SEROPREVALENCE TO LEPTOSPIRA-INTERROGANS SEROVAR HARDJO IN MERINO STUD RAMS IN SOUTH-AUSTRALIA

A serological survey of 2160 Merino stud rams on 36 farms detected pos itive reactions greater than or equal to 1/100 in 42% of animals using the microscopic agglutination test (MAT) to Leptospira interrogans se rovar hardjo. Twenty flocks had seroprevalence values greater than 30% with 15 flocks having values greater-than-or-equal-to 60%. The enzyme -linked immunosorbent assays showed that 47% and 3% of rams on the 36 farms were positive for IgG and IgM antibodies, respectively. Forty-fi ve percent of hardjo reactions were in rams that had not been exposed to cattle. Significant correlations were found between IgM reactors an d creek/dam water pumped into troughs, and between MAT/IgG reactors an d total flock size. No statistical relationships were detected between positive reactors and two different annual average rainfall gradients , the time of the year in which samples were obtained, or agricultural regions of South Australia. Infections with an organism of the Sejroe serogroup is widespread in Merino stud rams.