Induction of ovulation with GnRH or oestradiol benzoate lowers plasma progesterone concentration within the first week of ovulation in non-lactating Holstein cows

Abstract

Oestrous synchronisation involves synchronisation of ovarian follicular turnover, new wave emergence, and finally induction of ovulation which can be achieved with an injection of either GnRH (Pursley et al. 1997)or oestradiol benzoate (ODB) (Day et al. 2000). A comparative study investigating corpus luteum (CL) and follicular emergence after the administration of either GnRH or ODB at pro-oestrus has not been reported. It was hypothesised that the injection of ODB at pro-oestrus would delay emergence of the first post-ovulatory follicular wave, but that CL development and plasma progesterone concentrations would be similar in cows induced to ovulate with either GnRH or ODB.