Influence of Vaccination with an Inactivated or Modified Live Viral Reproductive Vaccine on Reproductive Parameters in Beef Cows

Abstract Text: A two year study involving nine herds of well-vaccinated cows and heifers (n = 1436) was conducted to evaluate whether a pre-breeding MLV or inactivated reproductive vaccine administered per label instructions had negative impacts on conception rates or calving distribution compared to a non-vaccinated control (saline) group.   Within herd, cows were blocked by parity and calving date and randomly assigned to receive one of the two treatments (MLV or Inactivated) or saline (Control).  All females were synchronized with the 7-d CO-Synch + CIDR protocol and inseminated (AI) at the appropriate time after CIDR removal (cows 60 to 66 hrs; heifers 52 to 56 hrs).  Cows remained separated from bulls for at least 10 d after AI.  Pregnancy success and fetal age were determined on d 28 after AI, and > 30 after the breeding season.  Data were analyzed using the GLIMMIX procedure in SAS with herd as a random variable.  Days postpartum influenced conception rates with heifers and short postpartum cows having decreased conception rates compared to cows that were further postpartum (P < 0.05).  There was no difference in conception rates to AI between MLV and Control groups (P = 0.21; 40.0 ± 4% vs 43.3 ± 4%) or between Inactivated and Control groups (P = 0.49; 46.5 ± 4% vs 43.3 ± 4%).  Rates tended to differ between MLV and Inactivated groups (P = 0.055).    At 56 d after AI, MLV animals (88.9 ± 2%) had decreased pregnancy success compared to both the Inactivated (93.2 ± 2%) and Control groups (92.5 ± 2%, P ≤ 0.01).  Breeding season pregnancy success was similar between MLV and Control groups (P = 0.34; 95.2 ± 2% vs 96.4 ± 1%) as well as between the Inactivated and Control groups (P = 0.14; 98.0 ± 1% vs 96.4 ± 1%).   Inactivated and MLV vaccine groups were different (98.0 ± 1% vs 95.2 ± 2%; P = 0.01).  When cumulative calving distribution was evaluated, the proportion of females that calved by d 12 and 30 of the calving season were similar between MLV vaccine and Control groups (P > 0.30) and between the Inactivated and Control groups (P > 0.30).    However, Inactivated tended (P= 0.09) to be greater compared to MLV.  In summary, treatment of well-vaccinated beef cows and heifers with a MLV or inactivated reproductive vaccine 30 d pre-breeding resulted in similar pregnancy rates and calving distributions as non-vaccinated Controls.

Keywords: Modified-live, Inactivated, Vaccine, Reproductive success