Presynch Ovsynch

Response to the Ovsynch® protocol is optimized when cows ovulate after the first GnRH injection of the protocol and when a responsive CL is present at the moment of the PGF2a treatment. Ovulation after the first GnRH injection and initiation of a new follicular wave should improve PR because a follicle with a reduced period of dominance is induced to ovulate. Furthermore, initiating the Ovsynch® protocol prior to day 12 of the estrous cycle should minimize the number of cows that come into estrus prior to the second GnRH injection and ovulate prior to the completion of the protocol.

A presynchronization protocol was developed[3] to optimize the Ovsynch® protocol by giving two injections of PGF2a 14 days apart, with the second injection given 12 days before initiating the Ovsynch® protocol (Fig. 2). The Presynch-Ovsynch® protocol increased PR by 18% (i.e., 25 to 43%) in cyclic cows. Success of the Ovsynch® protocol is dependent on whether lactating cows are anestrus (22% PR) or cycling (42% PR). If anestrous cows ovulate after the first and second GnRH injections of the Ovsynch® protocol, PR appeared to be normal (e.g., 39%). Intravaginal inserts of progesterone administered as

Estrus detection and Al

7 days

48 hours

12 to 16 h

-1—

-1-

Fig. 1 Ovsynch® protocol for timed AI.

part of the Ovsynch® protocol (i.e., between GnRH and PGF2a injections) also may benefit anestrous animals. Future protocols for further optimization of fertility likely will involve an initiation of follicular turnover via either induction of ovulation (i.e., GnRH) or follicular atresia (i.e., estrogens) in all cows, and maintenance of luteal phase progesterone concentrations with an intravaginal insert until induced CL regression.

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