Effect of vaccination against bovine herpesvirus 1 with inactivated gE-negative marker vaccines on the health of dairy cattle herds.

The aim of this study was to estimate the effect of the bovine herpesvirus 1 (BHV-1) vaccination on herd health and production in BHV-1 infected Estonian dairy cattle herds. Seven herds vaccinated with inactivated gE-negative BHV-1 marker vaccines and seven matched non-vaccinated herds were selected. In vaccinated herds the calving interval was on average 7.01 days shorter compared to that in the non-vaccinated herds (coef=-7.01, 95% CI=-11.98, -2.03, p=0.008) during the study period (2007-2012). In non-vaccinated herds the insemination index had an increasing trend (coef(log scale)=0.03, 95% CI=-0.003, 0.06, p=0.054) and the first service conception rate decreased (coef=-2.19, 95% CI=-3.91, -0.47, p=0.015), whereas no significant changes occurred in vaccinated herds. Average yearly milk yield per cow increased (coef=145.30, 95% CI=-6.11, 296.71, p=0.065) and length of the dry period decreased in BHV-1 vaccinated herds (coef(log scale)=-0.02, 95% CI=-0.04, 0.004, p=0.056) compared to non-vaccinated herds during the study years. Youngstock and the cow culling rate due to respiratory disease was significantly lower in vaccinated herds compared to non-vaccinated herds (coef=-0.29, 95% CI=-0.47, -0.11, p=0.003 and coef=-0.15, 95% CI=-0.29, -0.007, p=0.043, respectively). These results suggest that vaccination against BHV-1 is associated with herd health and productivity.