Abstract
Efficacy of infectious laryngotracheitis (ILT) live virus vaccine was determined in combination with Newcastle disease (ND) or infectious bronchitis (IB) live virus vaccine by ocular administration to chickens. As for the ILT and IB vaccines, the efficacy of each vaccine was not altered even if both vaccines were inoculated simultaneously. On the contrary, when ILT vaccine was administered simultaneously or contiguously with ND vaccine to young chickens, the marked suppression was observed in ILT immunization. Significant immunosuppression occurred when ILT vaccine was inoculated during the period between 3 days before and 5 days after vaccination with ND vaccine in chickens younger than 5 weeks of age. It did not occur, however, in chickens older than 7 weeks of age or having antibody against ND virus enough to protect growth of the ND virus. These facts show that careful attention must be paid when ILT and ND live virus vaccines are administered to young chickens.
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