Abstract
Bovine herpesvirus type 1 (BHV-1) is a major cause of reproductive failure. A study was conducted to determine if vaccination with a modified-live virus (MLV) vaccine containing BHV-1 at either 8 or 13 months prior to challenge protects against BHV-1 challenge-induced abortion. A total of 51 beef heifers, seronegative to bovine viral diarrhea virus types 1 and 2 and BHV-1, were vaccinated subcutaneously with a commercially available combination MLV vaccine containing BHV-1 and inactivated bacterin vaccine, or placebo containing bacterin only. The estrus cycle was synchronized and heifers wereartificially inseminated approximately 6 or 1 month(s) after vaccination. Heifers were challenge-inoculated intravenously at approximately 193 days of gestation with a virulent BHV-1 virus. Clinical signs of BHV-1 infection were monitored for 14 days following challenge. Serological status and occurrence of abortion or stillbirth were also determined. Tissues collected from aborted fetuses (n = 22) and full-term calves that were born dead (i.e., stillbirth [n = 1] or dystocia [n = 2]) were tested for BHV-1 via virus isolation. BHV-1 was isolated from 1 fetus (7.7%) from Treatment Group 1 heifers (TGl -heifers challenged 13 months after BHV-1 MLV vaccination), from 3 fetuses/calves (15.8%) from Treatment Group 2 heifers (TG2 - heifers challenged 8 months after BHV-1 MLV v~ccination), and from 7 fetuses (36.8%) from Treatment Group 3 heifers (TG3 - control heifers that rec~ived bacterin only). Polymerase chain reaction testing results indicated that 1 fetus from the 13 (7. 7%) TG 1 heifers, 5 fetuses out of the 19 (26.3%) TG2 heifers, and 18 fetuses out of the 19 (94.7%) TG3 control heifers were BHV-1 positive. In this study, a combination MLV vaccine containing BHV-1 administered 8 or 13 months prior to challenge provided a significant level of protection against fetal infection in the face of a substantial challenge infection with BHV-1 when compared to nonvaccinated controls.
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