Toxoplasmosis in sheep I. Effect of a killed vaccine on lambing losses caused by experimental challenge withToxoplasma gondii

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Abstract
A total of 50 two-tooth ewes were immunized pre-tupping using a killed vaccine of disintegrated Toxoplasma tachyzoites with Freunds incomplete adjuvant. At mid-pregnancy, the ewes were challenged intravenously with 1×104 live T. gondii tachyzoites. There was no difference in the lambing percentage between ewes vaccinated once and unvaccinated ewes. The lambing percentage for ewes vaccinated twice was significantly lower (pToxoplasma dye test. The level of dye test antibodies at the time of challenge suggests that effective immunity to Toxoplasma abortion is not dependent on dye test antibody titre. These results suggest that a killed vaccine would not be an effective tool to estimate the effects of Toxoplasma on fertility and lambing performance in commercial flocks.