Passive immunisation of chicks against Escherichia coli.

At hatching, the level of maternal antibody to E. coli in chicks, measured by ELISA was found to be 55 to 62% of that of the hen. It declined to an undetected level at 21 days of age. A sonicated experimental vaccine when given with a Freund's complete adjuvant to breeder hens produced the highest antibody titres and which were maintained for at least 160 days (end of the experiment) as well as providing the progeny protection. Progeny of hens with high antibody titre challenged with the homologous bacteria at 7 and 14 days of age exhibited total resistance, while those challenged at 21, 34 and 45 days of age, when antibody titres were undetectable, still showed 30 to 40% higher resistance than the control group. The results indicated a correlation between the hen's antibody titre and percentage of survival of her progeny. Challenged progeny with a heterologous strain exhibited no protection. Hens which were vaccinated with a bivalent vaccine gave rise to chicks which were protected against both serotypes.