Evaluation of presynchronized resynchronization protocols for lactating dairy cows.

Area of Science:

• Reproductive endocrinology and artificial insemination in cattle.

Background:

• Optimizing artificial insemination (AI) protocols in lactating dairy cows is crucial for reproductive efficiency.
• Presynchronization of the estrous cycle aims to improve timed AI outcomes.
• The role of controlled internal drug-releasing (CIDR) inserts in timed AI protocols requires further investigation.

Purpose of the Study:

• To determine the reinsemination speed and pregnancy per AI (P/AI) in cows presynchronized with GnRH or PGF(2α).
• To evaluate the effect of CIDR insert treatment during timed AI on P/AI in presynchronized cows.

Main Methods:

• Lactating cows were presynchronized with GnRH (GGPG) or PGF(2α) (P11GPG) before a timed AI protocol.
• Cows were reinseminated upon estrus detection or at a fixed time.
• A subset received a CIDR insert during the timed AI protocol; P/AI was assessed at 32 and 67 days post-reinsemination.

Main Results:

• P11GPG treatment resulted in faster reinsemination rates and shorter intervals to reinsemination compared to GGPG.
• Presynchronization treatment did not significantly impact overall P/AI at 32 or 67 days.
• CIDR insert treatment during timed AI did not affect P/AI.

Conclusions:

• Presynchronization with GnRH or PGF(2α) yielded similar pregnancy per AI rates in lactating cows.
• PGF(2α) presynchronization may reduce the interval to pregnancy establishment in herds with high estrous detection efficiency.
• CIDR insert use during timed AI did not enhance pregnancy outcomes in this study population.