Neosporosis is a disease caused by the protozoan Neospora caninum and its only clinical symptom in adult cows is abortion. In order to determine whether N. caninum was associated with an outbreak of abortion on a high milk production dairy farm with excellent livestock and health control standards, blood was collected from all the animals in the herd to obtain their serum and perform indirect ELISA. To this end, we followed the procedures of the HerdChek anti-Neospora caninum test kit to obtain

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... epidemiological information about isolated estrus repetition, production, recurrent estrus, isolated abortion and recurrent abortion on the dairy farm. Relative risk and Odds ratio were calculated and all the calculations were performed using SAEG 9.1 software. Of the 111 blood samples collected, 42% tested seropositive and among the 58 lactating cows, 16 (28%) were seropositive. High milk producing cows were more vulnerable to infection by N. caninum getting to have 4.5 lower risk of infection than lower milk producing cows. It was also observed that low milk productivity is associated with protection factor. No association was observed between isolate estrus repetition and seropositive and seronegative animals as well as between the presence of recurrent estrus and positive and negative cows. Significant association was observed between isolated abortion and seropositive and seronegative animals as well as between recurrent abortion and positive and negative animals evaluated. Therefore, we conclude that neosporosis does not interfere in fertility, but this is related strictly to abortions in the herd and this problem is most evident in high milk producing dairy cows.