Effect of IBV vaccination strain during rearing on egg production and quality following challenge with IB virus in the laying cycle

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.