Experiment 1 and Experiment 2: Exp. 1, two groups of Romanov ewes received single vaccinations s.c. by single injection with either 10⁵ Mic1-3KO tachyzoites or 10⁵ S48 tachyzoites. Exp. 2, two groups of Bizet ewes were vaccinated s.c. by single injection with either 10⁵ or 2 × 10⁶ Mic1-3KO tachyzoites. One group in each experiment was not vaccinated (control). All ewes were challenged per-os with 400 sporulated oocysts of the PRU strain at mid gestation. (A) Mean rectal ± S.D. temperature of groups and (B) systemic IgG against T. gondii measured by ELISA after vaccination (mean and S.D.), line indicates positive cut off point. (C) Mean ± S.D. rectal temperature following challenge.