Trials with an enzyme-linked immunosorbent assay (ELISA) for the diagnosis of subclinical genital infections in rams caused by Histophilus ovis and Actinobacillus seminis

The performance of an enzyme-linked immunosorbent assay (ELISA) was evaluated in the serological diagnosis of subclinical genital infection in 6 naturally infected ram flocks and 2 experimentally infected ram hoggets. The test employs lipopolysaccharide (LPS) antigen prepared by autoclaving from Actinobacillus seminis and Histophilus ovis. A total of 193 sheep (118 unmated virgin rams and 75 mature breeding rams) were examined clinically, serologically (by ELISA) and bacteriologically (semen bacteriology) at the same time. Serum samples from all animals were also tested by an ELISA employing LPS antigen prepared from Brucella ovis in the same way. Shedding of A. seminis and H. ovis did not show close correlation with serological positivity (Table 1), as only 9 (15.0%) out of the 60 A. seminis shedders were ELISA seropositive at the same time. As regards H. ovis only 10 (19.2%) out of the 52 H. ovis shedders were ELISA seropositive at the same time. The results indicate that, when used alone, the ELISA employing LPS antigen is unsuitable for diagnosing subclinical genital infection caused by H. ovis and A. seminis in rams. The authors discussed shortly the employing fields of this ELISA test in the diagnostic work.