[Use of PGF2alpha and GnRH for estrus synchronization in cattle]

Estrus detection has a tremendous impact on the reproductive efficiency in dairy farms. Recently the systematic use of hormones for synchronization of estrus and ovulation has been propagated. These programs are designed to facilitate estrus detection and/or increase its efficiency. Prostaglandin programs are used to improve estrus detection and reproductive management in dairy operations. All cows are treated up to three times in weekly or biweekly intervals at the end of the voluntary waiting period. This should lead to groups of cows in estrus within two to four days after PG treatment. Since PG programs cannot completely eliminate the need for estrus detection procedures for fixed time artificial insemination (AI) were developed. Fixed time AI not only requires control of the luteal phase of the cow but also synchronization of the follicular development. Treatment with GnRH will induce a new follicular wave and provide a dominant follicle in a defined growth phase at the time of PG administration seven days later. A second injection of GnRH given 48 hours after PG results in ovulation approximately 24 to 32 hours after GnRH (OvSynch-procedure). The pros and cons of hormone programs in dairy farming are discussed in the light of field trials and experiments performed in our department.