Prevaccination bovine viral diarrhea virus titers and subsequent reproductive performance in dairy heifers.

The study was conducted to determine if there was a relationship between prevaccination bovine viral diarrhea virus (BVDV) titers in 14 month-old dairy heifers and time open during first lactation, length of the conception interval, fetal survival during the second pregnancy, and age at culling. Possible associations were analyzed using nonparametric survival methods and survival distributions were described using the product-limit (Kaplan Meier) methods. Regression analysis was used to estimate the correlation between pre- and postvaccination BVDV titers three years after vaccination. Evidence of exposure to BVDV prior to 14 months of age was demonstrated by serum-virus-neutralization titers greater than 1:4 for 97% and greater than or equal to 1:128 for 67% of the 72 heifers followed. No correlation was found for 38 pairs of prevaccination and postvaccination titers (p = 0.76). The risk of being culled was high for heifers (n = 41) with very low (1:2-1:8) or very high (> or = 1:256) titers, but low for heifers (n = 31) with moderate (1:16-1:128) prevaccination titers (p = 0.098). Risk of subsequent fetal loss was high for heifers (n = 30) with very low (1:2-1:16) or very high (> or = 1:256) prevaccination titers, compared to heifers (n = 24) with moderate (1:32-1:128) titers (p = 0.084). These findings suggest that prevaccination exposure to BVDV eliciting either a very weak or a very strong serological response may contribute to subsequent reproductive inefficiency and an increased risk of culling.