Immunity levels against avian encephalomyelitis in vaccinated poultry breeder flocks in Maine.

Four commercial poultry breeder flocks that were vaccinated under field conditions against avian encephalomyelitis (AE) with commercial live or inactivated vaccine were monitored periodically by virus-neutralization testing of blood serum samples and by challenge of their progeny eggs and chicks. The history of the flocks and results of the tests indicate that field exposure might occur during the laying period, thereby boosting immunity titers without causing clinical AE in the progeny chicks. The data also indicate field exposure of certain flocks before AE vaccination.