PSIV-12 Evaluation of reproductive performance and herd longevity when heifers grazing native range are vaccinated with a lifetime regimen of a killed viral or modified live viral vaccine

Abstract

Abstract Fifty-eight Angus × Hereford cross heifers born in the spring of 2015 were randomly assigned to treatments of receiving a modified-live viral (MLV) or killed viral (KV) vaccination against bovine viral diarrhea virus (BVDV) at 60-d of age to determine the effects of vaccination on fertility and herd longevity. Heifers received vaccine treatments again at weaning (205d) at re-vaccination, and a yearly booster for the duration of their time in the herd. Blood samples were collected every two weeks prior to breeding to assess puberty attainment and were subsequently subjected to ovarian ultrasonography to measure antral follicle counts (AFC) and reproductive tract score (RTS). Heifers were synchronized utilizing the 7-d CIDR-PG protocol with AI following estrus detection. Heifer AFC, uterine horn diameter, RTS, and proportion of females attaining puberty before the breeding season were similar among treatments (P ≥ 0.38). Artificial insemination pregnancy rates, final pregnancy rates, and percentage of heifers that calved in the first 21 days were similar between vaccination treatment groups (P ≥ 0.19). Body condition score through the third parity at calving and weaning were not different between vaccination types (P ≥ 0.59). Females receiving a MLV vaccination remain in the herd in a similar proportion to those receiving a KV vaccination (P = 0.86). These results indicate that different vaccination strategies can be successfully used in beef cattle grazing native range without impacting fertility, or herd longevity.