The objective of this research was to characterize the follicular dynamics in heifers of the Simmental Fleckvieh breed in tropical savanna climate conditions. Sixteen estrous cycles were studied in eight animals (two consecutive cycles per animal). Significant statistical differences were found for the number of small follicles between cycles (P < 0.001) and between waves (P < 0.001). The largest number of small follicles before selection of the dominant follicle were observed between days 2. 00 and 4. 00 after the start of the growth of a new wave. The diameter reached by the pre-ovulatory dominant follicle of the second wave (15.05 mm) was significantly greater (P < 0.05) than that of the dominant wave follicle (12.70 mm). In conclusion, the number of follicles that emerge in each estrous cycle and each wave of follicular development is different even in the same animal. The day with the largest number of small follicles occurs at the beginning of the wave of follicular development. The pre-ovulatory follicles reach a greater diameter than the dominant follicles of the first wave.
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