Abstract Neospora caninum is an apicomplexan protozoon causing abortion in cattle worldwide. The present study was designed to assess the importance of this parasite for causing abortion in dairy farms in the Mashhad area of Iran. Of the aborted bovine fetuses, 151 were collected from dairy farms between 2006 and 2008. First, brain samples were examined by polymerase chain reaction (PCR) for the presence of N. caninum DNA, diagnosis was complemented with immunohistochemistry (IHC) and fetal serology (ELISA). Twenty-two (14.5%) of bovine fetuses were considered to be infected with N. caninum with at least one diagnostic technique being positive. PCR yielded 18 (11.9%) positive out of 151 brain samples. Only 52 brain samples were suitable for IHC examination, and N. caninum organism was detected in six (11.5%) of these 52 brain samples. Fetal fluids (n=151) were assessed with a N. caninum-ELISA, resulting in 15 (9.9%) seropositive fetal fluids samples. In the present study, a good agreement was observed between PCR and ELISA, and a fair agreement between PCR and IHC. The results indicatedthat abortion due to N. caninum infection is prevalent among large-size dairy farms in the Mashhad area of Iran,mnand that different complementary diagnostic techniques should be used to increase the chance to detect N. caninum

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