Follicular activity and hormonal secretory profile in vicuna ( Vicugna vicugna)

Abstract

The objective of the present study was to characterize ovarian activity in non-mated vicunas, relating ovarian structures (evaluated by transrectal ultrasonography, daily for 30 days) to changes in plasma concentrations of estradiol-17β and progesterone. Ovarian follicular activity occurred in waves, characterized by the follicle emergence, growth and regression. The mean duration of follicular waves was 7.2±0.5 days (mean±S.E.M.), with a range of 4–11 days. The follicular growth phase averaged 3.0±0.2 days, the static phase 1.4±0.1, the regression phase 2.9±0.3 days, and the inter-wave interval was 4.2±0.3 days. The mean growth rate during the growing phase was 1.8±0.1 mm/day, while the duration of the interval from 6 mm to maximum diameter was 1.4±0.1 days. The mean maximum diameter of the dominant follicle was 8.4±0.3 mm (range: 6.2–11.2) and mean diameter of the largest subordinate follicle was 5.4±0.1 mm. There was an inverse relationship between the size of the largest follicle and the total number of follicles ( r=−0.21, P=0.002). Follicle activity alternated between ovaries in 77% of the waves, with 40% of dominant follicles present in the left ovary and 60% in the right ovary. Plasma estradiol-17β concentrations also had a wave-like pattern, varying between 12.0 and 62.8 pmol/l. Plasma progesterone concentrations remained below 5.0 nmol/l and there was no ultrasonographic evidence of ovulation during the study.