The objectives of this study were to examine the serologic status of aborted dairy cattle with their fetuses against N.caninum infection. During two year, 151 blood and fetal fluid samples of aborted dairy cattle with their fetuses were collected from large dairy farms. The age of aborted fetuses ranged between 7 to 9 months. The maternal and fetal sera in every aborted case were examined by using ELISA method. N. caninum antibodies found in 38 (25 %) of dams sera and 23 (15%) of fetal sera of aborted dairy cattle. A significant association were observed between maternal and fetal sera status in cases of bovine abortion (P<0.0001). In this study , 19 (82.5%) of seropositive fetuses were aborted from seropositive dams and 4 (17.5%) of them from seronegative dams .Based on the serologic status of dam and their aborted fetuses against Neospora infection , t he rate of trans- placental transmission in infected cattle was calculated 50% (19/38). The range of OD ELlSA value in aborted dairy cattle and fetuses were 0.6- 2.7 and 0.28-1, respectively. There was not any significant association between the rate of OD values in seropositive dams and serostatus of aborted fetuses. The results indicate that the rate of trans-pelacental transmission of Neospora infection was high in large dairy farm in Mashhad area and had a significant association with abortion in the dairy farms

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