EFFICACY OF A TEMPERATURE-SENSITIVE MODIFIED-LIVE BOVINE HERPESVIRUS TYPE-1 VACCINE AGAINST ABORTION AND STILLBIRTH IN PREGNANT HEIFERS

Objective-To evaluate the efficacy of a commercially available tempera ture-sensitive modified-live bovine her pesvirus type-1 (BHV-1) vaccin e against BHV-1 challenge-induced abortion and stillbirth. Design-Pros pective randomized control trial. Animals-20 cycling, nonpregnant, BHV -1 seronegative heifers of various breeds and weights, 12 to 15 months old. Procedure-Heifers were randomly assigned to a vac cinate (n = 10 ) or nonvaccinate control (n = 10) group. Seventeen td 26 days after m embers of the vaccinate group received a second dose oi vaccine, all h eifers were artificially inseminated. Heifers were challenged intraven ously with Cooper strain BHV-1 between days 177 and 187 of gestation. Aborted fetuses and stillborn calves were necropsied, and tissues coll ected for histologic examination and virus isolation. Heifers, calves, and fetuses were tested for BHV-1 antibody throughout the study. Resu lts-The difference in number of abortions or still-births between vacc inated heifers (1/10) and control heifers (10/10) was significant (P < 0.003). Seven of 10 control heifers had a virus neutralization antibo dy titer to BHV-1 at abortion or stillbirth that declined or remained unchanged from their titer at a previous serologic evaluation (7 to 66 days earlier). Clinical Implications-Prebreeding vaccination of repla cement heifers with modified-live BHV-1 vaccine provides fetal protect ion at 6 months of gestation (7 months after vaccination) and appears to be a reasonable precaution to control economic losses associated wi th BHV-1 infection-Abortions induced by BHV-1 are not necessarily asso ciated with rising or markedly high virus neutralization antibody tite rs. These titers should be used cautiously when assessing the role of BHV-1 in bovine abortion and stillbirth.