Preliminary studies on the effects of infectious bronchitis on unvaccinated laying hens

Preliminary studies were conducted on unvaccinated laying hens to investigate the effects of two strains of infectious bronchitis virus (T strain and N 1/88 strain) on unprotected birds during lay. Clinical symptoms associated with the respiratory system were observed in the T-strain and N-strain groups but not the control and some birds in the T-strain group had enlarged kidneys. Feed intake tended to be depressed in the challenged birds and production was reduced in the T-strain group at 3 weeks post-challenge. However, there were relatively few effects of challenge on egg quality and no significant effects on excreta moisture. IBY antibody titres increased in response to challenge in the T-strain group but only some challenged birds produced antibodies in the N-strain group. Virus was re-isolated from the kidneys of T-strain birds at all sampling times post-challenge but only at 6-16 days for the N-strain group. Further studies are planned to document the effect of IBY challenge on unvaccinated birds.