The comparative and sequential histopathology of different tissues of unvaccinated laying hens and cockerels were studied in chickens exposed to T and N1/88 strain of infectious bronchitis virus (IBV). The Harderian gland and trachea of hens and cockerels in both T- and N1/88-infected groups were damaged to a similar extent. The cecum was unaffected for both strains of IBV in both hens and cockerels. The sequential histopathological changes in hens revealed that IBV multiplies initially in the Harderian gland, then in the tracheal mucosa and simultaneously in the kidney and regions of the oviduct such as the magnum, tubular shell gland, and shell gland pouch. In cockerels, IBV multiplies first in the Harderian gland, then simultaneously in the trachea and kidney. Overall, the severity and persistence of lesions were greater in the kidneys of T-infected hens as compared with N1/88-infected hens. However, pathological changes in the kidney were mild in T- and N1/88-infected cockerels.

Infectious bronchitis virus (IBV) strains primarily infect the epithelial tissues of the respiratory tract and kidneys but they also multiply in the egg forming region of the oviduct, causing paleness of shell colour in brown egg laying hens. Protoporphyrin IX (PP IX) is the main eggshell pigment in the eggs of laying hens, in addition to other pigments such as biliverdin. The brown pigment has a number of functions including specific gram positive antibacterial action and positive influence on consumer perceptions. The aim of the current study was to assess any significant effect of different IBV strains on the shell colour in brown shelled eggs. Eggs were collected from day 2 to day 22 post infection (p.i) from unvaccinated and vaccinated laying hens challenged with IBV wild strains (T and N1/88) and vaccine strains (A3 and Vic S) in addition to a control group hens. Eggshells were processed for measurement of shell reflectivity (%), spectrophotometry (SCI L* component), and protoporphyrin IX (PP IX) quantification from shells with and without cuticle. There was a significant effect (P<0.05) of day p.i and viral strain on shell reflectivity, SCI L* and PP IX in eggshells with and without cuticle. The values for shell reflectivity and SCI L* increased and those for PP IX decreased with increased day p.i until day 12, suggesting an increasing viral load in the shell gland. The shell reflectivity and L* values decreased insignificantly after day 12 and slightly increased again towards day 22. The amount of PP IX tended to increase after day 12 p.i. but this was not statistically significant, suggesting that after day 12 p.i., the viral load started declining and thus shell colour was restoring in the challenged hens. The higher shell reflectivity and SCI L* values, and lower PP IX values, of eggshells from T and N1/88 followed by Vic S strain infected birds suggests that the T strain was most severe in its effect followed by N1/88 and Vic S with A3 being the more mild one. The values of shell reflectivity, SCI L* and PP IX were not significantly different for eggshells from unvaccinated and vaccinated laying hens in the whole eggshell, but were significant in shells from which cuticle had been removed.

Microbial populations from samples of six pooled eggs were enumerated for Enterobacteriaceae on violet red bile glucose agar (Oxoid, Australia) plates with overlay (purple-red colonies). Presumptive colonies were counted and reported as log cfu/mL of egg rinsate. Translucency tended to be higher in late lay flocks. The Enterobacteriaceae count on the egg shell surface was slightly higher in late lay flocks but was not significantly different from that of the flocks in early lay. 'Salmonella' Infantis was isolated from egg shell rinse. Samples were collected throughout the year 2010-2011. This study is on-going so, as the sample size increases, new insights will be obtained.

The effect of two strains of infectious bronchitis virus (IBV-T and N1/88 strains) on internal and external quality of eggs was studied in unvaccinated Isa Brown hens in full lay. Overall, there was no decline in egg production in either of the infected groups. Long-lasting effects were observed on egg internal quality of T strain-infected hens. Effects on internal quality in the N1/88 strain-infected group were more short term. The only significant effect of IBV infection on shell quality measurements was paler egg shells from the T-infected birds for the first 5 weeks post-infection.

'Mycoplasma synoviae' ('M. synoviae') can cause respiratory disease, synovitis, peritonitis, egg apical abnormalities or a subclinical infection. The importance of 'M. synoviae' is well established in broilers but only a few studies have been conducted in layers. In the present study, the prevalence of 'M. synoviae' in commercial layer flocks was determined by ELISA using egg yolk antibodies. Subsequently, a possible correlation between the serological status of 'M. synoviae' and egg shell quality was also studied. In the flocks under study, seroprevalence of 'M. synoviae' was found to be 69 % (95 % confidence interval (CI) = 47 to 91). Statistical analysis showed that the vaccinated group (3.0 ± 0.1) had the highest translucency score as compared to infected (2.4 ± 0.1) and uninfected (2.5 ± 0.1) groups, whereas % shell reflectivity was highest in the infected group (31.41 ± 0.3) as compared to the other two groups. Shell breaking strength (39.5 ± 0.5 Newtons) and shell deformation (298.7 ± 3.8 μm) values were significantly lower in the infected group than in the uninfected and vaccinated groups. There was no significant difference among these three groups for egg quality parameters egg weight, egg shell weight, % egg shell, shell thickness.

The horizontal infection of table eggs by food-poisoning causative agents such as 'Salmonella' is a serious concern for consumers and industry. While there are some factors that are associated with increased rates of infection the mechanism of bacterial entry remains unknown. The use of Computed Tomography (CT) enables the production of transverse images of the shell's interior. This imaging has allowed for identification of alternative pore structures, branching pores have been found, and both internally and externally branching pores are present in egg shells of laying hens. Using the agar egg penetration method first described by Board and Board (1967), the contents of 208 eggs were removed and the shells filled with molten XLD agar.

In Australia, currently, all pullets reared for egg production are vaccinated by live attenuated strains of infectious bronchitis virus. Various vaccines and protocols to control this viral disease have been developed, although the severity of the disease varies from place to place and flock to flock. In the present trial, effects of vaccine strains on the oviduct of laying hens were assessed by determining the presence and persistence of viral load following experimental infection. There was no drop in egg production in any of the groups. Both A3 and Vic S vaccine strains were detected in the oviduct of vaccinated and unvaccinated hens, mainly on the 12th day p.i. Both the vaccines appeared to be safe for the oviduct.

Egg shell translucency, which can be due to changes in the mammillary cores and mamillary layer during the early phases of eggshell formation, has the potential to increase the incidence of microcracks in egg shells, and hence, may facilitate bacterial penetration. There was a significant correlation between egg shell translucency and egg shell penetration by 'Salmonella' Infantis. 'Salmonella' Infantis was able to penetrate translucent egg shells even at very low doses. The penetration, however, appeared to be hindered in both translucent and non-translucent eggs at 4°C, as compared with room temperature which highlights the importance of storage of eggs at refrigeration temperatures.

This experiment was conducted to study the prevalence of 'Salmonella' and 'Escherichia coli' ('E. coli'). from the surface of egg shells, egg shell membranes or pores, and internal contents from unwashed eggs collected from commercial caged layer farms in Australia. Egg shell swabs, shell crush and egg internal contents (yolk and albumen) of an individual egg were processed for bacteriological examination. 'Salmonella' spp. were not detected from any of the egg shell surfaces, egg shell crush or egg internal contents. Thirty five 'E. coli' isolates were isolated from the egg shell surface. Ten 'E. coli' strains were also isolated from shell crush. However, the internal contents of eggs appeared to be sterile. Polymerase chain reaction was performed on forty-five 'E. coli' isolates using primers for heat stable enterotoxin genes A and B (STa and STb) and also for colicin V gene (cvaC). STa gene was detected in four 'E. coli' isolates isolated from egg shell surfaces. All the 'E. coli' isolates were negative for STb and cvaC genes. These data provide useful information regarding the prevalence of virulent 'E. coli' and 'Salmonella' spp. on and in unwashed eggs collected from layer farms. These data also suggest that unwashed eggs collected from caged layer farms are unlikely to be sources of 'Salmonella' outbreaks. Egg shell translucency could be due to changes in the mammillary layer and mamillary cores during the early phases of egg shell formation and has the potential to increase the incidence of microcracks in egg shells, and hence, may be responsible for bacterial penetration. There was a significant correlation between egg shell translucency and egg shell penetration by 'Salmonella' Infantis and 'E coli'. Both strains of bacteria were able to penetrate the translucent egg shells even at very low doses. The penetration, however, was hindered in both translucent and non translucent eggs at 4°C, as compared with room temperature which highlights the importance of storage of eggs at refrigerated temperatures.

The effect of two vaccine strains of infectious bronchitis virus (IBV - VicS and A3 strains) on internal and external quality of eggs was studied in Isa Brown hens in full lay. Birds were either unvaccinated for IBV or had been vaccinated during rearing. The main effects of exposure to the vaccine viruses were that VicS resulted in paler coloured shells, mainly in the unvaccinated birds and the eggs from the hens challenged with VicS were more elongate than the other groups. These findings are consistent with our earlier findings with field strains of IBV and differ from those reported in the literature for different strains of IBV.