[Oestrus suppression in a dairy herd by means of anti-GnRH vaccination Improvac®: A prospective field study].

The aim of this study was to evaluate the duration of estrus suppression after a double administration of the anti-GnRH vaccine Improvac® (Zoetis Schweiz GmbH, 2800 Delémont) in cows. Furthermore, it should be investigated, if a third administration could prolong the effect of the cycle suppression. A total of 21 cows (more than four weeks post partum) were vaccinated twice, at least 35 days apart, with 2 ml Improvac® (0.4 mg of a GnRH-analogon) subcutaneously on one side of the neck. Over a period of 368 days and in the course of 18 farm visits these cows were examined gynecologically and re-vaccinated if they showed signs of estrus behaviour or ovarian activity. After the second vaccination the cycle of the cows was suppressed for an average period of 114 days (59-175 days) and the effect could be prolonged by a booster of the vaccine for another 127 days in three cows. Estrus behaviour was absent for a longer period than ovarian activity was. The vaccine was tolerated well: apart from slight swelling at the injection site, no side effects were observed. Our results demonstrate that two immunizations with Improvac® are an easily applicable method for the suppression of cyclic activity in cows for a mean period of 114 days. The duration of cycle suppression was prolonged by a booster of the vaccination.