The effect of T-strain infectious bronchitis virus on early lay pullets that had received different first vaccinations, and their third vaccination at either 14 or 18 weeks, was examined. For the whole flock there was an immediate decline in egg internal quality after challenge with the virus. Shell quality also declined as evidenced by both objective measurement and visual assessment. There were no major effects due to the strain of vaccine that the birds received at day old, although there were some effects of vaccine protocol. The revaccination of birds at 5% lay (18 weeks old) resulted in an increased decline in egg quality measurements when they were challenged with T-strain. This flock is continuing to be monitored to assess long-term effects.

Measurements of infectious bronchitis virus (IBV) antibody titres by IDEXX IBV antibody ELISA were compared with the results of agar-gel precipitation (AGP) and serum neutralisation (SN) tests. The percentage of samples testing positive by AGP and SN increased as the ELISA IBV antibody titre increased. Although it is not clear at what antibody titre level birds are protected against intercurrent infection, a mean IBV antibody titre measured by IDEXX ELISA of 439 correlated with a high level of protection against exposure to T-strain IBV. A comparison of two different IBV antibody ELISA kits showed a significant linear correlation although individual samples did not always correlate closely.

Different vaccination protocols with two vaccine strains (VicS and A3) for infectious bronchitis (IB) virus were administered to Isa Brown laying hens during rearing and half the birds were revaccinated regularly during lay. At 57 wks of age, half of the birds were placed into an induced moult for a period of 5 weeks (moulted prior to revaccination), all birds were then revaccinated for IB and the other half of the birds moulted (moulted following revaccination). Production was lower in the birds that were revaccinated regularly during lay and the control (no vaccination until 14 weeks) and VicS eyedrop groups. Egg shell quality was better in the birds that were revaccinated prior to moult. Excreta moisture following revaccination was higher in the birds that had been revaccinated regularly during lay and in birds that were moulted after revaccination.

Different vaccination protocols for infectious bronchitis virus (IBV) were administered to ISA Brown laying hens during rearing and half the birds were revaccinated regularly during lay. At 57 wks of age, half of the birds were placed into an induced moult (moulted prior to revaccination), all birds were then revaccinated for IB and the other half of the birds moulted (moulted following revaccination). Production and egg quality were lower in the birds that were revaccinated regularly during lay, especially from 18 to 56 weeks. IB antibody titres increased at 6 and 16 weeks, then decreased and remained relatively constant from 27 to 77 weeks, increasing markedly following exposure to T-strain IBV. Egg shell quality was better in the birds that were revaccinated prior to moult. There appears to be little advantage, and some disadvantage, of regular revaccination during lay, provided that the birds have been effectively vaccinated during rearing.

The eggshell quality of vaccinated hens challenged with infectious bronchitis (IB) virus in-lay at 41 weeks of age was found to decline. These effects were observed in hens vaccinated only during the growth phase and not revaccinated during the lay period. T strain virus was found to have a more prolonged impact while the antigenically-different Nl/88 strain produced a greater decrease in egg quality parameters. There was an unexpected increase in internal quality of the virus-exposed groups during the challenge period. While the genetic strain of the hen had no significant effects on the response to challenge in terms of egg quality, there were inherent strain differences in egg quality unrelated to the challenge and these are briefly discussed.