Infectious bronchitis virus and brown shell colour: Australian strains of infectious bronchitit virus affect brown eggshell colour in commercial laying hens differently

The aim of the current study was to assess any effect of wild and vaccine Australian infectious bronchitis virus (IBV) strains on shell colour in brown-shelled eggs. In Experiment 1, eggs were collected from day 1 to day 13 post-inoculation (p.i.) from unvaccinated laying hens challenged with IBV wild strains T and N1/88 and from a negative control group of hens. In Experiment 2, eggs were collected from 2 to 22 days p.i. from unvaccinated and vaccinated laying hens challenged with either a wild or a vaccine strain of IBV. In Experiment 1, there was a significant effect (P < 0.05) of day p.i. and of viral strain on shell reflectivity, L* and protoporphyrin IX (PP IX) in eggshells, with and without cuticle. The mean PP IX/g of shell with and without cuticle was significantly higher on day 1 p.i. compared to day 7, after which PP IX increased with day p.i. In Experiment 2, shell reflectivity and L* increased and PP IX decreased with increased day p.i. until day 12. Shell reflectivity and L* decreased slightly after day 12 and increased again towards day 22. Shell reflectivity, L* and PP IX were not significantly different for eggshells from unvaccinated and vaccinated laying hens in the intact eggshell, but were significantly different in shells from which cuticle had been removed. In conclusion, the IBV strains reduced the intensity of brown shell colour to different extents with a lower amount of PP IX in eggshells.