Quantification of protoporphyrin IX from eggshell of brown egg laying hens challenged with vaccine and wild strains of infectious bronchitis virus

Abstract

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.