Relationship between Toxoplasma gondii seroprevalence and lamb marking in South Australian sheep flocks.

Overall, 209 of 875 (23.9%; 95% confidence interval [CI] 16.3% to 31.4%) of individual ewes tested seropositive for T. gondii-specific IgG antibodies, with a flock level seroprevalence of 28/29 (96.6%, 95% CI 96.6% to 100%). On individual farms, the seroprevalence ranged from 0% to 93.3%. Analysis showed that Kangaroo Island properties had significantly higher mean seroprevalence than any mainland climatic regions, and that the mainland regions did not significantly differ from each other. Linear regression revealed a significant association between seroprevalence and lamb marking percentage, with a slope of -5.4% lamb marking per +10% seroprevalence.