Factors affecting the development of respiratory disease complex in chickens

Factors playing a part in the development of respiratory disease complex in chickens were investigated in a series of experiments. The experimental infection was produced by exposing chickens to Mycoplasma gallisepticum and the B1 vaccine strain of Newcastle disease virus and later exposing them to aerosols containing the O1:K1 serotype of Escherichia coli. Chickens became susceptible (pericarditis or death) to E. coli 8 days after mixed respiratory disease challenge. One day after respiratory disease challenge, lesions consisted of edema and infiltration with lymphoid cells and heterophils. At the time of susceptibility to E. coli, the lesions were strongly lymphoid with many dense follicular areas and very few heterophils. The incidence of pericarditis and death was similar when the concentration of bacteria in the aerosol inoculum ranged between 10(9)/ml and 10(5)/ml. At the time of maximum susceptibility to aerosol challenge, chickens were less susceptible to intravenously administered E. coli than were the uninfected controls. Resistance of chickens that had been selectively bred for a high (HA) or low (LA) antibody response to sheep erythrocytes was compared. HA chickens were more resistant to respiratory agents and less resistant to E. coli than LA line chickens. When the lines were exposed to respiratory disease followed by exposure to aerosols containing E. coli, the HA line had the lowest incidence of pericarditis and death.     

Response to Eimeria tenella of chickens selected for high or low antibody response and differing in haplotypes at the major histocompatibility complex.

Sublines of chickens selected for high antibody (HA) or low antibody (LA) response that differed at the major histocompatibility complex (MHC) were tested for response to Eimeria tenella. In Expt. 1, the first exposure to E. tenella was natural (in floor pens), and chicks were challenged orally 21 days later with 0, 928, or 1855 oocysts. In Expt. 2, chicks were reared in wire-floored batteries, vaccinated orally with 928 oocysts, and challenged orally 12 days later with 15,844 oocysts. Corticosterone (20 mg/kg) was mixed with feed from 24 hr before vaccination to 120 hr after vaccination in Expt. 2. In Expt. 1, LA chicks had more-severe cecal lesions but gained relatively more body weight after challenge than did HA chicks. In Expt. 2, cecal lesions were least severe in HA chicks that had been fed corticosterone, most severe in LA chicks fed corticosterone, and intermediate in chicks that were not fed corticosterone. No differences in response to E. tenella occurred as a result of haplotypes at the MHC.     

Genetic-environmental interactions and antibody response in chickens to two antigens

Chickens from lines selected for either a high (HA) or low (LA) antibody response to sheep erythrocytes were either socialized, ignored, or stressed before being injected with two different erythrocyte antigens. Correlation between the antibody responses to the two antigens and the difference between the titers of the HA and LA lines was greatest when the chickens were socialized in an optimum-stress environment. The antibody responses of individual chickens to the two antigens was influenced by their heterophil/lymphocyte ratios.     

Quantitative measures of disease in broiler breeder chicks of different major histocompatibility complex genotypes after challenge with infectious bursal disease virus

Criteria for evaluating genetic differences in resistance and susceptibility to infectious bursal disease (IBD) within a commercial broiler breeder line of chickens were compared. Line A broiler breeder chickens were challenged with graded doses of Animal and Plant Health Inspection Service (APHIS) strain IBD virus (IBDV) and evaluated at 2 time points, 3 days postinoculation (PI) and 10 days PI. Measures obtained at both time points included bursa to body weight, bursa histology, bursa lymphocyte count, and percentage of T cells in the bursa. Furthermore, viral load in the bursa was determined 3 days PI and anti-IBDV antibody titers, 10 days PI. A dose of 50 50% embryo infective dose caused IBD in about half the line A birds at the 10-day time point, and this dose was chosen for further studies. The data were analyzed for correlation among the various measures. Comparison of the 3-day- and 10-day-PI bursa lymphocyte counts indicated that birds challenged with low doses of virus suffered lymphocyte depletion at the 3-day time point, but many or all (depending on the dose) recovered by the 10-day time point. With a viral dose that caused bursal atrophy in about half the birds by 10 days PI, families segregating for 2 major histocompatibility complex (MHC) haplotypes were compared in terms of resistance to IBD. Results indicated that there was no difference among the 3 MHC genotypes in incidence of IBD by any of the disease measures.     

Immunological parameters in meat-type chicken lines divergently selected by antibody response to Escherichia coli vaccination.

Our group has established two lines of meat-type chickens divergently selected for early (HC line) and late (LC line) antibody responsiveness at 10 days of age to immunization with inactivated pathogenic Escherichia coli bacteria. The question addressed in the study presented here is whether this selection has changed other immunological responses, increasing the overall 'early' immunocompetence. Broilers of the third and fourth generations (S3 and S4) of the selected lines (HC and LC) and a control, unselected line (CT) were vaccinated at 10 days of age with E. coli vaccine, Newcastle virus vaccine (NDV), sheep erythrocytes (SRBC) or bovine serum albumin (BSA). Line-HC chicks exhibited higher antibody titers to E. coli, NDV and SRBC than CT or LC chicks. At 20 days of age HC chicks demonstrated a higher total protein and a higher beta- and gamma-globulin levels in their serum. At 21 days of age, HC chicks cleared carbon particles faster than LC chicks. Peripheral blood lymphocytes (PBL) from HC chicks vaccinated with E. coli vaccine, proliferated in vitro more actively in the presence of the stimulating antigen than the PBL of LC chicks. Peripheral blood lymphocytes (PBL) obtained from HC-line chicks exhibited a higher proliferative response to concanavalin A (Con A)-, phytohemagglutinin (PHA)- or pokeweed mitogen (PWM)-stimulation than LC PBL. These results demonstrate that the selection for high or low antibody response to E. coli at a young age resulted also in a significant change in the response of other parameters of the immune system. The high response to E. coli was found to be associated with a high antibody response to other antigens (NDV and SRBC), increased phagocytic activity and increased proliferative response to antigen or mitogens. The selection most probably affected early immunocompetence.     

Effect of genetic selection and MHC haplotypes on lymphocyte proliferation and interleukin-2 like activity in chicken lines selected for high and low antibody production against sheep red blood cells

Chickens from third generation matings of lines of chickens selected for high (HA) and low (LA) antibody production to sheep red blood cells (SRBC) and typed for MHC genotypes B13/13, B13/21, and B21/21 were used in this study. Chickens from both lines carried all the three genotypes B13/13, B13/21, and B21/21. To study T- and B-lymphocytes mitogenic activity, 12-week-old female chickens were injected intravenously with 0.2 ml of 9% SRBC and spleens were collected at 0, 6 h, and 6 day post-antigen injection (pAg). Isolated lymphocytes were incubated with either Concanavalin-A (Con-A) for T-cell activity, or Pokeweed mitogen (PWM) for B-cell activity and thymidine 3H uptakes were measured. To study the Interleukin-2 (IL-2)-like activity in the same lines and genotypes, splenic lymphocytes from 12-week-old chickens were passed through nylon wool columns to enrich the T-cell population. After a 24 h incubation with Con-A, the conditioned media (CM) were collected. The CM were tested for IL-2 like activity by determining whether they altered the proliferation of Con-A stimulated T cells. This proliferation effect was then compared to that of a reference conditioned media (RCM) prepared from K-strain birds and that were used as the standard for the assay. There was no significant difference (p > 0.05) in IL-2 like activity between HA and LA lines, however, the LA was significantly higher than HA (p < 0.05) in T- and B-cell mitogenic activity. The genotype B13/13 had significantly higher (p < 0.05) IL-2 like activity than the B21/21. The genotype B13/13 was also significantly higher (p < 0.05) in T- and B-cell mitogenic activity than the B21/21. At 0 h, pAg T- and B-mitogenic activity was significantly higher (p < 0.05) than 6 h. In summary, our results indicate that although the birds were selected for high antibody production to SRBC, their lymphocyte mitogenic activity was lower than those selected for low antibody production. Hence, humoral and cell-mediated immune responses appear to be under different genetic controls, and that selection for greater humoral response may be at the expense of cellular responses. Our results also suggest differences in IL-2 like activity production between chickens carrying different MHC B-haplotypes, and that genetic control of such activity is possibly linked to the MHC genes.     

Rates of muscle protein breakdown in chickens selected for increased growth rate, food consumption or efficiency of food utilisation as assessed by N tau-methylhistidine excretion

1. N tau-methylhistidine excretion, growth rate, food consumption and body composition was determined in 12 4 to 5 week old chickens sampled from each of 4 lines selected for increased body-weight gain (line W), for increased food consumption (line F), for improved efficiency of food utilisation (line E) or at random (line C), after 12 generations of selection. 2. The use of N tau-methylhistidine as an index of myofibrillar protein breakdown was validated in male and female chickens of lines E and F by following the fate of injected N tau-(14CH3)methylhistidine. Most of the radioactivity (79.3 +/- 1.1%) was excreted in 4 d, with the remainder retained in the carcase. In excreta, 94 +/- 2% of the radioactivity was associated with free N tau-methylhistidine and for the carcase, this value was 88 +/- 3%. 3. In the main experiment, final body weights averaged 497, 651, 588 and 537 g and food: gain ratio averaged 2.47, 2.21, 3.14 and 2.06 for lines C, W, F and E respectively, Carcase protein content (g/100 g body weight) was not different between the lines. 4. N tau-methylhistidine excretion was 5.86, 5.48, 6.43 and 4.99 mumoles/mole carcase-N/d for lines C, W, F and E, respectively. The rate for line F was significantly higher than for lines W and C and that for line E was significantly less than for the control line. 5. The N tau-methylhistidine excretion rate was positively correlated with food: gain ratio. 6. Selection for rapid growth, high food consumption or improved food utilisation results in changes in N tau-methylhistidine excretion which suggest proportionate changes in muscle protein turnover.     

Antibody transmitting ability of hens from lines of chickens differing in response to SRBC antigen

1. Hens from White Leghorn lines selected for high (HA) or low (LA) antibody response to sheep red blood cells (SRBC) were inoculated with 0.1 ml of either 0.25% or 2.50% SRBC suspension. Eggs laid over the next 15 d were grouped into 5, 3‐d collection periods and incubated. Maternal antibody titres were determined in chicks at hatch and 7 d after hatch.

2. In a subsequent experiment, hens of the 2 lines were inoculated with 0.1 ml of 2.50% suspension of SRBC, and eggs laid on days 10 to 13 after inoculation were incubated. Maternal antibody titres were determined in 15 and 18‐d embryos as well as in chicks at 0, 5, 10, 15, 20, and 25 d after hatch.

3. Dosage of SRBC had no effect on the antibody titres in line HA; however, the higher dosage elicited greater antibody titres than the lower dosage in line LA.

4. Maternal antibodies were detected earlier in chicks of line HA (eggs laid on days 7 to 9) than those of line LA (eggs laid on days 10 to 12) regardless of dosage administered to the hens.

5. In both lines, antibodies specific to SRBC were observed on day 15 of incubation, with the frequency of responders greatest at hatch. The high frequency of HA responders was maintained for 15 d after hatch, whereas there was an immediate decline with age in LA responders.

6. It was concluded that lines HA and LA have diverged in the pattern of maternal antibody levels as a result of the divergent selection for antibody response to SRBC.     

Serum haemolytic complement activities in 11 different MHC (B) typed chicken lines

To study the relation between serum complement levels and the chicken MHC (B) complex, complement haemolytic activity was measured in sera from hens from seven pure-bred B-typed White and one Brown Leghorn lines, and three ISA-Warren lines that had been divergently selected for antibody responses to sheep red blood cells (SRBC). Significant differences occurred in the serum haemolytic complement activities, both belonging to the classic (CPW) and the alternative (APW) pathways, among the 11 different haplotyped chicken lines. Hens with high CPW and high APW titres predominantly displayed the B2 or B21 haplotypes. Chickens with low CPW and APW were found in B14 and B15 haplotypes. Haplotype B14 appears to be different in complement levels when present into the pure-bred lines or into the ISA-Warren line selected for low antibody responses to SRBC. Otherwise, the presence of B21 in ISA-Warren line selected for high antibody responses to SRBC does not differ with the B21 in the inbred lines (except in the NL-line for CPW values). In general the haplotypes B2 and B21 are found in chicken lines with enhanced disease resistance, and the B15 haplotype has been connected with enhanced disease susceptibility. Our results suggest that levels of haemolytic complement activity, either from the classical or from the alternative pathways, may underlie part of the immunocompetence ascribed to the MHC (B) complex in chickens.     

Genetic control of immunity to Eimeria tenella. Interaction of MHC genes and non-MHC linked genes influences levels of disease susceptibility in chickens

The relative importance of MHC genes and background genes in the genetic control of disease susceptibility and the development of protective immunity to E. tenella infection was investigated in eight different strains of 15I5-B congenic and four inbred chicken strains. RPRL 15I5-B congenic chickens that share a common genetic background but express different B haplotypes demonstrated wide variations in disease susceptibility and the development of acquired resistance to E. tenella infection. Infection of chickens sharing a common B haplotype but expressing different genetic backgrounds showed quite contrasting levels of susceptibility to secondary E. tenella infection. In all chicken strains examined, infected chickens developed high levels of serum and biliary anti-coccidial antibodies regardless of their B haplotypes. Furthermore, no correlation between antibody levels and the phenotypically expressed levels of disease resistance was demonstrated. These findings lend support to the view that interaction of MHC genes and non-MHC genes influences the outcome of host response to E. tenella infection.     

Influence of E. coli infection on the disposition kinetic of nalidixic acid in broiler chickens.

The pharmacokinetic data of nalidixic acid were investigated in normal and E. coli infected chickens. The highest serum concentration were reached after 2 hours with t0.5 (ab) of (1.706 +/- 0.1 min in normal and 2.030 +/- 0.11 min in diseased) and (1.72 +/- 0.11 min in normal and 1.416 +/- 0.044 in diseased chickens) following oral and intramuscular administration, respectively. The elimination half-life t0.5 (beta) were (2.514 in normal and 2.35 hr in diseased) and (2.567 hr in normal and 2.672 hr in diseased) respectively. Following intravenous injection the kinetic of nalidixic acid followed two compartments open model with t0.5 of (6.27 and 9.15 hr), Vd (0.45 and 0.79 L/kg), Cltot (8.86 and 13.32 ml/kg/min) in normal and E. coli infected chickens, respectively. Administration of nalidixic acid twice daily for 5 successive days in a dose level of 25 mg/kg b. wt. by oral and intramuscular routes showed a cumulative behaviour.     

Specific antibody responses and generation of antigenic variants in chickens immunized against a virulent avian influenza virus.

To examine the specificity of the antibody response to the influenza hemagglutinin and the generation of antigenic variants, chickens were immunized against the highly virulent H5 virus A/Ty/Ont/7732/66 (H5N9) and then challenged with a lethal dose of the virus. The antibody responses of these chickens to the hemagglutinin (HA) were examined with an enzyme-linked immunosorbent assay (ELISA) in which their sera were titrated for the ability to block the binding of monoclonal antibodies (MAbs) to five distinct neutralizing epitopes on the viral HA. Based on the ELISA results, a majority (5/6) of the chickens produced antibodies to three of the five neutralizing epitopes on the viral HA. After challenge, two of six immunized chickens shed virus and died; antigenic comparisons of isolates from these two chickens indicated the presence of an antigenic variant; i.e., there was a change in one neutralizing epitope on the HA of virus shed by one chicken. None of the chickens had produced antibodies to this particular epitope on the viral HA. Inoculation of chickens with this variant resulted in 100% mortality, demonstrating that a change in this particular epitope did not alter the virulence of the virus. These studies indicate that chickens immunized against highly virulent influenza viruses may excrete virulent variants following challenge with live virus.     

The interaction between Newcastle disease virus and Escherichia coli endotoxin in chickens.

The interaction between Newcastle disease virus (NDV) and Escherichia coli endotoxin was studied in cell cultures, embryonated chicken eggs, and 8-wk-old chickens. These interactions were evaluated according to the induction of specific or nonspecific resistance in the host system and the virus titer produced in both chicken embryos and chickens. The endotoxin of E. coli induced a decrease in the size of the bursa of Fabricius in live chickens. Escherichia coli endotoxin given intravenously induced plasma antiviral activity in chickens that was interpreted to be interferon, as detected in a vesicular stomatitis virus plaque reduction assay. Endotoxin failed to produced toxic effects in the chicken embryo fibroblasts (CEFs) or to result in any antiviral effect because no change was noted in the number of NDV plaques formed in CEF cultures. When endotoxin was given 3 days before NDV exposure in chickens, the virus titers were significantly (P < 0.05) decreased from a peak of 10(2) to 10(0.18), 10(2.5) to 10(0.18), and 10(2.5) to 0 in the spleens, lungs, and kidneys, respectively, at 72 hr post-NDV inoculation. When endotoxin was given 24 hr after NDV inoculation, the NDV titer significantly (P < 0.05) increased from 10(2.0) to 10(3.5), 10(2.5) to 10(6.5), 10(2.5) to 10(4.5), 0 to 10(2.5) in the spleen, lungs, kidneys, and liver, respectively, at 72 hr after NDV inoculation. In chicken sera, hemagglutination inhibition (HI) titer to NDV was significantly (P < 0.05) enhanced from 1164 to 3127 when endotoxin was given prior to virus inoculation. However, there was a decrease in HI to NDV from 1164 to 727 without a significant difference in chicken sera when NDV was given prior to endotoxin inoculation.     

Avian eimeria: invasion in foreign host birds and generation of partial immunity against coccidiosis

Four species of avian Eimeria invaded the intestine of foreign host birds in the same areas in which they invaded the natural host. Repeated inoculation (immunization) of chickens with the turkey coccidian, Eimeria adenoeides, partially protected the chickens against a subsequent challenge with 5.8 x 10(4) E. tenella oocysts. At 6 days post-challenge, the weight gain and feed conversion efficiency of the immunized chickens was significantly better than those of the chickens that were not immunized with E. adenoeides. Lesion scores and cellular invasion by the sporozoites were significantly lower in the immunized birds than in the unimmunized group. Electrophoresis and Western blot analysis identified changes in the serum antibody profiles of the chickens that appeared to be associated with the immunization and challenge programs. An antibody or antibodies recognizing a 60,000-molecular-weight antigen of E. tenella sporozoites disappeared when chickens immunized with E. adenoeides were challenged with E. tenella; an antibody or antibodies recognizing a 23,000-molecular-weight sporozoite antigen appeared within 6 days of challenge. Reciprocal studies, in which turkeys were immunized with E. tenella and challenged with E. adenoeides, showed little evidence of protection.     

Avian influenza in ovo vaccination with replication defective recombinant adenovirus in chickens: vaccine potency, antibody persistence, and maternal antibody transfer

Protective immunity against avian influenza (AI) can be elicited in chickens in a single-dose regimen by in ovo vaccination with a replication-competent adenovirus (RCA)-free human adenovirus serotype 5 (Ad)-vector encoding the AI virus (AIV) hemagglutinin (HA). We evaluated vaccine potency, antibody persistence, transfer of maternal antibodies (MtAb), and interference between MtAb and active in ovo or mucosal immunization with RCA-free recombinant Ad expressing a codon-optimized AIV H5 HA gene from A/turkey/WI/68 (AdTW68.H5(ck)). Vaccine coverage and intrapotency test repeatability were based on anti-H5 hemagglutination inhibition (HI) antibody levels detected in in ovo vaccinated chickens. Even though egg inoculation of each replicate was performed by individuals with varying expertise and with different vaccine batches, the average vaccine coverage of three replicates was 85%. The intrapotency test repeatability, which considers both positive as well as negative values, varied between 0.69 and 0.71, indicating effective vaccination. Highly pathogenic (HP) AIV challenge of chicken groups vaccinated with increasing vaccine doses showed 90% protection in chickens receiving > or = 10(8) ifu (infectious units)/bird. The protective dose 50% (PD50) was determined to be 10(6.5) ifu. Even vaccinated chickens that did not develop detectable antibody levels were effectively protected against HP AIV challenge. This result is consistent with previous findings ofAd-vector eliciting T lymphocyte responses. Higher vaccine doses significantly reduced viral shedding as determined by AIV RNA concentration in oropharyngeal swabs. Assessment of antibody persistence showed that antibody levels of in ovo immunized chickens continued to increase until 12 wk and started to decline after 18 wk of age. Intramuscular (IM) booster vaccination with the same vaccine at 16 wk of age significantly increased the antibody responses in breeder hens, and these responses were maintained at high levels throughout the experimental period (34 wk of age). AdTW68.H5(ch)-immunized breeder hens effectively transferred MtAb to progeny chickens. The level of MtAb in the progenies was consistent with the levels detected in the breeders, i.e., intramuscularly boosted breeders transferred higher concentrations of antibodies to the offspring. Maternal antibodies declined with time in the progenies and achieved marginal levels by 34 days of age. Chickens with high maternal antibody levels that were vaccinated either in ovo or via mucosal routes (ocular or spray) did not seroconvert. In contrast, chickens without MtAb successfully developed specific antibody levels after either in ovo or mucosal vaccination. These results indicate that high levels of MtAb interfered with active Ad-vectored vaccination.     

interactions between escherichia coli and Newcastle disease virus in chickens

We investigated the interaction between Newcastle disease virus (NDV) and Escherichia coli in cell cultures, embryonated eggs, and 8-wk-old chickens. We measured the interactions on the basis of bacterial adherence and NDV hemagglutination titer in chickens, chicken embryos, and chicken embryo cell culture. Depending on the inoculation order of E. coli, a significant alteration of the growth of NDV was observed in both chickens and chicken embryos. When certain strains of E. coli were given before NDV exposure, the virus titers were lowered. In chickens, the mean virus titer was significantly (P < 0.05) lowered in the crop, the proventriculus, the gizzard, and the jejunum. However, there were no significant differences (P < 0.05) between the two groups for NDV titers in the duodenum, ileum, and cecum. In chicken embryos, when E. coli serotypes O78 and O119:B14 were inoculated before NDV exposure, the mean NDV titers were significantly (P < 0.5) lowered. However, there were no significant differences (P < 0.05) in NDV titer between the two groups when E. coli serotypes O78:K80:NM and O1ab:K NM were inoculated 24 hr before NDV exposure. When NDV was given prior to E. coli exposure, NDV titer was higher in both chickens and chicken embryos. In chickens, when NDV was given 48 hr before E. coli inoculation, NDV was detected in the proventriculus, gizzard, jejunum, ileum, and cecum, whereas no virus was detected in the control groups (NDV only). In the crop, NDV was detected at a significantly (P < 0.05) higher titer in the E. coli-inoculated group when compared with the control group that received NDV alone. In chicken embryos, virus titer was significantly (P < 0.05) higher when NDV was given 24 hr before E. coli inoculation for all three NDV strains used (Ulster and V4 strains). Adherence of E. coli to chicken embryo kidney (CEK) cells was significantly higher (P < 0.05) when the CEK cells were infected first with NDV and then by E. coli. The mean bacterial count per microscopic field in NDV-uninfected monolayers was eight compared with 112 for the NDV-infected monolayers. In approximately 10% of the fields in NDV-infected monolayers, the bacteria were too numerous to count.     

Experimental Escherichia coli respiratory infection in broilers

This study determined optimal conditions for experimental reproduction of colibacillosis by aerosol administration of avian pathogenic Escherichia coli to 2-to-4-wk-old broiler chickens. The basic model for reproducing disease was intranasal administration of approximately 10(4) mean embryo infectious dose of infectious bronchitis virus (IBV) followed by aerosol administration of an 02 or an 078 strain of E. coli in a Horsfall unit (100 ml of a suspension of 10(9) colony-forming units/ml over 40 min). Scores were assigned to groups of infected chickens on the basis of deaths; frequency and severity of lesions in the air sacs, liver and heart; and recovery of the challenge E. coli 6 days post-E. coli infection. An interval of 4 days between the IBV and E. coli challenges was best whether the chickens received the IBV at 8 or 20 days of age. Typically, 50%-80% of the chickens developed airsacculitis and 0 to 29% of the chickens developed pericarditis or perihepatitis, with little or no mortality. Escherichia coli alone resulted in no deaths and 0 to 20% airsacculitis, but these percentages increased to 0 to 5% and 52%-60% when the E. coli aerosol was administered through a cone-shaped chamber. Administration of IBV alone failed to induce lesions. Recovery of the challenge E. coli from chickens did not correlate well with lesions. On the basis of these data, administration of IBV to 20-day-old chickens followed 4 days later by exposure to an avian pathogenic E. coli reproduces avian colibacillosis with the low mortality, high percentage of airsacculitis, and low percentage of septicemic lesions characteristic of the conditions seen in the natural disease.     

Dual infections of Eimeria tenella and Escherichia coli in chickens

The interactive effects of Eimeria tenella and Escherichia coli infection in chickens were investigated. Specific pathogen free chickens inoculated orally with E tenella and challenged four days later with E coli via the air sac showed more severe acute septicaemic lesions and subacute serositis than chickens given E coli alone. Moreover, caecal lesions induced by E tenella were more severe in chickens given both E tenella and E coli than in those given E tenella alone. In contrast, oral inoculation of E coli did not result in acute septicaemic lesions or subacute serositis and had no effect on the severity of the caecal lesions caused by E tenella.     

Antibody responses of hens fed vitamin E and passively acquired antibodies of their chicks

Antibody responses of hens and their progeny were studied in commercial broiler nuclear lines. Starting at 168 days of age, individually housed pullets from lines A and B were fed a 16% crude protein and 2752 kcal metabolizable energy/kg mash diet supplemented with either 10 or 300 IU/kg of vitamin E fed as dl-alpha-tocopherol acetate. Fifty-eight days later (226 days of age), 12 hens per line-vitamin E subclass were inoculated i.v. with 0.1 ml of a 2.5% suspension of sheep red blood cells (SRBC). Plasma antibody titers were measured 6, 20, 40, 54, 70, and 88 days after inoculation. Hens from both lines were artificially mated to males from line C, and progeny from eggs collected 9-15, 25-30, and 65-70 days after inoculation were tested for antibodies to SRBC. Hens were reinoculated i.v. with 0.1 ml of 0.25% SRBC 88 days after the first inoculation, and their antibody levels were measured 3, 6, and 20 days later. Eggs laid 10-13 days after reinoculation were incubated, and antibody titers of chicks were measured at hatch. Antibody response of hens to an initial inoculation of SRBC was line-diet-time after inoculation specific. In line A, titers were greater for hens fed the lower than the higher vitamin E diet, whereas diet had no effect on the antibody levels in line B. Line effects (A > B) were observed on days 6 and 20 after inoculation but not thereafter. After the second inoculation, dietary vitamin E level had no effect on antibody levels of hens within lines, whereas a between-line difference (A > B) was observed for the lower but not the higher level of dietary vitamin E. Although there was no difference between diets for antibody transferred to progeny by line B, there was a difference (lower > higher) for line A. After reinoculation of their dams, antibody titers of chicks from line A, but not line B, reached levels similar to those after the first inoculation. Antibody levels were higher for chicks at hatch than in 16-day embryos or 10 days posthatch. The results of this research suggest genetic variation in response to immune stimulation by dietary vitamin E.     

In vitro and in vivo characterization of avian Escherichia coli. II. Factors associated with pathogenicity

The pathogenicity of 197 Escherichia coli isolates obtained from clinically affected commercially grown broiler chickens and normal hatchery chicks was assessed by inoculating day-old broilers intratracheally. The degree of pathogenicity (high, intermediate, low) was judged according to mortality and lesions occurring within 7 days following inoculation. Serotype, metabolic activity, motility, and in vitro antibiotic sensitivity of each isolate were evaluated and related to pathogenicity. Seventy-five of the isolates of high to intermediate pathogenicity belonged to serogroup O2, O78, or O35. In addition, 51 pathogenic E. coli isolates could not be serotyped, and several had multiple serotypes. Most isolates had similar metabolic activity, as determined by amino acid decarboxylation and carbohydrate fermentation, regardless of pathogenicity. An exception was the fermentation of adonitol, which occurred more frequently with the highly pathogenic strains. Motility and in vitro antibiotic sensitivity were not related to pathogenicity. An age-associated resistance to intratracheal E. coli administration occurred by 15 days of age in uncompromised birds. Relative susceptibility of birds older than 2 weeks to intratracheal and/or intravenous E. coli inoculation could be increased by prior exposure to pathogenic reovirus 1733, adenovirus 3167, or infectious bursal disease virus (IBDV). Birds infected with IBDV at 3 weeks failed to clear apathogenic and pathogenic E. coli from circulating blood.