Clinical evaluation of a commercial vaccine against chlamydial abortion of ewes.

The immunity of ewes vaccinated prior to breeding with an adjuvant vaccine prepared from yolk sac propagated chlamydiae, was challenged at 70 days of pregnancy by intravenous (IV) or intradermal (ID) inoculation of a suspension of virulent yolk sac propagated chlamydiae. The response to challenge inoculation was followed by recording rectal temperature, CF antibody titer, lambing performance and by chlamydial isolation from vaginal swabs. That vaccine did not protect against IV challenge: 7 of 10 vaccinated ewes, and 7 of 8 controls aborted. When the challenge was given by the ID route, the incidence of abortion was reduced: 4 of 9 vaccinated, and 9 of 9 control ewes aborted, but chlamydiae were isolated from vaginal swabs of 7 of the 9 vaccinated ewes.