Ovarian follicular dynamics and hormonal secretory profiles in guanacos (Lama guanicoe)

The objective of the present study was to describe ovarian activity in 11 adult non-mated guanacos, evaluated every second day for 40 days by transrectal ultrasonography and by plasma estradiol-17β and progesterone concentrations. An inverse relationship (r = −0.29, P < 0.001) was observed between the diameter of the largest ovarian follicle and the total number of follicles indicating that follicular growth in guanacos occurs in waves. The mean duration of follicular wave was 15.1 ± 4.2 days with a range from 9 to 26. The follicular growth phase was 7.0 ± 2.4 days, the static phase 3.0 ± 1.2 days, the regression phase 5.2 ± 2.1 days and the inter-wave interval was 12.6 ± 5.6 days. The maximum follicular diameter in each follicular wave was 10.2 ± 2.1 mm with a range from 7.2 to 16.1 mm. Inter-wave intervals of longer duration were associated with a larger maximum follicle diameter (P < 0.001). Follicular activity alternated between ovaries in 93% of the waves with 48% of dominant follicles occurring in the left and 52% in the right ovary without differences (P > 0.05). Plasma estradiol-17β concentrations showed a wave-like pattern, varying from 20.0 to 92.1 pmol/L. Plasma progesterone concentrations remained below 1 nmol/L without any ultrasonic evidence of ovulation during the study. These results in guanacos suggest a follicular wave pattern more similar to the llama (Lama glama) than previously described in other South American and Old World camelid species.