Associations between Neospora caninum infection and the reproductive performance of dairy heifers in their first and second pregnancy on 18 UK farms were examined. Six-month-old heifer calves were tested for N caninum-specific antibodies with a commercial ELISA, and were then monitored until their second calving. Random-effects regression analyses were performed on the data, using serological status as the explanatory variable. Of 460 heifers tested, 7.2 per cent were seropositive. Seropositive heifers were more likely to suffer gestational loss (late embryonic/early fetal loss and abortion) than seronegative heifers during their first (odds ratio [OR] 5.3, P<0.01) and second (OR 6.0, P<0.001) pregnancy. Seropositive heifers were also four times more likely to experience perinatal mortality (calf born dead or dying within 24 hours of parturition) at first (OR 3.9, P<0.01) and second (OR 4.5, P<0.1) calving. No significant association between seropositivity and the fertility parameters (age at first breeding and calving, days from calving to first service and conception, services per conception and calving interval) or conception failure was found. The results suggest that N caninum infection before pregnancy is a significant contributing factor to gestational loss and perinatal death, and thus serological screening of potential replacement heifers is recommended.
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