Comparison of performance of dairy herds that did and did not vaccinate with a BHV1 marker vaccine in 1998

This study analysed the effects of the use of bovine herpesvirus 1 (BHV1) m arker vaccine on the performance of dairy cattle. In Spring of 1999, vaccin ation of 12 herds with the BHV1 marker vaccine resulted in severe animal he alth problems and mortality. The vaccines used on these farms were all from a batch that appeared to be contaminated with bovine virus diarrhoea virus type 2. This led to a general call to farmers and veterinary practitioners to report side-effects of this vaccine. As a result, more than 7000 farmer s reported symptoms. The information was obtained by means of a questionnai re; there was no control group. To determine the effects of the use of the marker vaccine, it was necessary to perform a study based on objectively ac quired information. The information collected by the Royal Dutch Cattle Syn dicate and the office of Identification and Registration was compiled into herd indices on production, udder health, reproduction, and culling. Two gr oups of dairy farms that had used the BHV1 marker vaccine (attenuated and i nactivated vaccine) were compared with farms that were certified BHV1-free. The analyses were performed based on intra-herd comparisons, meaning that per herd each index calculated over a certain period of time after the use of the marker vaccine was compared to a similar period of time prior to the use of the marker vaccine. A total of 144 comparisons were made. Seven com parisons were statistically significant. In two comparisons, the results we re in favour of the BHV1-free farms and in five comparisons, the result wer e in favour of the vaccinated farms. Thus use of the BHV1 marker vaccine co uld not be proven to affect herd performance. The sensitivity of the tests was very high, so with a high level of probability even very small differen ces in indices between groups would have been detected.