Equine chorionic gonadotropin administered on day 5 of a 7-days fixed-time artificial insemination program improves ovulation synchrony and corpus luteum function in anestrous beef cows.

The research aimed to study whether administering equine chorionic gonadotropin (eCG) on Day 5 of a fixed-time artificial insemination program can help improve ovulation synchrony and functionality of the corpus luteum in anestrous beef cows. The study found that administering eCG on Day 5 yielded better results compared to doing the same on Day 7, with better corpus luteum function and an 11.2% increase in conception rates.

Experimental Design

• Two experiments were conducted to assess the effects of eCG. Experiment 1 focused on determining the preovulatory follicle diameter, ovulation time, corpus luteum area, and estradiol and progesterone concentrations. Experiment 2, on the other hand, was a field trial aimed at evaluating the conception rate.
• For both experiments, a synchronization protocol was set up utilizing estradiol benzoate (EB) on Day 0, intravaginal progestin device (IVD) from Days 0 to 7, prostaglandin (PGF) on Day 7, eCG on Day 5 or 7, and GnRH on Day 9.
• Treatment consisted of administering 400 IU of eCG either on Day 5 (T5) or Day 7 (T7), aligned with prostaglandin (PGF2α) treatment.

Findings from Experiment 1

• By 16 hours after GnRH administration on Day 9, all cows from the T5 group ovulated. There was an indication that the preovulatory follicle tended to be larger at 1 and 2 days prior to ovulation in T5 cows.
• One day before ovulation, estradiol levels were slightly lower in the T5 group than in the T7 group, although this was not statistically significant.
• However, the corpus luteum area and progesterone levels were significantly greater in the T5 group on Day 9 as compared to the T7.

Findings from Experiment 2

• The conception rate was significantly higher in the T5 group (72.2%) as compared to the T7 group (61.0%).

Conclusion

• The administration of eCG on Day 5 of the fixed-time artificial insemination protocol seemed to advance ovulation with a larger follicle. This resulted in a larger corpus luteum and higher progesterone productions by Day 9 post-ovulation, leading to a 11.2% increase in pregnancy rates in cows.