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 temperature-sensitive modified-live bovine herpesvirus type-1 (BHV-1) vaccine against BHV-1 challenge-induced abortion and stillbirth.

DESIGN

Prospective 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 vaccinate (n = 10) or nonvaccinate control (n = 10) group. Seventeen to 26 days after members of the vaccinate group received a second dose of vaccine, all heifers were artificially inseminated. Heifers were challenged intravenously with Cooper strain BHV-1 between days 177 and 187 of gestation. Aborted fetuses and stillborn calves were necropsied, and tissues collected for histologic examination and virus isolation. Heifers, calves, and fetuses were tested for BHV-1 antibody throughout the study.

RESULTS

The difference in number of abortions or stillbirths between vaccinated heifers (1/10) and control heifers (10/10) was significant (P < 0.003). Seven of 10 control heifers had a virus neutralization antibody 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 replacement heifers with modified-live BHV-1 vaccine provides fetal protection at 6 months of gestation (7 months after vaccination) and appears to be a reasonable precaution to control economic losses associated with BHV-1 infection. Abortions induced by BHV-1 are not necessarily associated with rising or markedly high virus neutralization antibody titers. These titers should be used cautiously when assessing the role of BHV-1 in bovine abortion and stillbirth.