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

Co-infections of Enterococcus cecorum and various avian pathogens resulted in varying rates of SPF broilers with an E. cecorum infection

RESEARCH HIGHLIGHTS

Typical E. cecorum lesions can be reproduced in SPF broilers after intravenous, aerosol and oral inoculations.The respiratory route is potentially an infection route for pathogenic E. cecorum bacteria.Co-infections tested in this study or dexamethasone do not exacerbate the proportion of E. cecorum lesions.M.s. in combination with IBV or NDV vaccines exacerbates the proportion of positive reisolations.Immunosuppression induced by early CAV infection increases the proportion of positive reisolations.

SNP-based breeding for broiler resistance to ascites and evaluation of correlated production traits

Background

The goal of this study was to evaluate marker-assisted selection (MAS) in broiler chickens using previously mapped gene regions associated with ascites syndrome incidence. The second-generation MAS products were assessed for impact on ascites phenotype and whether there were associated changes in important production traits. Previously, we used whole genome resequencing (WGR) to fine-map 28 chromosomal regions as associated with ascites phenotype in our experimental ascites broiler line (Relaxed, REL) based on a hypobaric chamber challenge. Genotypes for single nucleotide polymorphisms (SNPs) in mapped regions on chromosomes 2 and 22, were used for MAS in our REL line. After two generations, birds homozygous for the genotypes associated with resistance for both chromosomal regions were established. The MAS F2 generation was then compared to the REL line for ascites susceptibility and 25 production traits.

Results

Selection based on SNPs in the carboxypeptidase Q (CPQ, Gga2) and leucine rich repeat transmembrane neuronal 4 (LRRTM4, Gga22) gene regions resulted in a sex- and simulated altitude- dependent reduction of ascites incidence in two F2 cohorts of the MAS line. Comparisons of the F2 MAS and REL lines for production traits when reared at ambient pressure found no significant negative impacts for feed intake (FI), feed conversion ratio (FCR), or deboned part yields for either sex for two F2 cohorts. There were, however, improvements in the MAS for full-trial body weight gain (BWG), FCR, absolute and relative tender weights, and relative drumstick weight.

Conclusions

These results validate the mapping of the 28 chromosomal regions and demonstrate that fine mapping by WGR is an effective strategy for addressing a complex trait; it also stands as the first successful SNP-based selection program against a complex disease trait, such as ascites. The MAS line is comparable and, in some instances, superior, in growth performance to the REL control while being more resistant to ascites. This study indicates that MAS based on WGR can provide significant breeding potential in agricultural systems.

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

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

Analysis of fluoroquinolones in dusts from intensive livestock farming and the co-occurrence of fluoroquinolone-resistant Escherichia coli

Fluoroquinolones are important therapeutics in human and veterinary medicine. This study aimed to retrospectively analyse sedimentation dusts from intensive-livestock-farming barns for fluoroquinolones and investigate the association between resistant Escherichia coli and the detected drugs. Sedimentation-dust samples (n = 125) collected (1980–2009) at 14 barns of unknown-treatment status were analysed by HPLC and tandem-mass spectroscopy to detect enrofloxacin, ciprofloxacin, marbofloxacin, and difloxacin. Recent microbiological data were included to investigate the relationship between fluoroquinolone presence and fluoroquinolone-resistant E. coli. Fifty-nine dust samples (47%) from seven barns contained fluoroquinolone residues. Up to three different fluoroquinolones were detected in pig and broiler barns. Fluoroquinolone concentrations ranged from 10-pg/mg to 46-ng/mg dust. Fluoroquinolone-resistant E. coli were isolated from four barns. Of all the dust samples, 22% contained non-susceptible isolates. Non-susceptible isolate presence in the dust was significantly associated (p = 0.0283) with detecting the drugs, while drug detection increased the odds (4-fold) of finding non-susceptible E. coli (odds ratio = 3.9877, 95% CI: 1.2854–12.3712). This retrospective study shows that fluoroquinolone usage leads to dust contamination. We conclude that farmers and animals inhale/swallow fluoroquinolones and fluoroquinolone-resistant bacteria due to drug application. Furthermore, uncontrolled drug emissions via air exhausted from the barns can be assumed.

Pilot study of long-term anaesthesia in broiler chickens

OBJECTIVE

To provide stable anaesthesia of long duration in broiler chickens in order to perform a terminal caecal ligated loop procedure.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Seven clinically healthy broiler chickens (Gallus domesticus) aged 27-36 days, weighing 884-2000 g.

METHODS

Anaesthesia was induced and maintained with isoflurane in oxygen. All birds underwent intermittent positive pressure ventilation for the duration. End-tidal carbon dioxide, peripheral haemoglobin oxygen saturation, heart rate and oesophageal temperature were monitored continuously. All birds received intraosseous fluids. Butorphanol (2 mg kg(-1)) was administered intramuscularly at two hourly intervals. Euthanasia by parenteral pentobarbitone was performed at the end of procedure.

RESULTS

Stable anaesthesia was maintained in four chickens for durations ranging from 435 to 510 minutes. One bird died and one was euthanized after 130 and 330 minutes, respectively, owing to surgical complications and another died from anaesthetic complication after 285 minutes.

CONCLUSIONS AND CLINICAL RELEVANCE

Long-term, stable anaesthesia is possible in clinically healthy chickens, provided complications such as hypothermia and hypoventilation are addressed and vital signs are carefully monitored. There are no known previous reports describing monitored, controlled anaesthesia of this duration in chickens.

Pharmacokinetic and pharmacodynamic properties of gamithromycin in turkey poults with respect to Ornithobacterium rhinotracheale

The macrolide gamithromycin (GAM) has the ability to accumulate in tissues of the respiratory tract. Consequently, GAM might be a suitable antibiotic to treat bacterial respiratory infections in poultry, such as Ornithobacterium rhinotracheale. As O. rhinotracheale infections are common in turkey flocks, the aim of this study was to determine the pharmacokinetic (PK) parameters of GAM in plasma, lung tissue, and pulmonary epithelial lining fluid (PELF) of turkeys and to correlate them with pharmacodynamic (PD) characteristics (PK/PD). The animal experiment was performed with 64 turkeys, which received either a subcutaneous (SC, n=32) or an oral (PO, n=32) bolus of 6 mg GAM/kg body weight (BW). GAM concentrations in plasma, lung tissue, and PELF were measured at different time points post administration (p.a.), and PK characteristics were determined using non-compartmental modeling. The maximum plasma concentration after PO administration was ten-fold lower than after SC injection (0.087 and 0.89 μg/mL, respectively), whereas there was no difference in lung concentrations between both routes of administration. However, lung concentrations at day 1 p.a. were significantly higher than plasma levels for both routes of administration (2.22 and 3.66 μg/g for PO and SC, respectively). Consequently, lung/plasma ratios were high, up to 50 and 80 after PO and SC administration, respectively. GAM could not be detected in PELF, although this might be attributed to the collection method of PELF in birds. The GAM minimum inhibitory concentration (MIC) was determined for 38 O. rhinotracheale strains; MIC50 and MIC90 were 2 and >32 μg/mL, respectively. PK/PD correlation for lung tissue demonstrated that the time above the MIC90 of the susceptible population (2 μg/mL) was 1 day after PO bolus and 3.5 days after SC administration. The area under the curve (AUClast)/MIC ratios for lung tissue after SC and PO administration were 233 and 90, respectively. To conclude, GAM is highly distributed to lung tissue in turkey poults, suggesting that it has the potential to be used to treat respiratory infections such as O. rhinotracheale.

Viral kinetics, shedding profile, and transmission of serotype 1 Marek's disease vaccine Rispens/CVI988 in maternal antibody-free chickens

Probably the most effective current vaccine against Marek's disease is the live Rispens (CVI988) attenuated serotype 1 Marek's disease virus (MDV). It is unknown whether the currently available Rispens vaccines transmit effectively between chickens. To investigate the kinetics and shedding of three commercially available strains of this virus and the extent of lateral transmission, we measured the shedding rate in dander and the viral load in peripheral blood lymphocytes (PBLs) and feather tips over time. Four identical climate-controlled rooms were stocked with a total of 70 specific-pathogen-free chickens for 56 days. In each of three rooms, 10 chickens were vaccinated with one of the commercial vaccines at day old and left in contact with 10 unvaccinated chickens. The fourth room contained 10 unvaccinated control chickens. As determined by MDV-specific quantitative real-time polymerase chain reaction of weekly room dust and individual PBLs and feather tip samples, the vaccine virus was shed from the vaccinated chickens in dander from day 7 postvaccination and transmitted effectively from vaccinated to in-contact chickens with a lag period of 2-3 wk. Viral load in PBLs and feather tips peaked at days 7 and 14, respectively, and declined thereafter, whereas viral load in dust increased rapidly to day 21 and then increased gradually thereafter. Antibody titer at day 56 was correlated with earlier measures of MDV load in PBLs but not feather tips or dust. These results show that currently available Rispens CVI988 vaccine virus is shed in significant quantities from vaccinated chickens and transmits effectively between chickens.

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.

A lack of antibody formation against inactivated influenza virus after aerosol vaccination in presence or absence of adjuvantia

In the poultry industry, infections with avian influenza virus (AIV) can result in significant economic losses. The risk and the size of an outbreak might be restricted by vaccination of poultry. A vaccine that would be used for rapid intervention during an outbreak should be safe to use, highly effective after a single administration and be suitable for mass application. A vaccine that could be applied by spray or aerosol would be suitable for mass application, but respiratory applied inactivated influenza is poorly immunogenic and needs to be adjuvanted. We chose aluminum OH, chitosan, cholera toxin B subunit (CT-B), and Stimune as adjuvant for an aerosolized vaccine with inactivated H9N2. Each adjuvant was tested in two doses. None of the adjuvanted vaccines induced AIV-specific antibodies after single vaccination, measured 1 and 3 weeks after vaccination by aerosol, in contrast to the intramuscularly applied vaccine. The aerosolized vaccine did enter the chickens' respiratory tract as CT-B-specific serum antibodies were detected after 1 week in chickens vaccinated with the CT-B-adjuvanted vaccine. Chickens showed no adverse effects after the aerosol vaccination based on weight gain and clinical signs. The failure to detect AIV-specific antibodies might be due to the concentration of the inactivated virus.

Plexiform lesions in the lungs of domestic fowl selected for susceptibility to pulmonary arterial hypertension: incidence and histology

Plexiform lesions develop in the pulmonary arteries of humans suffering from idiopathic pulmonary arterial hypertension (IPAH). Plexogenic arteriopathy rarely develops in existing animal models of IPAH. In this study, plexiform lesions developed in the lungs of rapidly growing meat-type chickens (broiler chickens) that had been genetically selected for susceptibility to IPAH. Plexiform lesions developed spontaneously in: 42% of females and 40% of males; 35% of right lungs, and 45% of left lungs; and, at 8, 12, 16, 20, 24, and 52 weeks of age the plexiform lesion incidences averaged 52%, 50%, 51%, 40%, 36%, and 22%, respectively. Plexiform lesions formed distal to branch points in muscular interparabronchial pulmonary arteries exhibiting intimal proliferation. Perivascular mononuclear cell infiltrates consistently surrounded the affected arteries. Proliferating intimal cells fully or partially occluded the arterial lumen adjacent to plexiform lesions. Broilers reared in clean stainless steel cages exhibited a 50% lesion incidence that did not differ from the 64% incidence in flock mates grown on dusty floor litter. Microparticles (30 μm diameter) were injected to determine if physical occlusion and focal inflammation within distal pulmonary arteries might initiate plexiform lesion development. Three months postinjection no plexiform lesions were observed in the vicinity of persisting microparticles. Broiler chickens selected for innate susceptibility to IPAH represent a new animal model for investigating the mechanisms responsible for spontaneous plexogenic arteriopathy.

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

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

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.

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.

The aetiology of hypoxaemia in chickens selected for rapid growth

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

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).

Role of the domestic chicken (Gallus gallus) in the epidemiology of urban visceral leishmaniasis in Brazil

Zoonotic visceral leishmaniasis (ZVL) is a serious public health problem in several Brazilian cities. Although the proximity of chicken houses is often cited as a risk factor in studies of urban ZVL, the role chickens play in the epidemiology of the disease has not been defined. Chickens attract both male and female sand flies (Lutzomyia longipalpis) but are unable to sustain Leishmania infections, and their presence may exert a zooprophylactic effect. We discuss environmental, physiologic, socioeconomic, and cultural factors related to chicken raising that could influence Le. infantum transmission in Brazilian cities and evaluate whether this practice significantly affects the risk of acquiring ZVL.

Ventilatory sensitivity to changes in inspired and arterial carbon dioxide partial pressures in the chicken

To determine if intrapulmonary chemoreceptors could be the sole peripheral chemoreceptors responsible for ventilatory responses to inhaled CO2, we studied the relationships of minute ventilation, tidal volume, and respiratory frequency to inspired and arterial partial pressure of CO2 (P(I)CO2 and PaCO2) in decerebrate upright chickens when the birds inspired gases containing four low partial pressures of CO2 (0.02, 5.0, 8.2, and 11.4 torr). Because of variability in the measured variables from time to time in the same birds, as well as between birds, and because of the limited precision in measuring PaCO2, a 4 x 4 Latin square design and four statistical methods of data analyses (modified reduced major axis estimator, maximum likelihood estimator, average slope method, and summary slope method) were used. Tidal volume, minute ventilation, and PaCO2 increased, but respiratory frequency remained unchanged, as gases containing increased partial pressures of CO2 were inhaled. The results indicate that intrapulmonary chemoreceptors are not the sole receptors stimulated by inhaling gas containing even low partial pressures of CO2 and that stimulation of arterial and central chemoreceptors also occurs. Stimulation of these latter chemoreceptors may account for the increase in ventilation. Further, the results demonstrate the importance of maintaining a low level of environmental CO2 in poultry houses to minimize its influence on ventilation.

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.

Pulmonary hypertension syndrome in broilers caused by Enterococcus faecalis

A field strain of Enterococcus faecalis was administered to broiler chicks at doses of 0, 3 x 10(6), 1.5 x 10(7), and 2 x 10(7) bacteria/bird either intra-abdominally or intravenously. In trials 1 to 3, birds were reared communally in a broiler house on pine shaving litter. In trial 4, challenged and control birds were maintained in separate isolation rooms in metal cages with raised wire floors. Challenged birds exhibited a characteristic cavity or depression in the external wall of the right ventricle. A subjective scoring system was devised to quantify challenge effects by assigning each heart a score of 1 to 4. The average number of birds, over all trials and over all dose levels, exhibiting the ventricular cavity was 93%. This value in controls was 5%. The average heart score for challenged birds was 3.1, and that for controls was 0.20. Heart scores of challenged and control chicks were not different in birds reared communally or in separate isolation rooms. Additionally, both routes of administration were equally effective. Results suggest that challenge with E. faecalis caused pulmonary hypertension.

The effect of dietary chloride and bicarbonate on blood pH, haematological variables, pulmonary hypertension and ascites in broiler chickens

1. The effect of supplementing grower diets with bicarbonate or chloride on haematological variables, pulmonary hypertension syndrome and ascites in broilers exposed to cold temperature was investigated. 2. High concentrations of dietary chloride had no effect on the pH of the venous blood but a low chloride/high bicarbonate diet significantly increased blood pH. There was no consistent effect of dietary chloride or bicarbonate concentrations on growth performance, although in 1 experiment birds given a low chloride/high bicarbonate diet consumed less food and gained less weight than controls. 3. Birds fed on high-chloride diets tended to have a higher incidence of ascites and pulmonary hypertension than controls. Birds fed on low-chloride and high-bicarbonate diets had significantly lower pulmonary hypertension and lower heart weights, which may have indicated a decrease in pulmonary and systemic blood pressure. 4. We conclude that increasing dietary bicarbonate and reducing dietary chloride has potential as a low cost and effective method to reduce the pulmonary hypertension which leads to ascites in broiler chickens.

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.

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.

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.

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

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