190 RELATIONSHIP BETWEEN BLUETONGUE VIRUS INFECTION AND FETAL MORTALITY IN CATTLE

Abstract

Infection by Bluetongue virus (BTV) may affect reproductive performance but little is known about its real impact on fertility and occurrence of abortions. The aim of this study was to describe the effects of BTV infection on fetal mortality in 53 herds located in the east of France that were infected by the virus between August and November 2007. In 2008, 2 visits were performed 50 days apart by local veterinary surgeons and pregnancy was checked by ultrasonography. The first visit aimed to record data on pregnancy and infection status and to register clinical signs. A total of 1939 cows were classified within 3 groups: nonpregnant (n = 262), early pregnant (<3 months, n = 1041), and late pregnant (>3 months, n = 636). For each cow, a blood sample was collected approximately 8 days after the first visit and BTV status was determined by ELISA. The rates of clinical symptoms and fetal losses were compared in seronegative and seropositive cows using chi-square tests. Bluetongue status was found positive in 69.5% of the cows (80% of beef v. 67% of dairy cows). Prevalence was highly variable between herds: 19% of herds had 100% of cows with positive serological results and 10 herds presented at least 70% of seronegative results. Clinical signs were reported by farmers in 40% (457/1141) of seropositive cows compared to 20% (90/460) of seronegative cows (P < 0.001). As a consequence, clinical signs should not be considered as a reliable tool for diagnosing BTV infection with enough accuracy. At first visit, ultrasonography was performed in cows that were supposed to be pregnant. At second visit, a positive pregnancy status was confirmed in 78% of the cows, but this proportion was higher in seronegative cows when compared with seropositive cows (81 v. 76%; P < 0.02). This proportion was associated with the presence of clinical signs. Out of 1311 pregnant cows at first visit, only 37 presented a fetal mortality at second pregnancy check (2.8%).The rate of fetal mortality was related to the BTV-seropositive status of cows as well as stage of pregnancy (P < 0.05; Table 1). Calving interval did not differ between seropositive and seronegative females (411 ± 77 days v. 405 ± 82 days; P > 0.10); however, number of AI per conception was significantly higher in seropositive than in seronegative females (2.0 ± 1.2 v. 1.8 ± 1.1; P < 0.001). These results show that a seropositive BTV status assessed by serological test (ELISA) is associated with an increased frequency of fetal mortality in beef and dairy cattle, and with an increased number of AI per conception.

Table 1.  Rate of fetal mortality observed between 2 pregnancy diagnosis 50 days apart (negative pregnancy check during the 2nd visit in cows which were pregnant at first visit)

The authors thank the farmers and veterinarians who participated to this trial, as well as the GDS (Groupements de Defense Sanitaire) organization from Moselle and Meuse departments for collecting the data.