SECULAR AND SEASONAL TRENDS OF NEOSPORA ABORTION IN CALIFORNIA DAIRY-COWS

This study was undertaken to determine if the proportion of dairy cow abortions attributable to Neospora sp. infection increased or occurred in a seasonal cycle during a 6-yr period. Abortions caused by Neospor a sp. were tallied for all fetuses submitted to the Tulare branch of t he California Veterinary Diagnostic Laboratory between January 1985 an d December 1990. Regression analysis of 221 cases of Neospora among 76 2 fetuses submitted showed a weak increasing secular trend (P=0.053, r (2)=0.05), with predicted monthly proportions at the beginning and end of the 6 yr of 0.16 and 0.33, respectively. Using a Kolmogorov-Smirno v-type statistic, comparison of the 12-mo distribution of Neospora sp. cases and a hypothetical distribution of cows at risk of aborting fou nd about 16% of variation in cases was attributable to season (P<0.01) . More cases were found in winter than in summer and early fall. Resul ts indicate that Neospora sp. abortion in California dairy cows is not new or recently emerging and that seasonally related factors influenc e some of the risk of abortion. Results suggest that Neospora sp. has contributed to the high dairy cow abortion rate for many years, and th at seasonally varying exposures may predispose to transmission or recr udescence of infection.