The agar?gel precipitin response to the H120 and H52 vaccines of infectious bronchitis virus

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Abstract
The respiratory and agar‐gel precipitin response of chickens to H120 and H 52 vaccines of infectious bronchitis virus (IBV) were studied. On aerosol exposure of 3‐weeks‐old chicks to H120, slight respiratory symptoms were observed in 30% while 70% produced precipitins. Eleven‐weeks‐old chicks inoculated intratracheally with H52 alone showed severe symptoms and 100% produced precipitins. Similar birds previously vaccinated with H120 showed no symptoms on challenge with H52 but 55% produced precipitins. Although this may preclude the use of the test in some outbreaks of IB, it could be applied, at appropriate times, to replacement laying stock and perhaps in the investigation of the “egg‐drop syndrome”.