The objective of this research was to characterize the follicular dynamics in heifers of the Simmental Fleckvieh breed under Tropical savanna climate conditions. Sixteen estrous cycles were studied in eight animals (two consecutive cycles per animal). A greater number of estrous cycles were observed with two waves of follicular development (81.25%), followed by those of three and four waves. Longer estrous cycles (23 days) were found in the patterns of four waves of follicular development, while the patterns of two and three waves presented shorter cycles (19 and 22 days respectively). The beginning of the follicular wave, for the three observed patterns, occurred between the day zero and one of the cycle, while the following waves (two and three) always emerged one to three days earlier in the cycles with patterns of greater number of waves. The corpus luteum (CL), was seen between day three and day five of the cycle, which reached a maximum diameter of 2.23 cm on average, and began its regression around day 15.63. We conclude that Simmental Fleckvieh heifers under tropical climate conditions tend to manifest estrus cycles mostly with two wave patterns of follicular development and therefore, these cycles tend to be longer than the reported 21-day cycle in the classical literature. In the same way, they presented a good luteal development with the capacity to prepare the uterus for pregnancy and favoring implantation.
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