicator for selection against AS, albeit with a limited efficacy.

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.

Influence of aminoguanidine, an inhibitor of inducible nitric oxide synthase, on the pulmonary hypertensive response to microparticle injections in broilers

The pulmonary hypertensive response to pulmonary vascular obstruction caused by intravenously injected microparticles is amplified by pretreatment with N(omega)nitro-L-arginine methyl ester (L-NAME). The L-NAME prevents the synthesis of the potent vasodilator nitric oxide (NO) by inhibiting both the constitutive [endothelial NO synthase (eNOS or NOS-3)] and inducible [inducible NO synthase (iNOS or NOS-2)] forms of NO synthase. In the present study we used the selective iNOS inhibitor aminoguanidine (AG) to evaluate the role of iNOS in modulating the pulmonary hypertension (PH) triggered by microparticle injections. Experiment 1 was conducted to confirm the ability of AG to inhibit NO synthesis by iNOS in broiler peripheral blood mononuclear cells exposed to bacterial lipopolysaccharide (LPS, endotoxin). Mononuclear leukocytes treated with LPS produced 10-fold more NO than untreated (control) cells. The LPS-stimulated production of NO was partially inhibited by L-NAME and was fully inhibited by AG, thereby confirming that AG inhibits LPS-mediated iNOS activation in broilers. In Experiment 2 we evaluated the responses of male progeny from a base population (MP Base) and from a derivative line selected for one generation from the survivors of an LD50 microparticle injection (MP Select). The pulmonary arterial pressure (PAP) was lower in MP Select than in MP Base broilers. Both lines exhibited similar percentage increases in PAP after microparticles were injected, and AG modestly amplified the PH triggered by microparticles in both lines. In Experiment 3 we evaluated the responses of male progeny from a second base population (PAC Base) and from a derivative line selected for 3 generations using the unilateral pulmonary artery clamp technique (PAC Select). The PAP was lower in PAC Select than in PAC Base broilers, and both lines exhibited similar percentage increases in PAP in response to the microparticles. The PH triggered by microparticles was not amplified by AG but was doubled by L-NAME. These experiments demonstrate that during the 30 min following pulmonary vascular entrapment of microparticles, iNOS modulated the PH elicited in broilers derived from the MP pedigree line, but not in broilers from the PAC pedigree line. Different NOS-mediated responses among broiler populations may affect pulmonary hemodynamic characteristics of broiler lines selected using i.v. microparticle injections.

Pulmonary hypertension triggered by lipopolysaccharide in ascites-susceptible and -resistant broilers is not amplified by aminoguanidine, a specific inhibitor of inducible nitric oxide synthase

Nitric oxide (NO) is a potent pulmonary vasodilator that modulates the pulmonary vasoconstriction and pulmonary hypertension (PH) triggered by bacterial lipopolysaccharide (LPS) in broilers. The amplitude and duration of the LPS-induced PH are markedly enhanced following pretreatment with N(omega)-nitro-L-arginine methyl ester (L-NAME), which inhibits NO synthesis by both the constitutive (endothelial) and inducible (inflammatory) forms of nitric oxide synthase (eNOS and iNOS, respectively). In the present study L-NAME and the selective iNOS inhibitor aminoguanidine (AG) were administered to differentiate between iNOS and eNOS as the primary source of NO that attenuates the pulmonary vascular response to LPS. Clinically healthy male progeny from ascites-susceptible and ascites-resistant lines were anesthetized, and their pulmonary artery was cannulated. The initial pulmonary arterial pressure (PAP) was recorded, then the broilers either remained untreated (control group) or were injected i.v. with AG. Ten minutes later all birds received an i.v. injection of LPS, followed 40 min later by an i.v. injection of L-NAME. When compared with untreated controls, AG neither increased the baseline PAP nor did it increase or prolong the PH response to LPS. The ascites-susceptible broilers maintained a higher PAP than the ascites-resistant broilers throughout the experiment, and the ascites-resistant broilers exhibited greater relative increases in PAP in response to LPS than did the ascites-susceptible broilers. Within 40 min after the LPS injection, PAP subsided to a level that did not differ from the respective preinjection value for each line. Injecting L-NAME reversed the decline in PAP, and within 5 min PAP returned to hypertensive levels approaching the maximum peak PH response to LPS. The absence of any impact of AG coupled with the profound response to L-NAME indicates that NO synthesized by eNOS rather than iNOS likely modulated the acute (within 1 h) PH elicited by LPS. Evidently eNOS is activated by the increased shear stress exerted on the endothelium during the PH response to LPS, whereas LPS-mediated up-regulation of iNOS expression may take longer than 1 h before biologically effective quantities of NO are produced.

Nω-nitro-L-arginine methyl ester (L-NAME) amplifies the pulmonary hypertensive response to microparticle injections in broilers

We tested the hypothesis that microparticles entrapped within the pulmonary vasculature elicit the production of nitric oxide (NO) in quantities sufficient to modulate the combined impact of physical occlusion plus contemporaneously released vasoconstrictors. In experiment 1, male broilers were given an injection of the NO synthase (NOS) inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME), followed by an intravenous injection of cellulose microparticles while the pulmonary arterial pressure (PAP) and cardiac output (CO) were recorded. When L-NAME was used to block NO synthesis induced by the microparticles, an early peak of pulmonary hypertension was revealed that rarely developed in the absence of L-NAME. The subsequent more prolonged increases in PAP and pulmonary vascular resistance (PVR) were greater in amplitude and duration in broilers pretreated with L-NAME than in broilers in the control group. These amplified responses occurred in spite of a simultaneous reduction in CO, thereby conclusively demonstrating that inhibiting NOS permitted the development of a much more profound increase in the PVR. In experiment 2 the mortality triggered within 48 h after injecting microparticles was evaluated in the presence and absence of L-NAME. The 48 h postinjection mortality more than doubled when L-NAME was combined with microparticle injection doses that otherwise caused relatively low mortality in the absence of L-NAME. Experiment 3 was conducted to determine whether NO contributes to the systemic hypoxemia that develops after microparticles are injected. L-NAME administration had no impact on the magnitude and duration of the microparticle induced decline in the percentage saturation of hemoglobin with oxygen (%HbO2). Evidently hypoxemia per se contributes relatively little to the amplified pulmonary vasoconstriction and 48 h postinjection mortality triggered by microparticle injections in broilers pretreated with L-NAME. These observations indicate that NO modulates the responses to vasoconstrictors released when microparticles become entrapped in the pulmonary vasculature. Inhibition of NOS by L-NAME exposed a more dramatic increase in PVR and pulmonary hypertension leading to enhanced mortality in response to microparticle injections.

Major histocompatibility (B) complex control of responses against Rous sarcomas

The chicken major histocompatibility (B) complex (MHC) affects disease outcome significantly. One of the best characterized systems of MHC control is the response to the oncogenic retrovirus, Rous sarcoma virus (RSV). Genetic selection altered the tumor growth pattern, either regressively or progressively, with the data suggesting control by one or a few loci. Particular MHC genotypes determine RSV tumor regression or progression indicating the crucial B complex role in Rous sarcoma outcome. Analysis of inbred lines, their crosses, congenic lines, and noninbred populations has revealed the anti-RSV response of many B complex haplotypes. Tumor growth disparity among lines identical at the MHC but differing in their background genes suggested a non-MHC gene contribution to tumor fate. Genetic complementation in tumor growth has also been demonstrated for MHC and non-MHC genes. RSV tumor expansion reflects both tumor cell proliferation and viral replication generating new tumor cells. In addition, the B complex controls tumor growth induced by a subviral DNA construct encoding only the RSV v-src oncogene. Immunity to subsequent tumors and metastasis also exhibit MHC control. Genotypes that regressed either RSV or v-src DNA primary tumors had enhanced protection against subsequent homologous challenge. Regressor B genotypes had lower tumor metastasis compared with progressor types. Together, the data indicate that B complex control of RSV tumor fate is strongly defined by the response to a v-src-determined function. Differential RSV tumor outcomes among various B genotypes may include immune recognition of a tumor-specific antigen or immune system influences on viral replication.

Dietary sodium bicarbonate, cool temperatures, and feed withdrawal: impact on arterial and venous blood-gas values in broilers

Sodium bicarbonate (NaHCO3) has been used successfully in mammals and birds to alleviate pulmonary hypertension. Experiment 1 was designed to provide measurements of arterial and venous blood-gas values from unanesthetized male broilers subjected to a cool temperature (16 degrees C) challenge and fed either a control diet or the same diet alkalinized by dilution with 1% NaHCO3. The incidences of pulmonary hypertension syndrome (PHS, ascites) for broilers fed the control or bicarbonate diets were 15.5 and 10.5%, respectively (P = 0.36, NS). Non-ascitic broilers fed the control diet were heavier than those fed the bicarbonate diet on d 49 (2,671 vs. 2,484 g, respectively); however, other comparisons failed to reveal diet-related differences in heart weight, pulse oximetry values, electrocardiogram amplitudes, or blood-gas values (P > 0.05). When the data were resorted into categories based on right:total ventricular weight ratios (RV:TV) indicative of normal (RV:TV < 0.28) or elevated (RV:TV > or = 0.28) pulmonary arterial pressures, broilers with elevated RV:TV ratios had poorly oxygenated arterial blood that was more acidic, had high partial pressure of CO2 (PCO2), and had higher HCO3 concentrations when compared with broilers with normal RV:TV ratios. Experiment 2 was conducted to determine if metabolic variations associated with differences in feed intake or environmental temperature potentially could mask an impact of diet composition on blood-gas values. Male broilers maintained at thermoneutral temperature (24 degrees C) either received feed ad libitum or had the feed withdrawn > or = 12 h prior to blood sampling. Broilers fed ad libitum had lower venous saturation of hemoglobin with O2, higher venous PCO2, and higher arterial HCO3 concentrations than broilers subjected to feed withdrawal. Broilers in experiment 2 fed ad libitum and exposed to cool temperatures (16 degrees C) had lower arterial partial pressure of O2 and higher venous PCO2 than broilers fed ad libitum and maintained at 24 degrees C. Overall, these results demonstrate that changes in diet composition (control vs. 1% NaHCO3 diets) had minimal impact on arterial and venous blood-gas variables when compared with the more dramatic differences associated with feed intake (ad libitum vs. > or = 12 h withdrawal), environmental temperature (24 vs. 16 degrees C), and the pathogenesis associated with PHS (RV:TV < 0.28 vs. > or = 0.28).

Effect of cage vs. floor litter environments on the pulmonary hypertensive response to intravenous endotoxin and on blood-gas values in broilers

Intravenous endotoxin has been shown to trigger a delayed pulmonary hypertensive response that varies widely in magnitude and duration among individual broilers. It was proposed that this individual variability may reflect immunological differences acquired during previous respiratory challenges that might have subsequently altered the endotoxin-initiated biochemical cascade. In Experiment 1, we tested the hypothesis that, when compared with broilers reared in clean stainless steel cages (Cage group), broilers reared on floor litter (Floor group) should experience a greater respiratory challenge and therefore may consistently exhibit a more enhanced pulmonary hypertensive response to intravenous endotoxin. Birds in the Cage group were grown in stainless steel cages at a low density (72 birds/8 m2 chamber), and fecal and dander materials were removed daily. Birds in the Floor group were reared on wood-shavings litter at a higher density (110 birds/8 m2 chamber). Pulmonary and systemic mean arterial pressures and blood-gas values were evaluated prior to and following the intravenous administration of 1 mg Salmonella typhimurium endotoxin. Broilers in the Floor and Cage groups exhibited pulmonary hypertensive responses to endotoxin that were very similar in terms of time of onset, duration, and magnitude, as well as variability in the response among individuals. Systemic hypotension also developed similarly in both groups following endotoxin injection. Blood-gas values indicated that the partial pressure of CO2 and the HCO3- concentration in arterial blood were higher (P < 0.05) in the Floor group than in the Cage group prior to and subsequent to the endotoxin injection. In Experiment 2, we reevaluated the effect of a dirty vs. a clean environment on blood-gas values using a different strain of broilers, and confirmed the negative impact of floor rearing on blood-gas values. We conclude that broilers reared on the floor inhaled litter dust and noxious fumes, which impaired pulmonary gas exchange and increased the arterial partial pressure of CO2 when compared with broilers reared in clean stainless steel cages. Nevertheless, the pulmonary hypertensive response to endotoxin did not differ between broilers reared on the floor and those in cages.

Intravenous micro-particle injections and pulmonary hypertension in broiler chickens: acute post-injection mortality and ascites susceptibility

Intravenously injected micro-particles become trapped within the pulmonary vasculature where they increase the resistance to blood flow and trigger pulmonary hypertension. We tested the hypothesis that i.v. micro-particle injections can be used to trigger acute (24 to 48 h) post-injection mortality in broilers having the most limited pulmonary vascular capacity, or ascites in broilers whose marginal cardiopulmonary capacity renders them susceptible to pulmonary hypertension syndrome (PHS). Progressive inflammation-associated responses were initiated within the lung parenchyma by 10 to 80 microm diameter dextran polymer (Sephadex) and 30 microm diameter cellulose micro-particles, leading to the scavenging of Sephadex micro-particles from the pulmonary vasculature by <5 d post-injection, whereas the cellulose micro-particles persisted for >7 d post-injection. The persistency and size of the cellulose apparently facilitated chronic occlusion of blood flow through precapillary arterioles, thereby triggering appreciable post-injection mortality and PHS at relatively low injection volumes (0.3 to 0.6 mL at 0.02 g/mL). In contrast, the small size of the polystyrene microspheres (15 microm), and the lack of persistency of the Sephadex micro-particles, apparently precluded the reliable occurrence of post-injection mortality or PHS until higher volumes (>0.8 mL at 0.02 g/mL) were injected. Values for the total susceptibility index (TSI: 24 to 48 h post-injection mortality + PHS mortality) following cellulose injections were higher for broilers reared at cool temperatures than at thermoneutral temperatures. The incidences of PHS induced by exposing broilers from different genetic lines to constant cool temperatures qualitatively paralleled the respective post-injection mortalities elicited by injecting the cellulose micro-particle suspension into the same lines. These observations indicate the micro-particle injection methodology potentially can replace unilateral pulmonary artery occlusion as the technique of choice for genetically selecting broilers that have a sufficiently robust pulmonary vascular capacity to resist the onset of pulmonary hypertension and PHS. The functional importance of the relative antigenicity of different micro-particle types, and the extent to which key immune-mediated responses, either beneficial or detrimental, might be co-selected by the micro-particle injection technology, remain to be clarified.

Hyper- or hypothyroidism: its association with the development of ascites syndrome in fast-growing chickens

The ascites syndrome in broiler chickens is attributed to the progress in genetic selection for rapid growth, coupled with the metabolic burden imposed by exposure to a relatively low-ambient temperature (T(a)). The syndrome is mainly characterized by hematocrit elevation, decline in blood oxygen saturation, accumulation of fluid in the abdominal cavity, and finally, death. Ascitic chickens have demonstrated hypothyroidism coupled with a marked stress response (high corticosterone concentration) and reduction in the hemoglobin content. The objective of the present study was to examine the role of thyroid and corticosterone hormones in the development of the syndrome. Ascites was induced by exposure to a gradually declining T(a) and supplementation of a pellet-form diet. Exogenous thyroxin (T(4)) and propylthiouracil (PTU) (in Experiments 1 and 2, respectively) were supplemented in drinking water to induce hyper- or hypothyroidism, respectively. Ascites syndrome was developed in 21.5% and 23% of the birds exposed to ascites-induced conditions (Exps. 1 and 2, respectively). Excess T(4) (Exp. 1) significantly reduced the percentage of ascites (down to 7%), whereas PTU (Exp. 2) significantly increased the appearance of the syndrome (35%). In the T(4)-treated chickens, although the T(4) concentration reached pharmacological levels, the triiodothyronine (T(3)) concentration remained within physiological levels, whereas T(3) in the ascitic birds exhibited a reduction pattern similar to that observed in the ascitic non-supplemented ones. In the PTU-treated chickens, however, both ascitic and non-ascitic birds demonstrated significant reductions in both T(4) and T(3) concentrations. In both experiments, ascitic chickens exhibited a considerable stress response, characterized by a significant and persisted elevation in plasma corticosterone concentration, which was in accordance with a similar elevation of hematocrit, and the PTU-treated non-ascitic birds exhibited a similar stress response. At 5 weeks of age, ascitic birds and the PTU-treated non-ascitic ones exhibited significant reductions in the hemoglobin content of their red blood cells. It may be concluded that deficiency in the thyroid hormones and elevated corticosterone may play a key deleterious role in the development of the ascites syndrome.

Intravenous micro-particle injection and pulmonary hypertension in broiler chickens: cardio-pulmonary hemodynamic responses

Experiments were conducted to determine whether intravenous injections of micro-particles, having a size suitable to be trapped by the pulmonary precapillary arterioles, could be used to increase the pulmonary vascular resistance and thereby trigger an acute increase in the pulmonary arterial pressure (pulmonary hypertension). Anesthetized male broilers injected intravenously with inorganic (silica gel, polystyrene) or organic (cellulose, Sephadex) micro-particles developed an immediate pulmonary hypertension in proportion to the cumulative quantities of micro-particles injected. Micro-particle occlusion of a portion of the pulmonary arterioles forced the cardiac output to flow at a higher rate through the remaining vascular channels, thereby exposing a diffusion limitation characterized by undersaturation of the systemic arterial blood with oxygen (hypoxemia). The concurrent onset of systemic hypotension (reduced systemic arterial blood pressure) was not due to a reduction in cardiac output but rather was attributed to hypoxemic vasodilation of the systemic vasculature (reduced total peripheral resistance). Preliminary histological evaluations revealed micro-particles lodged in inter- and intraparabronchial arterioles, surrounded by aggregates of thrombocytes and mononuclear leukocytes within 30 min post-injection. These observations infer that intravenously injected micro-particles are carried to the lungs by the returning venous blood, where trapping of the micro-particles by the pulmonary vasculature triggers acute responses (increased pulmonary vascular resistance, pulmonary hypertension, systemic hypoxemia, systemic hypotension) that mirror those previously observed following acute occlusion of one pulmonary artery. Additional studies will be required to determine the extent to which the focal immune response to trapped micro-particles promotes local vasoconstriction that amplifies the pulmonary hypertension attributable to direct physical obstruction of precapillary arterioles.

Taurine, cardiopulmonary hemodynamics, and pulmonary hypertension syndrome in broilers

Previous studies have suggested cardiac taurine is released into the plasma in response to hypoxemia (low blood oxygen levels) during the pathogenesis of pulmonary hypertension syndrome (PHS, ascites). In the present study, broilers reared under cool temperature conditions (16 C) were provided tap water (control group), tap water supplemented with taurine, or tap water supplemented with the taurine transport antagonist beta-alanine. When compared with control values, taurine supplementation consistently elevated free taurine concentrations in the plasma but not in cardiac tissues, whereas beta-alanine supplementation consistently reduced free taurine concentrations in cardiac tissues but not in the plasma. Neither the incidence of PHS nor specific predictors of PHS susceptibility (electrocardiogram Lead II S-wave amplitude, % saturation of hemoglobin with oxygen, heart rate, right to total ventricular weight ratio) were affected by taurine or beta-alanine supplementation. Cardiopulmonary hemodynamic evaluations were conducted to compare control and beta-alanine supplemented broilers breathing room air or air containing 12% oxygen (low oxygen challenge). While breathing room air, the betaalanine-supplemented broilers had higher baseline values for cardiac output (186.2 vs. 146.9 mL/min/kg BW) and pulmonary arterial pressure (27.4 vs. 22.4 mm Hg), similar values for mean systemic arterial pressure (100 vs. 104 mm Hg) and pulmonary vascular resistance (0.062 vs. 0.064 resistance units), and lower values for total peripheral resistance (0.228 vs. 0.296 resistance units) when compared with control broilers breathing room air. During low oxygen challenges, the beta-alanine-supplemented broilers exhibited larger reductions in cardiac output, mean systemic arterial pressure, and pulmonary arterial pressure and greater increases in pulmonary vascular resistance than control broilers. These observations indicate that beta-alanine-supplemented broilers breathing room air had a higher systemic demand for oxygen as evidenced by their lower total peripheral resistance (systemic vasodilation) and had a capacity sufficient to pump a higher cardiac output and, thereby, maintain a similar mean systemic arterial pressure when compared with control broilers. However, cardiac function rapidly deteriorated in beta-alanine-supplemented broilers during low oxygen challenges, leading to substantially greater reductions in cardiac output, stroke volume, and mean systemic arterial pressure when compared with control broilers. Concurrent changes in pulmonary arterial pressure within the beta-alanine group reflect interactions between cardiac output and pulmonary vascular resistance. Overall, depleting cardiac taurine did not appear to initiate PHS, but systemic hypoxemia developing during the mid- to late-pathogenesis of PHS may expose and incipient cardiac weakness attributable to depleted taurine reserves.

Cardio-pulmonary function in preascitic (hypoxemic) or normal broilers inhaling ambient air or 100% oxygen

We evaluated the influence of the percentage saturation of hemoglobin with oxygen (HbO2) on the pulmonary arterial pressure in normal and preascitic (hypoxemic) broilers breathing ambient air or 100% O2. In Experiment 1, unanesthetized preascitic broilers (right:total ventricular weight ratios [RV:TV] = 0.32+/-0.02) breathing ambient air had initial values of 67% for HbO2 and 32 mm Hg for pulmonary arterial pressure. The HbO2 increased to > or =96.6% during inhalation of 100% O2; however, pulmonary arterial pressure was not reduced. In Experiment 2, anesthetized normal (RV:TV = 0.23; HbO2 = 88%) and preascitic broilers (RV:TV = 0.28; HbO2 = 76%) were compared. The groups did not differ in body weight or respiratory rate, but preascitic broilers had lower values for mean arterial pressure, total peripheral resistance, and partial pressure of O2 in arterial blood and had higher values for pulmonary arterial pressure. Inhaling 100% O2 increased HbO2 to 99.9% in both groups; however, pulmonary arterial pressure remained higher in preascitic than in normal broilers, and the pulmonary vascular resistance was not reduced during 100% O2 inhalation. Cardiac output was higher in preascitic than in normal broilers before and after, but not during, 100% O2 inhalation. Mean arterial pressure and total peripheral resistance increased in the preascitic but not in the normal group during 100% O2 inhalation. Low coefficients of determination (R2) were obtained for linear regression comparisons of HbO2 vs. pulmonary arterial pressure in both experiments. Overall, acute reversal of the systemic hypoxemia in preascitic broilers had little direct impact on pulmonary hypertension, providing no evidence of hypoxemic or hypoxic pulmonary vasoconstriction. Instead, acute reversal of the systemic hypoxemia primarily increased the total peripheral resistance and normalized the mean arterial pressure and cardiac output. A sustained reduction in cardiac output theoretically should attenuate pulmonary hypertension, but this was not observed because of the overriding influence of sustained pulmonary vascular resistance.