Air Sac Lesion Scores Research Articles

Evaluation of the safety and efficacy of the novel Mycoplasma gallisepticum vaccine, Vaxsafe MG304, after spray-vaccination of 1-day-old specific pathogen-free chicks

Mycoplasma gallisepticum causes chronic respiratory disease in poultry. A novel vaccine, Vaxsafe MG304 (the ts-304 strain), has greater protective efficacy in chickens than the Vaxsafe MG (strain ts-11) vaccine when delivered by eye drop at 3 weeks of age. Applying this vaccine in the hatchery to 1-day-old birds, using mass administration methods, would improve animal welfare and reduce labour costs associated with handling individual birds. This study assessed the protection provided by vaccination with Vaxsafe MG304 after administration to 1-day-old chicks. Chicks were administered a single dose of the vaccine to assess the efficacy of either a high dose (107.0 colour changing units, CCU) or a low dose (105.7 CCU) after eye drop or spray (in water or gel) administration against experimental challenge with virulent M. gallisepticum strain Ap3AS at 7 weeks of age. The vaccine was able to colonise the palatine cleft of chicks after vaccination by eye drop (at both doses) or by spray (in water or gel) (at the high dose). The high dose of vaccine, when delivered by eye drop or spray, was shown to be safe and induced a serological response and protective immunity (as measured by tracheal mucosal thickness and air sac lesion scores) against challenge. Vaccination of 1-day-old chicks with Vaxsafe MG304 by eye drop induced protective immunity equivalent to vaccination at 3 weeks of age. Vaxsafe MG304 was also protective when applied by both coarse- and gel spray methods at the higher dose and is therefore a suitable live attenuated vaccine for use in 1-day-old chicks.

Development and evaluation of a multi-epitope subunit vaccine against Mycoplasma synoviae infection

Mycoplasma synoviae is an extremely significant avian pathogen, causing substantial financial harm to poultry farmers worldwide, and impacting both chicken and turkey production. Multi-epitope vaccines offer higher immunity and lower allergenicity compared to conventional vaccines. In this study, our objective is to develop a multi-epitope vaccine for M. synoviae (MSMV) and to evaluate the immune responses and protective efficacy of MSMV in chickens. We successfully identified a total of 14 B-cell, 5 MHC-I, and 16 MHC-II binding epitopes from the immunodominant proteins RS01790, BMP, GrpE, RS00900, and RS00275. Subsequently, we synthesized the multi-epitope vaccine by connecting all conserved epitopes using appropriate linkers. The resulting MSMV demonstrated notable antigenicity, non-allergenic properties, and stability. Notably, the MSMV effectively stimulated high levels of antibody production in chickens. Furthermore, MSMV the vaccine elicited a robust cellular immune response in chickens, characterized by a well-balanced Th1/Th2-type cytokine profile and enhanced lymphocyte proliferation. In immune protection experiments, the vaccinated chickens exhibited reduced air sac lesion scores and tracheal mucosal thickness compared to their non-vaccinated chickens. Additionally, vaccinated chickens displayed lower M. synoviae loads in throat swabs. These findings collectively suggested that the MSMV holds significant potential as a promising vaccine candidate for managing M. synoviae infections.

Screening of immunogenic proteins and evaluation of vaccine candidates against Mycoplasma synoviae

Mycoplasma synoviae (M. synoviae) is a serious avian pathogen that causes significant economic losses to chicken and turkey producers worldwide. The currently available live attenuated and inactivated vaccines provide limited protection. The objective of this study was to identify potential subunit vaccine candidates using immunoproteomics and reverse vaccinology analyses and to evaluate their preliminary protection. Twenty-four candidate antigens were identified, and five of them, namely RS01790 (a putative sugar ABC transporter lipoprotein), BMP (a substrate-binding protein of the BMP family ABC transporter), GrpE (a nucleotide exchange factor), RS00900 (a putative nuclease), and RS00275 (an uncharacterized protein), were selected to evaluate their immunogenicity and preliminary protection. The results showed that all five antigens had good immunogenicity, and they were localized on the M. synoviae cell membrane. The antigens induced specific humoral and cellular immune responses, and the vaccinated chickens exhibited significantly greater body weight gain and lower air sac lesion scores and tracheal mucosal thicknesses. Additionally, the vaccinated chickens had lower M. synoviae loads in throat swabs than non-vaccinated chickens. The protective effect of the RS01790, BMP, GrpE, and RS00900 vaccines was better than that of the RS00275 vaccine. In conclusion, our study demonstrates the potential of subunit vaccines as a new approach to developing M. synoviae vaccines, providing new ideas for controlling the spread of M. synoviae worldwide.

Virulence factors of Mycoplasma synoviae: Three genes influencing colonization, immunogenicity, and transmissibility.

Infections caused by Mycoplasma synoviae are major welfare and economic concerns in poultry industries worldwide. These infections cause chronic respiratory disease and/or synovitis in chickens and turkeys leading to reduced production and increased mortality rates. The live attenuated vaccine strain MS-H (Vaxsafe® MS), commonly used for protection against M. synoviae infection in many countries, contains 32 single nucleotide variations compared to its wildtype parent strain, 86079/7NS. Genomic analysis of vaccine strains reisolated from flocks following the administration of MS-H has identified reversions to the original 86079/7NS sequence in the obgE, oppF and gapdh genes. Here, three MS-H field reisolates containing the 86079/7NS genotype in obgE (AS2), obgE and oppF (AB1), and obgE, oppF and gapdh (TS4), as well as the vaccine MS-H and the parental strain 86079/7NS were experimentally inoculated to chickens. The strains were assessed for their ability to infect and elicit immune responses in the recipient chickens, as well as in naïve in-contact chickens. Despite the loss of temperature sensitivity phenotype and colonization of the reisolates in the lower respiratory tract, there was no significant differences detected in the microscopic mucosal thickness of the middle or lower trachea of the inoculated chickens. Concurrent reversions in ObgE, OppF and GAPDH proteins were associated with higher gross air sac lesion scores and increased microscopic upper-tracheal mucosal thickness in chickens directly inoculated with the reisolates following intratracheal administration of a virulent strain of infectious bronchitis virus. The gross air sac lesions of the chickens in-contact with those inoculated with reisolates were not significantly different to those of chickens in-contact with MS-H inoculated chickens, suggesting that horizontal transmission of the reisolates in the poultry flock will not lead to higher pathogenicity or clinical signs. These results suggest a significant role of GAPDH and/or cumulative effect of ObgE, OppF and GAPDH on M. synoviae pathogenicity. Future experiments will be required to investigate the effect of single mutations in gapdh or oppF gene on pathogenicity of M. synoviae.

Andrographolide restored production performances and serum biochemical indexes and attenuated organs damage in Mycoplasma gallisepticum-infected broilers

ABSTRACT 1. This study aimed to study the preventive and therapeutic effects of andrographolide (Andro) during Mycoplasma gallisepticum HS strain (MG) infection in ArborAcres (AA) broilers. 2. The minimum inhibitory concentration (MIC) of Andro against MG was measured. Broiler body weight, feed efficiency, morbidity, cure rate and mortality were recorded during the experiment. Air sac lesion scores and immune organ index were calculated. Expression of pMGA1.2 in lung tissue and serum biochemical indices were examined. Histopathological examinations of immune organs, liver, trachea and lung tissue were conducted by Haematoxylin and Eosin stain. 3. MIC was 3.75 μg/mL and Andro significantly inhibited the expression of pMGA1.2 (P ≤ 0.05). Compared with control MG-infected group, Andro low-dose and high-dose prevention reduced the morbidity of chronic respiratory disease in 40.00% and 50.00%, respectively. Mortality of C, D and E group was 16.67%, 10.00% and 6.67%, respectively. Cure rate of E, F, G and H group was 92.00%, 92.86%, 93.33% and 100.0%, respectively. Compared with control MG-infected group, Andro treatment significantly increased average weight gain (AWG), relative weight gain rate (RWG) and feed conversion rate (FCR) at 18 to 24 days (P ≤ 0.05). Compared with control group, Andro alone treatment significantly increased AWG in broilers (P ≤ 0.05). 4. Compared with control MG-infected group, Andro significantly attenuated MG-induced air sac lesion, immune organs, liver, trachea and lung damage in broilers. Andro alone treatment did not induce abnormal morphological changes in these organs in healthy broilers. Serum biochemical analysis results showed, comparing with control MG-infected group, Andro significantly decreased the content of total protein, albumin, globulin, alanine aminotransferase, aspartate aminotransferase, total bilirubin, urea, creatinine, uric acid, total cholesterol, and increased the albumin/globulin ratio and content of alkaline phosphatase, apolipoprotein B and apolipoprotein A-I in a dose-dependent manner (P ≤ 0.05). 5. Andro could act as a potential agent against MG infection in broilers.

Evaluation of Glycyrrhizic Acid Therapeutic Effect and Safety in Mycoplasma gallisepticum (HS Strain)-Infected Arbor Acres Broilers.

Simple SummaryMycoplasma gallisepticum (MG) can induce chronic respiratory disease (CRD) in chickens. Glycyrrhizic acid (GA) is the major ingredient of licorice and shows excellent anti-pathogenic microorganism and anti-inflammatory properties. Based on above, this study has evaluated the therapeutic effects and safety of GA in MG-infected broilers. Study results showed that GA could inhibit the proliferation of MG in vitro and expression of MG adhesion protein (pMGA1.2) in broiler lungs. GA restored production performances and attenuated MG-induced organ damage and abnormal biochemical indicator changes in MG-infected broilers. In conclusion, GA displayed significant therapeutic efficacy regarding MG infection and had no adverse effects on broilers (100 mg/kg/d).This study was conducted to evaluate the therapeutic effects and safety of GA in MG-infected broilers. Our results showed that the minimum inhibitory concentration of GA was 31.25 μg/mL. Moreover, GA inhibited the expression of MG adhesion protein (pMGA1.2) in the broilers’ lungs. GA treatment clearly decreased the morbidity of CRD and mortality in the MG-infected broilers. Compared with the model group, GA treatment significantly decreased gross air sac lesion scores and increased average weight gain and feed conversion rate in the MG-infected broilers. Histopathological examination showed GA treatment attenuated MG-induced trachea, immune organ and liver damage in the broilers. Moreover, GA treatment alone did not induce abnormal morphological changes in these organs in the healthy broilers. Compared with the model group, serum biochemical results showed GA treatment significantly decreased the content of total protein, albumin, globulin, alanine aminotransferase, aspartate aminotransferase, total bilirubin, creatinine, uric acid, total cholesterol, and increased the content of albumin/globulin, alkaline phosphatase, apolipoprotein B and apolipoprotein A-I. In conclusion, GA displayed a significant therapeutic efficacy regarding MG infection and had no adverse effects on the broilers (100 mg/kg/d).

Protective Potential of an Autogenous Vaccine in an Aerogenous Model of Escherichia coli Infection in Broiler Breeders.

In poultry, Escherichia coli is a common cause of high-cost infections. Consequently, autogenous vaccines are often used despite limited and conflicting evidence on their effectiveness have been presented. The present study aimed to investigate the efficacy of a commonly used autogenous vaccine, previously deemed ineffective, in an aerosol model of colibacillosis. Methods: Broiler breeders (n = 47) were randomly allocated to one of four groups (vaccinated and unvaccinated birds receiving an autogenous vaccine or sterile saline intramuscularly) and challenged with either aerosolised E. coli or vehicle at 29 weeks of age. Two days following inoculation, the birds were euthanised, thoroughly necropsied, and samples for bacteriology and histopathology were collected. Results: Vaccinated birds had a significantly lower bacteriology score compared to the unvaccinated group challenged with E. coli (p < 0.01) and a lower overall air sac lesion score (p < 0.05). Overall lung and spleen lesion scores only differed significantly between the unvaccinated E. coli challenged group compared to the vehicle inoculated groups. The overall gross pathology score was 2.8 and 1.95 in the unvaccinated and vaccinated E. coli challenge groups, respectively, whereas the vaccinated vehicle group had a score of 0.9 and the unvaccinated vehicle group a score of 1. Conclusions: A protective effect of an autogenous vaccine was found utilising an aerogenous model of colibacillosis through multiple methods of evaluation. The findings encourage the continued use of autogenous vaccines and underlines the necessity of discriminative experimental models with high predictive validity when evaluating vaccine interventions.

Effects of immunosuppression on the efficacy of vaccination against Mycoplasma gallisepticum infection in chickens

Immunosuppression can increase the susceptibility of chickens to other disease-causing pathogens and interfere with the efficacy of vaccination against those pathogens. Chicken anaemia virus (CAV) and infectious bursal disease virus (IBDV) are common causes of immunosuppression in chickens. Immunosuppression was induced by experimental infection with either CAV or IBDV to assess the effect of immunosuppression on the efficacy of vaccination with Mycoplasma gallisepticum strain ts-304 against infection with virulent M. gallisepticum, a common bacterial pathogen of chickens worldwide. Birds were experimentally infected with either CAV or IBDV at 1 week of age, before vaccination and challenge with M. gallisepticum to examine the effect of immunosuppression at the time of vaccination, or at 6 weeks of age, after vaccination against M. gallisepticum but before challenge with virulent M. gallisepticum, to investigate the effect of immunosuppression at the time of challenge. All birds were vaccinated with a single dose of the ts-304 vaccine at 3 weeks of age and experimentally challenged with the virulent M. gallisepticum strain Ap3AS at 8 weeks of age. In immunosuppressed chickens there was a reduction in protection offered by the ts-304 vaccine at two weeks after challenge, as measured by tracheal mucosal thicknesses, serum antibody levels against M. gallisepticum, air sac lesion scores and virulent M. gallisepticum load in the trachea. Immunosuppressed birds with detectable serum antibodies against M. gallisepticum were less likely to have tracheal lesions. This study has shown that immunosuppression caused by infection with CAV or IBDV can interfere with vaccination against mycoplasmosis in chickens.

Duration of protective immunity induced by Mycoplasma gallisepticum strain ts-304 vaccine in chickens

Mycoplasma gallisepticum (MG) is an important pathogen of poultry worldwide, causing chronic respiratory disease in chickens and turkeys. MG ts-304 is a GapA positive clone recovered from Vaxsafe MG (strain ts-11) that has been shown to be safe in chickens when delivered by the eye drop route to 3-week-old specific-pathogen-free chickens and to confer protection against challenge at 4 weeks after vaccination, as measured by tracheal mucosal thickness and air sac lesion scores. In this study, specific pathogen-free chickens (SPF) were vaccinated with a single dose of the MG ts-304 vaccine (106.0 colour changing units) at 3 weeks of age and experimentally challenged by aerosol with the virulent M. gallisepticum strain Ap3AS at 40, 48 and 57 weeks after vaccination. There were no significant differences in tracheal mucosal thickness 2 weeks after challenge between chickens challenged at the three time points, or between the vaccinated birds after challenge and unvaccinated/unchallenged control birds. Thus there was clear evidence that the immunity conferred by vaccination with the MG ts-304 vaccine resulted in significant protection against tracheitis in chickens that extended to, but was highly likely to exceed, 57 weeks after vaccination and that similar long term protective immunity could be expected to be conferred by a vaccine dose lower than that used in this study.

Pharmacokinetics, tissue residues of tilmicosin phosphate (tilmicor-al®) and its in vitro and in vivo evaluation for the control of Mycoplas-ma gallisepticum infection in broiler chickens

The aim of present study was to determine the pharmacokinetics and tissue residues of tilmicosin phosphate (tilmicoral®) as well as its in vitro and in vivo evaluation for control of Mycoplasma gallisepticum (MG) infection in broiler chickens. Pharmacokinetics (single oral dose) and tissues residues (daily for five days) of tilmicosin (25 mg/kg b.wt) in broilers were investigated. Peak plasma concentration of tilmicosin was 1.25±0.0.09 μg/mL and achieved at 3.15±0.34 h. Elimination half-life was long (44.3±7.22 h) and Vdarea was large (1.25±0.082 L/kg). Residue study revealed a good distribution and penetration of tilmicosine in lung, liver, kidney and muscles. Tilmicosin could not be detected in all tested tissues (except in lung) at 6 days after last administration. The MIC of tilmicosin and tylosin against MG were 0.054 and 0.319 μg/mL, respectively. MG infected chickens and treated by tilmicosin or tylosin showed a significant (p&lt;0.05) improvement in mean body weights gain and a significant (p&lt;0.05) decline in mean clinical signs score, air sac lesion score and mortality rate, however tilmicosin was a superior drug. In conclusion, timicoral® was a very effective medication for controlling MG infection in broiler chickens due to its rapid absorption, long elimination half-life, rapid and extensive penetration from blood into tissues especially lungs and air sacs. Additionally, tilmicoral® had a short withdrawal time. Moreover, its superior efficacy (in vitro and in vivo) against MG.

The efficacy of Mycoplasma gallisepticum K-strain live vaccine in broiler and layer chickens

The efficacy of a live Mycoplasma gallisepticum (MG) vaccine candidate (K-strain) was compared to commercially available vaccines in broiler-type chickens (Trial 1) and layer-type chickens (Trial 2). In Trial 1, three-week-old broiler-type chickens were vaccinated via aerosol with K-strain or an F-strain vaccine. The vaccinated chickens and 10 non-vaccinated controls were subsequently challenged with virulent R-strain via aerosol at six weeks post vaccination; both K-strain and F-strain vaccination resulted in significant protection from air sac and tracheal lesions, as well as R-strain colonization (P ≤ 0.05). In Trial 2, commercial layer-type chickens were vaccinated with ts-11 (via eye drop) or K-strain (via aerosol) at 12 weeks of age. At 25 weeks of age these birds were challenged with R-strain via aerosol. The ts-11 and K-strain vaccinated groups both had significantly lower air sac lesion scores and a lower prevalence of ovarian regression after challenge as compared to non-vaccinated chickens (P ≤ 0.05). K-strain vaccination also prevented significant tracheal lesions and R-strain colonization (P ≤ 0.05). K-strain shows great potential as a highly efficacious live MG vaccine in broiler and layer-type chickens for protection of the respiratory and reproductive systems as well as prevention of infection with field strains.

Development of a Mycoplasma gallisepticum infection model in turkeys

Mycoplasma gallisepticum causes chronic respiratory disease in chickens and is also highly pathogenic in turkeys. Several live attenuated M. gallisepticum vaccines are available for prevention of disease in chickens but they are considered to be either not safe or not efficacious in turkeys. The studies presented here aimed to develop a suitable infection model in turkeys, a prerequisite for development of a vaccine against M. gallisepticum for turkeys. Two wild-type Australian M. gallisepticum strains, Ap3AS and 100809/31, were used and their capacity to induce lesions was evaluated in 5-week-old to 6-week-old turkeys exposed to aerosols of these strains. Gross air sac lesion scores in the group exposed to Ap3AS were significantly greater than those in the group exposed to 100809/31 (P < 0.05). Histological tracheal lesion scores and tracheal mucosal thicknesses were significantly greater in birds exposed to either strain than in the unexposed birds (P < 0.05), but no significant differences were observed between the two infected groups. In a subsequent experiment, 6-week-old to 7-week-old turkeys were exposed to different doses of M. gallisepticum Ap3AS. Serology and M. gallisepticum re-isolation performed 14 days after infection showed that all birds exposed to Ap3AS were positive by rapid serum agglutination and by culture. Gross air sac lesion scores in the groups exposed to the highest dose, 8.17 × 108 colour-changing units Ap3AS/ml, as well as a 10-fold lower dose were significantly more severe than in the uninfected control group. Lesion scores and tracheal mucosal thicknesses were significantly greater in birds exposed to Ap3AS than in the unexposed birds (P < 0.05). However, no significant differences were seen in tracheal mucosal thicknesses or lesion scores between the groups exposed to the different doses of Ap3AS. This study has established a reliable challenge model for M. gallisepticum infection in turkeys, which will be useful for evaluation of potential M. gallisepticum vaccine candidates for this species.

The In-vitro and In-vivo Evaluation of Tiamulin and Tilmicosin for the Treatment of Mycoplasma gallisepticum Infected Broiler Chickens

This study was undertaken to evaluate the efficacy of some antimicrobials containing tiamulin and tilmicosin (as active principles) against Mycoplasma gallisepticum (MG) infection both in-vitro and in-vivo. For in-vitro investigation, the Minimum Inhibitory Concentration (MIC) of tiamulin and tilmicosin against MG organism was done. However, the in-vivo evaluation of tiamulin and tilmicosin against field MG infection was carried out on a commercial broiler chicken farm taken from MG infected farm and proved to have such infection through bacteriological and serological examination at day old. Once the birds suffered from respiratory signs at 22 days of age, this flock was divided into three separate houses. Chickens in house (1) were kept as MG-infected without treatment; chickens in the house (2) were treated with tiamulin in the drinking water (1 gram/1.5 liter) for 3 successive days and the birds in house (3) were also treated with tilmicosin in the drinking water (0.3 ml/liter) for 3 successive days. Just after appearance of the first clinical signs and mortalities, the clinical signs score was recorded, the birds were weighed and the serum samples were collected for serological examination. The clinical signs and the mortalities in each house were recorded daily during and after the treatment course till the end of the study (42 days of age). The body weight of the birds in each house was determined weekly till 6 weeks of age. Twenty birds from each house were sacrificed weekly for recording the air-sac lesion score and for re-isolation of MG. The air-sac lesion score and the re-isolation of MG were also detected from the dead birds. Serum samples were collected from sacrificed 20 birds just after appearance of clinical signs and from each house at the end of the work (42 days of age) for detecting the presence of antibodies for MG infection using serum plate agglutination test. The results of the in-vitro assessment revealed that the MIC of tiamulin and tilmicosin (μg/ml) was 0.1 and 0.05; respectively. In-vivo evaluation of tiamulin and tilmicosin denoted that there were significant (p<0.05) differences between MG-infected non-treated house and the treated houses, Tiamulin and tilmicosin succeeded in inducing significant reduction (p<0.05) in the mean clinical score, mortality rate, mean gross air-sac lesion score, re-isolation rate of MG and absence of MG antibodies in the treated houses than the infected control group. Moreover, significant (p<0.05) improvement in the mean body weights was observed in the treated chickens than the infected ones. Both tiamulin and tilmicosin were efficacious in the treatment of MG infection in broiler chickens; nevertheless tilmicosin medication was superior in controlling of such infection. It is recommended that testing the efficacy of the drugs in-vitro before application in-vivo to overcome the problem of drug resistance, also tiamulin and tilmicosin are effective in eradication programmes of field MG infection in the broiler chickens.

Interaction between genotype and dietary concentrations of methionine for immune function in commercial broilers

1. Growth, antibody response to sheep red blood cells (SRBC) and resistance to Escherichia coli were measured in broiler female chicks received from 4 (n = 100 in each) commercial genotypes (A, B, C and D) and fed with maize-soybean-deoiled rice bran based diets containing 4 concentrations of methionine (3·91, 4·46, 5·00 and 5·54 g/kg). The diets were fed ad libitum from 1 to 49 d of age. 2. Body weight gain and weight gain/food intake at 2 week intervals, response of broilers to inoculation of 0·5 ml of SRBC (0·5 or 2·5%), 0·1 ml of E. coli (10−4 dilutions) culture, and 100 µg phytohaemogglutinin-P (PHA-P) at 43 d of age were measured. The responses to SRBC and E. coli inoculation were recorded at 5 d post inoculation (PI), while the responses to PHA-P were recorded at 12 and 24 h PI. 3. Genotype by methionine interaction was not significant for body weight gain, but significant differences in weight gain were observed among different genotypes. Variation in methionine concentration did not influence body weight gain or weight gain/food intake at 1 to 14, or 42 d of age. At 28 d of age, chicks fed on the 3·91 g methionine/kg diet weighted significantly less than those on the other methionine concentrations. Genotype by methionine interaction was observed for food efficiency at 0 to 28 d of age but not at other ages. 4. Antibody titres against SRBC and heart and air sac lesion score to E. coli challenge were not influenced by genotype-methionine interaction. Chicks given higher concentrations of methionine had higher antibody titres and greater cutaneous basophilic hypersensitivity (CBH) response than those given low levels of methionine. Also, variation was observed in expression of CBH response to PHA-P among different genotypes. 5. It may be concluded that, although the commercial broiler chicks do not require more than 3·91 g methionine/kg for optimum growth and food efficiency, the immunity in terms of CBH response and antibody production to SRBC increased with the concentration of methionine in the diet in the majority of genotypes, indicating a higher methionine requirement for immunity than for weight gain.

Safety, immunogenicity, and efficacy of two Escherichia coli cya crp mutants as vaccines for broilers.

Attenuated derivatives (delta cya delta crp mutants) of an O2 and an O78 avian septicemic Escherichia coli strain were used to immunize broiler chickens by spray to determine the safety, immunogenicity, and efficacy of the derivatives in single- and double-dose regimens. In the safety and immunogenicity studies, groups of 10 chickens were vaccinated by spray (droplet size approximately 20 microm) with the parent E. coli, the mutant organisms, or phosphate-buffered saline (PBS) at 14 days of age and euthanatised 21 days later. There was no deaths or gross pathologic finding in any of the chickens immunized with the vaccine strains. Compared with the levels in chickens exposed to PBS, there were significantly higher levels of immunoglobulin (Ig) G antibody in serum and air sac washings and of IgA antibody in air sac washings in response to the virulent parent strains than to the vaccine strains. In efficacy studies, chickens were immunized with the O2 or the O78 vaccine strain or PBS at day 14 and with the O2 vaccine strain or PBS at days 10 and 14 and challenged with the parent strain 10 days after the last vaccination. There was no significant difference in local IgA and IgG and serum IgG responses between vaccinated and control groups. Chickens vaccinated with the O2 strain, but not the O78 strain, had significantly lower air sac lesion scores compared with those of the unvaccinated groups in both single- and double-dose regimens. We conclude that the mutant O2 strain provided moderate protection against airsacculitis.

Genotype by Dietary Lysine Interaction for Growth and Response to Sheep Red Blood Cells and Escherichia coli Inoculation in Commercial Broiler Chicks

An experiment was conducted to assess the interaction between genotypes and dietary lysine content in commercial broiler chicks by measuring growth, and response to sheep red blood cells (SRBC) and Escherichia coli (E.coli) inoculation. Female chicks from four genotypes (A=Anak 2000; B=Hubbard; C=Cobb and D=Synthetic broiler) were fed four levels of lysine in diet from d old till the end of experiment. The lysine content of the diet was 9.61, 10.51, 11.41 and 12.31 g/kg. Body weights at 0, 14, 28 and 42 d of age and pen-wise feed intake till 14, 28 and 42 d of age were recorded. Production of antibody against SRBC and resistance to E.coli were measured at 5 d of post inoculation (PI) at 43 d of age. Also, response to phytohemaglutinin-P (PHA-P) was measured at 12 and 24 h of PI at 48 d of age. Genotype by dietary lysine interaction was significant for body weights at 14 and 28 d of age, but not at 42 d of age. Genotype by dietary lysine interaction was not significant for feed efficiency, for antibody titers against SRBC, and for air sac lesion score, relative bodyweight change, and relative weights of bursa and spleen in response to E.coli inoculation. However, a significant interaction was observed between the levels of lysine and dosage of SRBC for antibody titers. There was significant genotype by dietary lysine interaction for cutaneous basophilic hypersensitivity (CBH) response to PHA-P at 12 and 24 h of PI. It may be concluded that to obtain optimum body weight and immunity in commercial broilers the dietary lysine requirement may be recommended specific to the genotype. (Asian-Aust. J. Anim. Sci. 2002. Vol 15, No. 8 : 1170-1177)

Use of lipopolysaccharide (LPS) as a positive control for the evaluation of immunopotentiating drug candidates in experimental avian colibacillosis models

The aetiologic agent of avian colibacillosis isEscherichia coli. Colibacillosis is a disease that causes mortality and production performance problems in chickens which results in economic losses for the poultry industry. It will be increasingly important for scientists to identify novel solutions that can be implemented which will provide poultry producers with a tool to manage this economically important disease. The purpose of this investigation was to determine whether lipopolysaccharide (LPS) could be used as a positive control to evaluate novel chemistries for immunopotentiator activity in battery or floor-pen avian colibacillosis models in chickens. In the battery study, subcutaneous administration ofLPSto one-day-old broiler cockerels caused a significant reduction (P < 0.003) in all parameters of colibacillosis evaluated, i.e. mean air sac lesion scores, per cent air sac lesions,E colire-isolation and per cent mortality. However, in the floor-pen study, subcutaneous administration to one-day-old broiler chicks resulted in a numerical, but not stastically significant reduction (P < 0.1) in mortality associated with colibacillosis. These data indicate thatLPScan be used as a positive control to evaluate the efficacy of immunopotentiator drug candidates in avian colibacillosis models.

Effect of Poultry Litter Treatment® (PLT®) on the development of respiratory tract lesions in broilers

In previous studies, Poultry Litter Treatment® (PLT®) was shown to reduce atmospheric ammonia levels and ascites death rates, and produce higher profit value in broiler chickens. The purpose of the present study was to determine the effect of PLT® on atmospheric ammonia levels, the development of respiratory tract lesions, and body weight gains in broiler chickens. Data were collected from chicks that were raised in containment conditions that resembled commercial settings. Atmospheric ammonia levels, gross thoracic air sac lesion scores, and the numbers and magnitudes of histopathologic trachéal mucosal injuries were significantly (P = 0.001) reduced in chickens that were raised on PLT®‐treated litter than in their untreated‐litter control counterparts. In addition, mean body weights and lung:body weight ratios were significantly (P < 0.03) larger in broilers that were raised on treated litter. The reductions in respiratory tract lesions among broilers raised on PLT®‐treated litter were attributed to reductions in atmospheric ammonia levels.

The Effect of Oxytetracycline on the Severity of Airsacculitis in Chickens Infected with Mycoplasma gallisepticum

Four groups of mycoplasma-free commercial broilers were challenged with the R strain of Mycoplasma gallisepticum (MG) at 14 days of age. Groups received feed containing either no medication, or 500 ppm or 1000 ppm oxytetracycline (OTC) beginning at age 13 days, or 1000 ppm OTC beginning at age 15 days. All broilers were vaccinated with a live mild Massachusetts infectious bronchitis vaccine at 17 days of age. Air sac lesions were scored at age 24 days. In two almost identical experiments, all OTC treatment groups had significantly lower mean air sac lesion scores than the unmedicated challenged controls. Groups that were fed 1000 ppm OTC in feed had significantly lower mean air sac lesion scores than groups that were fed 500 ppm OTC in feed. There was no significant difference in mean air sac lesion scores between the groups fed 1000 ppm OTC in feed beginning at 13 days of age and those fed 1000 ppm OTC in feed beginning at 15 days of age.

Comparison ofin vivoandin vitromethods for pathogenicity evaluation formycoplasma gallisepticumin respiratory infection

This study was designated to examine the pathogenicity of several strains of Mycoplasma gallisepticum (R, F, S-6, 227 and A5969) and laboratory derived substrains. Preliminary results indicated that the nine M. gallisepticum strains differed markedly in their pathogenicity for chickens. A comparison was made between various in vivo and in vitro methods for quantitative evaluation of pathogenicity. Reproducibility, convenience, and relevance to clinical observations were considered. Two in vivo tests were employed. In one case 2-week-old chickens were infected with M. gallisepticum by aerosol. Air sac lesion score, ability to reisolate M. gallisepticum from trachea and air sac, and serological response to M. gallisepticum were determined 2 weeks post infection. The second test was based on the ability to reisolate M. gallisepticum 3 days after intratracheal inoculation at different dose levels. In this way it was possible to calculate a median tracheal infection dose for each of the strains tested, a parameter which reflected their ability to colonise this organ. Scanning electron microscopy (SEM) was used to examine changes in the surface morphology of the infected trachea and photometric analysis of the SEM lesion was performed. Certain strains multiplied profusely in the trachea of healthy birds without causing detectable pathological changes. Chick tracheal ring (TR) cultures were used for estimating pathogenicity in vitro. In the standardised TR system a method for quantitative evaluation of mycoplasma-TR interaction was devised. The use of the TR system as a model for evaluating in vitro pathogenicity was rapid and less subject to environmental variation than the in vivo tests. The test was economical with respect to time, space and birds.