Phenotypic and genotypic characterization of Salmonella arizonae from an integrated turkey operation.

Fifty cases submitted between 2000 and 2002 were selected for retrospective analysis to evaluate possible relationships between Salmonella arizonae isolated from breeder flocks, hatching eggs, and meat bird flocks belonging to a single turkey integrator. In all the meat bird cases selected for this study, arizonosis was the primary diagnosis. In birds under 1 month of age, clinical signs and pathologic changes were observed in older birds. The Salmonella arizonae isolates were analyzed by antibiotic resistance pattern and serotype and genotyped by pulsed-field gel electrophoresis (PFGE). Serotyping and PFGE yielded similar results, but the antibiotic resistance patterns did not correspond to either serotyping or PFGE typing. The presence of common pulsed-field patterns in breeder flocks, eggs, and meat bird flocks suggested that S. arizonae was being transmitted vertically from the breeder flock.

In vitro hypoxia differentially affects constriction and relaxation responses of isolated pulmonary arteries from broiler and leghorn chickens.

Under normoxic conditions in vitro, isolated pulmonary arteries from broilers exhibit reduced endothelium-dependent relaxation responses when compared with Leghorns. In vivo, hypoxia increases the susceptibility of broiler chickens to pulmonary hypertension syndrome (PHS), whereas Leghorns are considered resistant to PHS. Because L-arginine supplementation decreases the incidence of PHS in vivo and improves the relaxation responses of broiler isolated pulmonary arteries in vitro, we hypothesized that in vitro hypoxia would further reduce the relaxation responses of broilers to endothelium-derived nitric oxide (EDNO)-dependent vasodilators and that L-arginine supplementation would alleviate this impairment. As a test of this hypothesis, pulmonary arteries from broiler and Leghorn chickens were isolated and exposed to normoxia or hypoxia in the presence or absence of L-arginine while their constriction and relaxation responses to vasoactive compounds were recorded. In broilers, hypoxia did not affect the constriction responses of isolated pulmonary arteries but decreased EDNO-dependent acetylcholine-induced relaxation responses. In contrast, in Leghorns hypoxia increased endothelin-1-induced vasoconstriction responses and reduced the EDNO-dependent relaxation responses only to the lowest concentration of acetylcholine used. L-Arginine supplementation augmented the relaxation responses to acetylcholine in broilers and Leghorns under normoxia but failed to augment them under hypoxia. Relaxation responses to the NO donor, sodium nitroprusside, were not affected by hypoxia in Leghorns but were increased by hypoxia in broilers. These results suggest that the increased incidence of PHS in broiler chickens reared under hypoxia may be associated with a hypoxia-induced reduction in the synthesis or activity of EDNO in the pulmonary circulation.

Prevalence of pathogenic Escherichia coli in the broiler house environment.

Matched sampling of Escherichia coli from broiler house litter and bird lesions of either cellulitis or colibacillosis was conducted to investigate the relationship of pathogenic E. coli to those found in the environment. Isolates were collected from six broiler flocks representing six geographically disparate ranches. Isolates were compared by flock for similarity in serotype and genotyped by pulsed-field gel electrophoresis. Serotyping revealed a considerable dissociation between the two groups of isolates. The prevalence of pathogenic E. coli that matched the environmental isolates from the same house was 0 to 3%. Statistical analysis of the serotype data showed a strong dependence of serotype on isolate source, indicating a high probability that a particular serotype would be found among lesions or litter but not in both groups. Genotyping of isolates on two farms supported the results of serotyping and provided differentiation of isolates that could not by typed by serology. These results suggested that the prevalence of pathogenic E. coli in the broiler house was independent of the prevalence of other commensal or environmental E. coli. Understanding the composition of E. coli populations in commercial poultry production may have bearing on the epidemiology and control of E. coli related diseases.

Virulence factors of Escherichia cofi from cellulitis or colisepticemia lesions in chickens.

This study was designed to compare virulence factors of cellulitis-derived Escherichia coli to colisepticemic E. coli in order to clarify whether E. coli associated with cellulitis comprise a unique subset of pathogenic E. coli. Isolates were tested for serotype, capsule, aerobactin production, colicin production, the presence of the iss gene, and serum resistance. Untypable isolates made up the greatest percentage of each group. Serotypes O2 and O78 were the most commonly identified among both groups of isolates. No statistical differences in the distribution of aerobactin or colicin production, capsule, or iss gene were observed between groups. Cluster analysis showed that 90% of the E. coli isolates had greater than 42% livability in serum-resistance tests. No separation of colisepticemic vs. cellulitis E. coli isolates was observed on the basis of SR. Colicin production by E. coli was highly correlated with serum resistance (P = 0.0029). These data suggest that cellulitis E. coli have virulence traits similar to those of colisepticemic E. coli.

Prevalence of campylobacter spp. from skin, crop, and intestine of commercial broiler chicken carcasses at processing.

This study describes the prevalence of positive Campylobacter cultures from the skin, crop, and intestine of postscald broiler chicken carcasses at processing. Six to 12 carcasses from 22 flocks were sampled. Skin was cultured by direct plating of a cotton swab, whereas crop and intestine were cultured from tissue that was aseptically harvested and stomached in PBS before plating. Cultures were not enriched prior to plating. The methods used in this report are compared to those used by others. In this study, skin samples were 78% positive; crops were 48% positive, and intestines were 94% positive (n = 202). Based on our results, if the intestine was positive for Campylobacter, the odds of finding a positive crop culture was 8.6 times greater, and the odds of finding a positive skin culture was 35 times greater than if the intestinal culture was negative for Campylobacter. These data suggest that the intestine was the most likely organ of those tested to be positive in postscald broiler carcasses from positive flocks. Further, if only one organ can be sampled, intestinal samples are most likely to reflect the prevalence of Campylobacter in a flock.

Selection bias in epidemiological studies of infectious disease using Escherichia coli and avian cellulitis as an example.

In epidemiological studies of infectious disease, researchers often rely on specific cues of the host, such as clinical signs, as surrogate indicators of pathogen presence. A selection bias would manifest if the specific visual cues used in sampling for the pathogen were not representative of the full range of signs caused by the strains of that pathogen. In our molecular epidemiological studies of Escherichia coli associated with avian cellulitis in broilers, we collect carcasses at the processing plant based on visual cues of lesion morphology. Therefore, the objectives of this study were to: (1) explore the potential impacts of selection bias in an application of infectious disease epidemiology, and (2) utilize a validation protocol to assess the potential for selection bias in our molecular epidemiological studies of E. coli and avian cellulitis. In two different trials, E. coli DNA fingerprints were compared between birds that our observers collected and the birds that the observers missed. Using Fisher's exact tests and simulation models, we determined that the isolates collected by the observers were not significantly different from the isolates missed by the observers (P > 0.60 in both trials). Our method of selecting birds suspected of having cellulitis did not significantly bias our inferences about the population of E. coli associated with cellulitis in the flock. We encourage more investigators to critically assess the relationship of the sample to the target population in epidemiological studies of infectious disease.

Prevalence of Campylobacter and Salmonella at a squab (young pigeon) processing plant.

Microbiological testing for Campylobacter and Salmonella was performed at a processing plant for squab (young pigeon) in three separate trials. Live birds, carcasses, and equipment were targeted for sampling during the preslaughter, pre-evisceration, and postevisceration stages of processing. The three trials represented 18 farms (1,110 squab), 1 farm (250 squab), and 23 farms (2,900 squab). The overall prevalence of positive samples in Trial 1 was 1.4% for Salmonella spp. and 11.1% for C. jejuni; in Trial 2, 4.3 and 0% for Salmonella spp. and C. jejuni; and in Trial 3, 4.1 and 4.8% for Salmonella spp. and C. jejuni, respectively. These observations represent a significantly greater likelihood of having a positive sample for Campylobacter (twofold) or Salmonella (eightfold) at processing, compared with prevalences observed in our previous on-farm study. This finding suggests an overall increase in the number of carcasses contaminated or in the concentration of contamination during transport and processing. In the multifarm trials, only Trial 3 demonstrated a significant increase in the prevalence of positive samples from the preslaughter to the postevisceration stages of processing (P = 0.02), and only for Campylobacter. The prevalence of positive cultures from equipment surfaces were not different than carcasses during processing, therefore no additional critical control points were identified within this system. When pooled swabs were compared (Trial 1) to individual swabs (Trials 2 and 3), no statistical difference in the prevalence of Salmonella or Campylobacter was observed between trials. Direct plating from a pooled sample onto selective agar media (Trial 1) and single swab culture with enrichment followed by plating on selective agar (Trials 2 and 3) were compared for Campylobacter isolation. No statistical difference in C. jejuni prevalence was observed using either method; however, when the detection limit of each method was determined, single swabs with enrichment had greater sensitivity.

Farm and management variables linked to fecal shedding of Campylobacter and Salmonella in commercial squab production.

A cross-sectional study was performed to determine the relationship of farm variables and management practices to fecal shedding of Campylobacter or Salmonella on commercial squab (young pigeon) farms. A detailed survey provided information on biosecurity, cleaning and disinfection, bird health, vector control, and loft and pen. Twenty pigeons on each of 12 farms were cultured before and after the producers completed a voluntary quality assurance training program (QAP), based on principles of hazard analysis critical control point (HACCP). The prevalence of positive samples for Salmonella and C. jejuni was 1/480 (0.21%) and 19/480 (3.96%), respectively. Campylobacter was present on one farm during both visits; three farms during the first visit, and three farms during the second visit. Analysis by fixed-effects logistic regression showed the probability of having a positive C. jejuni culture was increased by not using dry manure in the nesting material, not cleaning shipping crates, cleaning landing boards, and by increased frequency of chemical disinfection of water. Having a positive parent and higher numbers of squab per pen (density) were also associated with higher odds of being positive for C. jejuni. Factors not associated with a positive C. jejuni culture included, other avian species on the farm, type of shipping crate, covered drinkers, fly problems, bird age, level of nest box within the loft, and QAP training. Prevalence of food safety pathogens was extremely low on the squab facilities tested as compared with reports from commercial broiler or turkey flocks. This observation suggests that one or more farm variables or management practices were effectively reducing infection, or possibly a species-related difference existed in carriage rates and shedding of pathogens. These results emphasize critical control points for food safety pathogens may vary widely, and the formulation of effective QAP programs are dependent on science-based knowledge of diverse animal production systems.

The probability of severe disease in zoonotic and commensal infections.

Cross-species transfers of pathogens (zoonoses) cause some of the most virulent diseases, including anthrax, hantavirus and Q fever. Zoonotic infections occur when a pathogen moves from its reservoir host species into a secondary host species. Similarly, commensal infections often have a primary reservoir location within their hosts' bodies from which they rarely cause disease symptoms, but commensals such as Neisseria meningitidis cause severe disease when they cross into a different body compartment from their normal location. Both zoonotic and commensal infections cause either mild symptoms or severe disease, but rarely intermediate symptoms. We develop a mathematical model for studying three factors that affect the probability of severe disease: the size of the inoculum, the route of inoculation and the frequency of naturally occurring infections that do not cause symptoms but do induce protective immunity (vaccinating inoculations). With a single route of infection, increasing pathogen density causes inoculations to develop more often into disease rather than asymptomatic vaccinations that provide protective immunity. With two routes of infection, it may happen that a lower density of a pathogen or of a particular antigenic variant leads to a relatively higher frequency of disease-inducing versus vaccinating inoculations. This reversal occurs when one route of infection tends to vaccinate against relatively common pathogens but less often vaccinates against relatively rare pathogens, whereas the other route of infection is susceptible to disease-inducing inoculation even at relatively low pathogen density.

Persistence of cellulitis-associated Escherichia coli DNA fingerprints in successive broiler chicken flocks.

Avian cellulitis in broiler chickens is primarily caused by Escherichia coli. Previous research found that the E. coli isolates of cellulitis origin were unique to each ranch, suggesting that these E. coli were endemic within the ranch environment. To test the hypothesis that the E. coli associated with cellulitis are endemic in the litter of the broiler house, we designed a study to determine whether E. coli DNA fingerprints associated with cellulitis persist over successive flocks that are grown in the same house. In addition, we assessed the impact of different cleaning and disinfection strategies on this persistence. Two broiler houses were followed on each of five farms over 3-4 flocks. A total of 353 E. coli isolates from cellulitis lesions were analyzed in this study, and 314 of these isolates (89%) were DNA fingerprinted by PFGE. In each ranch, there were several DNA fingerprint patterns that were present over successive flocks, regardless of the cleaning and disinfection strategy utilized. Isolates persisted as long as 191 days, implying that these E. coli are capable of persisting in the broiler house environment for long periods of time. In addition, these E. coli isolates were associated with cellulitis lesions in successive flocks. Thus, the isolates of E. coli that are associated with cellulitis in broiler chickens appear to be endemic in the litter environment of the broiler house.

A field-suitable, semisolid aerobic enrichment medium for isolation of Campylobacter jejuni in small numbers.

The objective of this study was to produce an economical, easy to prepare, field-suitable enrichment medium for detection of Campylobacter jejuni in small numbers. A semisolid aerobic enrichment medium was developed. Rates of recovery from inoculated medium, sterile swabs, and mixed cultures of C. jejuni and coliform bacteria were tested.

A statistical model for assessing sample size for bacterial colony selection: a case study of Escherichia coli and avian cellulitis.

A general problem for microbiologists is determining the number of phenotypically similar colonies growing on an agar plate that must be analyzed in order to be confident of identifying all of the different strains present in the sample. If a specified number of colonies is picked from a plate on which the number of unique strains of bacteria is unknown, assigning a probability of correctly identifying all of the strains present on the plate is not a simple task. With Escherichia coli of avian cellulitis origin as a case study, a statistical model was designed that would delineate sample sizes for efficient and consistent identification of all the strains of phenotypically similar bacteria in a clinical sample. This model enables the microbiologist to calculate the probability that all of the strains contained within the sample are correctly identified and to generate probability-based sample sizes for colony identification. The probability of cellulitis lesions containing a single strain of E. coli was 95.4%. If one E. coli strain is observed out of three colonies randomly selected from a future agar plate, the probability is 98.8% that only one strain is on the plate. These results are specific for this cellulitis E. coli scenario. For systems in which the number of bacterial strains per sample is variable, this model provides a quantitative means by which sample sizes can be determined.

Echocardiographic study of pulmonary hypertension syndrome in broiler chickens.

Echocardiography was used to study cardiovascular structure and function during the development of pulmonary hypertension syndrome (PHS) in broiler chickens. Body weight-normalized right and left ventricular diameters at both end-diastole (RVDD, LVDD) and end-systole (RVDS, LVDS) were determined weekly in broilers reared under either normobaric (altitude, 96.7 m) or hypobaric conditions (simulated altitude, 2900 m) until 5 wk of age. Hypobaric-exposed broilers had larger RVDD at 3 and 4 wk of age and larger RVDS at 3, 4, and 5 wk of age. Hypobaric-exposed broilers also had larger LVDD at 2, 3, 4, and 5 wk of age and larger LVDS at 4 wk of age. Right (RVFS) and left ventricular fractional shortening (LVFS) were smaller in hypobaric- vs. normobaric-exposed broilers at 3, 4, and 5 wk of age and at 4 wk of age, respectively. Among hypobaric-exposed birds, PHS-positive (+) broilers had larger RVDD and RVDS than PHS-negative (-) broilers on week 3 and on weeks 1 and 3 after hypobaric exposure, respectively. PHS-positive (+) broilers also had smaller RVFS on week 1 after hypobaric exposure. Electrocardiographic and post-mortem data indicated that PHS+ broilers also developed right ventricular hypertrophy when compared with PHS-negative (-) broilers. These results are consistent with the hypothesis that PHS develops as a result of pulmonary hypertension and cardiac overload and suggest that PHS+ broilers have a greater and more persistent reaction to hypoxia than PHS- broilers.

Spatial heterogeneity of Escherichia coli DNA fingerprints isolated from cellulitis lesions in chickens.

Avian cellulitis in broiler chickens is characterized by subcutaneous lesions that result in economic losses because of the partial or complete condemnation of the carcasses at processing. Escherichia coli is the primary causative agent of this condition. Previous research with a biotyping system found that the E. coli of cellulitis origin were unique to each ranch, suggesting that these E. coli were endemic within the ranch environment. The objective of our study was to analyze the genetic variability of E. coli isolates associated with cellulitis. We analyzed the genetic relatedness of the isolates in relation to the houses, ranches, and complexes in which the broilers were grown. This analysis enabled us to assess the spatial heterogeneity, or genetic diversity on a spatial scale, of the isolates. Forty-nine broilers with cellulitis lesions were necropsied. These broilers came from six houses on four ranches on three complexes that had been placed with chicks from the same hatchery within a 2-wk period. Isolates of E. coli from the lesions were DNA fingerprinted by pulsed-field gel electrophoresis. Relatedness among isolates was determined with the Dice coefficient and an unweighted pair group method with average linkages cluster analysis. The complexes possessed isolates with a variety of DNA fingerprints, yet each complex appeared to have isolates with a unique set of DNA fingerprints. Isolates from the same complex tended to form clusters with similarity coefficients greater than 90%. Isolates from different complexes were genetically distinct. This heterogeneity at the level of the complex suggests that isolates were not disseminated from a source common to the complexes. The spatial heterogeneity of the E. coli isolates in this study implies an endemic population of cellulitis-associated E. coli exists in the broiler house environment.

Application of phonocardiography for detecting hypoxia-induced cardiovascular adaptation in the chicken.

Phonocardiography was evaluated as a noninvasive technique for diagnosis of cardiovascular adaptation and disease in broiler chickens. Heart sounds (HSs) were compared in a fast-growing (FG) commercial broiler line that is highly susceptible to chronic right heart failure resulting from pulmonary hypertension syndrome (PHS) and in a non-selected slow-growing (SG) broiler line that is resistant to PHS. HSs were analyzed in broilers reared in hypobaric hypoxia (HYP) and normobaric (CON) conditions. PHS was induced by a combination of embryonic hypoxia and HYP exposure. HSs were recorded with a microphone placed at the thoracic inlet of each chicken. Electrocardiograms were used to mark the sampling interval for the first, second, and total HS. Digitized HS signals were analyzed for peak frequency, mean peak frequency, and band width. Birds were examined for PHS lesions when 6 wk of age, at the end of each experiment. HSs were compared by line and treatment (Experiment 1) or by treatment and week (Experiment 2). In addition, HS frequencies were analyzed within the HYP treatment group for differences between birds with severe or no gross PHS lesions. HS frequencies generally decreased with age and were also lower in the FG than the SG line. Hypobaric exposure decreased all HS frequencies in the SG line and components of the first HSs in the FG line. The SG line did not develop gross lesions of PHS. In the FG line, significant differences in HS frequencies were observed between HYP and CON groups but not between PHS- and PHS+ broilers. Frequency changes described in humans with PHS were not observed. Further development to maximize the resolution of the HS waveforms and improved matching of the sampling interval to the electrical or hemodynamic output of the chicken heart may allow its use as a diagnostic tool for differentiating broilers with normal cardiac function or physiologic adaptation from those with cardiovascular disease.

Assessing cellulitis pathogenicity of Escherichia coli isolates in broiler chickens assessed by an in vivo inoculation model.

The purpose of this study was to identify Escherichia coli isolates that could be characterized as cellulitis pathogens. Twelve E. coli isolates from diagnostic cases of cellulitis or mixed infections with various serotypes were compared for ability to produce cellulitis and internal lesions indicative of systemic infection. Ranking of isolates was based on the premise that E. coli isolates that were "cellulitis-type" would cause cellulitis lesions without causing systemic infection. A quantitative scoring system was also used so both the time required for a lesion to develop and lesion severity could be evaluated as determinants of virulence. Escherichia coli isolates were inoculated by subcutaneous injection of a standardized dose in 24 broiler chickens per isolate. Necropsy was performed on four birds per group at 6, 12, 24, 36, 48, and 60 hr postinoculation (PI). Cellulitis lesions were scored on a 0 to 5 scale based on size, migration from the inoculation site, and gross characteristics. Lesions of the pericardium, liver, joint, or body cavity were evaluated. Gross lesion scores of 1 or 2 were evident by 6 hr PI with all isolates. Mortality occurred in 4 of 12 experimental groups. Internal lesions were observed in 3 to 12 birds per group. Escherichia coli was reisolated from all lesions. The four isolates with the highest lesion score and highest lesion points as determined by the quantitative scoring system did not vary. However, the rankings of two other isolates were affected. Four isolates that were below average for mean internal lesion score and above average for mean cellulitis points were characterized as cellulitis-type. Three isolates that were above average for internal lesion score and below average for mean cellulitis points were characterized as systemic-type. The E. coli serotype was not a determining factor for cellulitis-type pathogenicity. Isolates discriminated as cellulitis-type or septicemic-type E. coli in this study are being used to further investigate virulence factors involved in the pathogenesis of cellulitis in broiler chickens.

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

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

Echocardiographic evaluation of cardiac structure and function in broiler and Leghorn chickens.

This study was conducted to validate echocardiography in chickens, and to compare cardiac structure and function between broiler and Leghorn chickens. Diameters of the right and left ventricles, and thicknesses of the left ventricular free wall and the interventricular septum were measured echocardiographically in 5- and 7-wk-old chickens from both lines. Images were obtained from minimally restrained, standing birds using a 7.5 MHz probe placed in a parasternal position. End-systolic and end-diastolic echocardiographic measurements were compared with post-mortem measurements of the same variables. Comparisons resulted in correlation coefficients greater than 0.70 between in vivo (echocardiographic) and post-mortem measurements of the same variables, with post-mortem measurements more closely resembling end-diastolic echocardiographic measurements. After being normalized to body weight, post-mortem myocardial thicknesses, aortic and left ventricular diameters, heart weight at 5 wk of age, and left ventricular weight at 7 wk of age were smaller in broiler than in Leghorn chickens. Echocardiographic parameters, including ventricular wall thicknesses, ventricular diameters, and left ventricular fractional shortening, were also smaller in the broiler chicken. Right ventricular fractional shortening did not differ between the chicken lines. These results indicate that echocardiography is a useful noninvasive technique for in vivo evaluation of cardiac structure and function in the chicken, and that broiler chickens have a relatively smaller structural and functional heart than Leghorn chickens.

Research notes: Prevalence of selected microbial pathogens in processed poultry waste used as dairy cattle feed.

Processed poultry litter intended for dairy cattle feed was collected on 13 dairy ranches in the San Joaquin Valley of California and analyzed for the presence of significant bacterial pathogens associated with clinical disease in cattle or foodborne disease in humans. Litter samples were collected from the surface and interior of the litter piles upon arrival on the dairies and 2 to 4 wk later. Litter samples were cultured for Salmonella, Escherichia coli, Campylobacter, and other bacteria. The temperature of the litter piles was obtained on the surface and interior at each sampling. Dry matter was determined for each sample. No Salmonella, E. coli O157, or Campylobacter was identified (n = 104). Other E. coli strains were found in 8 out of 52 samples on arrival and 4 out of 52 samples at 2 to 4 wk after arrival. Although the surface and interior temperatures of the litter pile were different (23 C vs 50 C, respectively), the mean temperatures did not significantly change with time on the ranches. Average dry matter content did not differ between samples. In conclusion, the pathogens under investigation were not detected in processed poultry litter on these California dairy ranches upon arrival at the dairy or 2 to 4 wk later.

Experimental reduction of eggshell conductance during incubation. I. effect on the susceptibility to ascites syndrome.

Two hundred-four fertile broiler chicken eggs were obtained from a commercial source and divided into three equal groups. On day 1 of incubation, 68 eggs were selected randomly and four strips of vinyl tape were applied to the shell below the air cell (tape-day 1) to reduce eggshell conductance. This procedure was repeated with an additional group of 68 eggs on day 14 (tape-day 14). Sixty-eight eggs were incubated without treatment, as controls. One week after hatch, 20 chickens from each treatment group and control group were placed into a hypobaric chamber (simulated altitude of 2500 m) for 5 weeks. The remaining chickens in each group were maintained under normobaric conditions. The hematocrit and the mean frontal resultant electrical vector (MRV) of the heart were measured following 1 week, 3 weeks, and 5 weeks of hypobaric or normobaric exposure. Surviving chickens were euthanized at the end of 5 weeks. The weight ratio of right ventricle to left ventricle plus septum (the hypertrophy index [HI]) and the cardiac index, the HI divided by body weight, were determined. All mortality during the study was subjectively scored for the presence of ascites syndrome lesions. The percentage of chickens dying during, or exhibiting ascites syndrome at the completion of, the 5-week hypobaric exposure was 16.7%, 66.7%, and 58% for control, tape-day 1, and tape-day 14 treatments, respectively. MRV values of birds following hypobaric exposure were significantly different between treatment and control groups of the hypobaric exposure and between the two tape treatments. These results suggest that reducing conductance of the eggshell during incubation significantly potentiates the development of ascites syndrome in the broiler chicken.