PSIII-8 The Effect of Pre-Breeding Vaccination with Modified-Live Virus or Inactivated Virus Vaccine on Body Condition and Reproductive Performance in Beef Cows

The objective of this study was to evaluate the effect of modified-live virus or inactivated virus vaccines on beef cow performance characteristics. Modified-live virus vaccines have broader immune system stimulation and longer effective duration than inactivated virus vaccines. The subsequent impact on cow performance, particularly reproduction, in well-managed herds is not well understood. Primiparous and multiparous cows (n = 877), from 3 herds, were stratified by age, body condition score (BCS), and body weight (BW) and randomly assigned to 1 of 2 treatments; 1) modified-live virus (MLV, 2-mL of Bovi-Shield GOLD FP 5 L5) and 2) inactivated virus (IV, 5-mL of CattleMaster GOLD FP 5 L5). Single dose vaccine administration occurred 42 d pre-breeding, before initiation of a 7-d CIDR-PG timed artificial insemination (TAI) protocol. Ten days following TAI cows were exposed to herd bulls for 60 d. Pregnancy assessment occurred 30 and 100 d post-breeding by rectal ultrasound. Cow BW and BCS were analyzed using PROC MIXED while reproductive performance variables were analyzed using PROC GLIMMIX of SAS 9.4. There were no differences (P ≥ 0.48) observed in BW or BCS at AI, pregnancy assessment 1, or pregnancy assessment 2 between cows receiving MLV or IV vaccine. No differences (P = 0.55) were observed in TAI pregnancy rate between cows receiving MLV or IV (66 versus 63%, respectively). Overall pregnancy rate did not differ (P = 0.71) between MLV (89%) and IV (90%) vaccines. Additionally, pregnancy loss from pregnancy assessment 1 to pregnancy assessment 2 was not different (P = 0.55) between MLV and IV. In this experiment, pre-breeding vaccine type did not impact cow BW, BCS, or reproductive performance. Overall, these results indicate that either MLV or IV vaccines can be utilized 42 d prior to breeding in beef herds with previous use of modified-live virus vaccines.