Evaluation of abortions in cattle attributable to neosporosis in selected dairy herds in California.

OBJECTIVE

To estimate the minimum rate of abortion attributable to infection with Neospora sp in selected California dairy herds.

DESIGN

Prospective study.

ANIMALS

Twenty-six dairy herds containing 19,708 cows were studied. Fourteen herds had a history of abortions attributable to neosporosis, and 12 were herds in which neosporosis had not been identified as a cause of abortions.

PROCEDURE

During a 1-year period, all available aborted fetuses were submitted to veterinary diagnostic laboratories to determine the cause of abortion. Reproductive records of cows that aborted were reviewed.

RESULTS

Neospora sp infection was the major cause of abortion identified (113/266 abortions, 42.5%). The majority (232/266, 87.2%) of the aborted fetuses were submitted from herds with a history of abortions attributable to neosporosis, and Neospora sp infection was identified as the causative agent in 101 of 232 (43.5%) of the abortions from these herds. Fewer aborted fetuses were submitted from the 12 herds that did not have a history of abortion attributable to Neospora sp; however, neosporosis was confirmed as a cause of abortion in 6 of these 12 herds and was identified as the causative agent in 12 of 34 (35.3%) abortions from these herds. The disease was widespread throughout the state (19/26 herds in our study). Available reproductive histories of cows that had abortions attributed to neosporosis were evaluated, and 4 cows were identified that twice aborted Neospora-infected fetuses.

CLINICAL IMPLICATIONS

Abortion attributable to Neospora sp infections can be expected to be a continuing major cause of abortion in dairy herds with a history of neosporosis as well as in dairy herds that have a history of sporadic abortions, but for which Neospora sp infections have not been previously identified as a cause of abortion. Subsequent pregnancies in cows that abort a Neospora sp-infected fetus also are at risk of infection, suggesting that the immunity provided by an initial infection is inadequate to prevent repeat infection or that cows can be persistently infected with Neospora sp.