Aim.

To evaluate the effect of estradiol benzoate (EB) and an intravaginal progesterone implant to synchronize the estrus and ovulation of the high tropics mares.

Methods:

A number of 24 creole mares were included in the study, distributed in two groups: T1=10 mg and T2 =25 mg of estradiol benzoate. The development of the dominant follicle (DF) was evaluated after the treatment, along with the levels of estradiol every 48 hours, until a new follicular wave occurred. Later, subgroups were arranged according to the start day of follicular wave occurrence during treatment 1 (T1_4d and T1_6d), and treatment 2 (T2_4d and T2_10d).

Results:

The mean DF size values in the two treatments (T1 and T2) were similar until day 4, then DF decreased gradually in T1, whereas T1 showed an increase until day 8, and the atresia process began. The restart of the follicular wave took place on the fourth day of treatment 1, and on the fourth and tenth days of treatment 2. The time between the withdrawal of the implant and ovulation was similar in the subgroups: (T1_4d) treatment 1 and T2_4d, treatment 2. However, they differed from the other two subgroups observed in T1 and T2.

Conclusion:

The utilization of 10 mg estradiol benzoate along with a progesterone implant enabled better synchronization of the beginning of the follicular wave in a 4-6 post-treatment-day window (averaging 5 days).