Evaluation of short estrus synchronization methods in dairy cows

Area of Science:

• Veterinary Medicine
• Reproductive Biology
• Animal Science

Background:

• Estrus synchronization is crucial for efficient reproductive management in lactating dairy cows.
• Existing protocols may have limitations in terms of efficacy and applicability across different reproductive stages.
• Optimizing estrus synchronization can improve artificial insemination (AI) success rates and overall herd fertility.

Purpose of the Study:

• To develop and evaluate two novel short-term estrus synchronization protocols for lactating dairy cows.
• To compare the efficacy of these protocols in terms of estrus response, ovulation rates, and pregnancy rates.
• To investigate the influence of the estrus cycle stage on the success of timed AI following synchronization.

Main Methods:

• Three experiments were conducted involving lactating dairy cows.
• Experiment 1 and 2 tested different timings of PGF2alpha, estradiol propionate (EP), and GnRH for estrus synchronization and timed AI (TAI).
• Experiment 3 evaluated treatments initiated at specific estrus cycle stages (metestrus, diestrus, proestrus) with subsequent TAI and monitored luteal development.

Main Results:

• Cows with an active corpus luteum (CL) at the start of Experiment 1 showed significantly higher estrus rates.
• Experiment 2 demonstrated higher synchronized ovulation rates compared to Experiment 1 (94.1% vs. 59.1%).
• In Experiment 3, the proestrus group exhibited significantly higher estrus and pregnancy rates compared to the metestrus group; pregnancy rates in Exp 1 and 3 were comparable to natural estrus insemination.

Conclusions:

• The developed estrus synchronization protocols can achieve pregnancy rates comparable to natural estrus in lactating dairy cows.
• The timing of hormonal treatments and the stage of the estrus cycle at treatment initiation significantly influence synchronization efficacy and pregnancy outcomes.
• The proestrus stage appears most favorable for achieving higher pregnancy rates following the tested synchronization protocols.