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

Abstract: 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 days pre-breeding, before initiation of a 7-day CIDR-PG timed artificial insemination (TAI) protocol. Ten days following TAI cows were exposed to herd bulls for 60 days. Pregnancy assessment occurred 30 and 100 days 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 days prior to breeding in beef herds with previous use of modified-live virus vaccines.