Effect on milk production of vaccination with a bovine herpesvirus 1 gene-deleted vaccine.

A field trial was conducted to determine the effect of vaccination with an inactivated bovine herpesvirus 1 (BHV1) gE-negative marker vaccine on the milk production of dairy cows. The daily milk yield of 455 cows in six herds was measured electronically from six days before vaccination until 14 days after vaccination. The treatment consisted of two injections with either vaccine or placebo, both at an interval of four weeks. There was a small, but significant (P < 0.05), decrease of about 1.4 litres per cow in milk production after a double vaccination, the negative effect being slightly greater after the second vaccination.