Immunity to Escherichia coli in Pigs: Serologic Response of Sows Given Formalin-Treated Live Escherichia coli Vaccine

SUMMARY Vaccination of sows with a formolized, live Escherichia coli vaccine resulted in inhibition of natural serum bactericidal activity in sows vaccinated by the intramammary route. The bactericidal activity was replaced with what has been termed immune serum bacteriostasis. The development of immune serum bacteriostasis was more marked in sows given the vaccine by the intramammary route than in those intramuscularly vaccinated. The bacteriostatic factor was not complement dependent, was heat stable, and was not specific to the vaccinal strain. Indirect hemagglutination titers were higher in the serum of sows vaccinated via the intramammary route than in those vaccinated by the intramuscular route.