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.

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.

Different vaccination protocols for infectious bronchitis (IB) virus were administered to Isa Brown laying hens. Half the birds were revaccinated regularly during lay whereas the other birds were not vaccinated beyond 14 weeks of age. Body weight, production, blood haematocrit and plasma electrolyte concentrations were not affected by vaccination treatment. However, egg and egg shell quality differed between birds which were revaccinated regularly and those which were not. In general, egg shell quality was better in the birds which were not revaccinated at regular intervals. The birds which were vaccinated initially with the A3 vaccine tended to have lower albumen height and Haugh Units than the other treatment groups. The IB antibody titres were greatest at 6 and 16 weeks for both revaccinated and non-revaccinated birds. However, regular revaccination of birds beyond 14 weeks of age had no significant effect on IB antibody titre levels. These results suggest that there may be no advantage in regular vaccination of birds for IB, provided that birds have been properly vaccinated during rearing. However, more information is required about the correlation between blood IB titre levels and protection against intercurrent IB infection before recommendations can be made to the Australian industry.

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.

Diets based on wheat, barley or sorghum were fed to younger and older laying hens for a period of 12 weeks. Production and weekly egg mass were higher for the younger birds and feed intake and feed conversion efficiency were higher for the older hens, with no effect of diet. Egg shell quality and egg internal quality were better for the younger hens. The sorghum diet resulted in eggs with better shell quality but lighter shell colour and lower albumen quality. AME was higher for the older birds and differed among diets, with sorghum the highest and barley the lowest. Excreta moisture was higher for the wheat and barley diets than the sorghum diet, and higher for the older birds. The digesta viscosities of the jejunum and ileum were higher for the wheat and barley diets than for the sorghum diet and not different between the younger and older hens.

Egg shell quality and egg internal quality are of major importance to the egg industry worldwide. This review covers the formation of the hen's egg and ways of measuring egg shell quality and egg internal quality. Egg shell quality may be measured as egg size, egg specific gravity, shell colour, shell breaking strength, shell deformation (destructive or non-destructive), shell weight, percentage shell, shell thickness, and shell ultrastructure. New methods emerge from time to time. Egg internal quality is measured as yolk colour, the integrity of the perivitelline membrane, and albumen quality. Factors that affect egg shell quality and egg internal quality are reviewed. The complexity of the process of egg shell formation means that imperfections can arise in a number of places in the oviduct of the hen. Egg shell quality may be affected by the strain and age of hen; induced moult; nutritional factors such as calcium, phosphorus, vitamins, water quality, non-starch polysaccharides, enzymes, contamination of feed; general stress and heat stress; disease, production system, or addition of proprietary products to the diets. Egg internal quality may be affected by storage; hen strain and age; induced moult, nutrition, and disease. An understanding of the range of factors that affect egg shell quality and egg internal quality is essential for the production of eggs of high quality.

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.

Histological examination was conducted of kidneys made available from a previous experiment, which investigated different infectious bronchitis virus (IBV) vaccination protocols for laying hens (Sulaiman et al., 2001). Histological changes were used as a possible measure of the level of protection afforded by different vaccination protocols. Kidneys were examined from ISA Brown cockerels that were vaccinated at day old or two weeks by coarse spray, eye-drop or drinking water and then revaccinated by the same routes at 8 weeks. A control group of unvaccinated birds was also maintained. Ten birds from each group were challenged at 11 weeks of age with T-strain infectious bronchitis virus. Five birds from each group were euthanased at one, two and three weeks post exposure and the kidneys preserved for histological examination. At each time interval following exposure to T-strain IBV, kidney sections were prepared from the birds with the largest and smallest kidneys (as a percentage of body weight), stained with haematoxylin and eosin, and examined for histological changes (a total of 6 birds per treatment, 2 kidneys per bird, 3 divisions per kidney). Also, the cranial divisions were examined for all 5 birds in vaccinated groups that showed histopathology.

Infectious bronchitis (IB) is often associated with declines in egg production and eggquality. Deterioration in internal quality is the most commonly mentioned negative effect ofvirulent IB infection. At present all commercial laying pullets are vaccinated with liveattenuated vaccines. The strain of vaccine used, timing of exposure and number ofexposures vary among producers. Revaccination with live attenuated vaccines during lay canproduce deleterious effects on egg production and quality. The trial described in thispresentation was one in a series, investigating if rearing phase vaccination can adequatelyprotect laying hens against virulent IB impacts on egg production and quality throughout thelay cycle.Egg production and egg quality response to challenge at 62 weeks with T-strain IBVwas evaluated in 320 vaccinated birds. The birds were vaccinated at 4, 28 and 198 days withone of A3 (A) or VicS (V) vaccine strains to form four vaccination treatment groups AAA, AVA,VVV and VAV. Egg production declined significantly for three weeks post-exposure to T-strainIBV. Moderate negative effects were found of IBV on shell quality measurements, but nodeleterious effects were found on internal quality measurements. All birds were still partiallyimmune to some of the egg quality effects of T-strain IBV when challenged late in lay.