Effects of lactational and reproductive status on ovarian follicular waves in llamas (Lama glama)

Abstract

The effects of lactational status and reproductive status on patterns of follicle growth and regression were studied in 41 llamas. Animals were examined daily by transrectal ultrasonography for at least 30 days. The presence or absence of a corpus luteum and the diameter of the largest and second largest follicle in each ovary were recorded. Llamas were categorized as lactating (N = 16) or non-lactating (N = 25) and randomly allotted to the following groups (reproductive status): (1) unmated (anovulatory group, N = 14), (2) mated by a vasectomized male (ovulatory non-pregnant group, N = 12), (3) mated by intact male and confirmed pregnant (pregnant group, N = 15). Ovulation occurred on the 2nd day after mating with a vasectomized or intact male in 26/27 (96%) ovulating llamas. Interval from mating to ovulation (2.0 ± 0.1 days) and growth rate of the preovulatory follicle (0.8 ± 0.2 mm/day) were not affected by lactational status or the type of mating (vasectomized vs intact male). Waves of follicular activity were indicated by periodic increases in the number of follicles detected and an associated emergence of a dominant follicle that grew to ≥ 7 mm. There was an inverse relationship (r = -0.2; P = 0.002) between the number of follicles detected and the diameter of the largest follicle. Successive dominant follicles emerged at intervals of 19.8 ± 0.7 days in unmated and vasectomy-mated llamas and 14.8 ± 0.6 days in pregnant llamas (P = 0.001). Lactation was associated with an interwave interval that was shortened by 2.5 ± 0.05 days averaged over all groups (P = 0.03). Maximum diameter of anovulatory dominant follicles ranged from 9 to 16 mm and was greater (P < 0.05) for non-pregnant llamas (anovulatory group, 12.1 ± 0.4 mm; ovulatory group, 11.5 ± 0.2 mm) than for pregnant llamas (9.7 ± 0.2 mm). In addition, lactation was associated with smaller (P < 0.05) maximum diameter of dominant follicles averaged over all reproductive statuses (10.4 ± 0.2 vs 11.7 ± 0.3 mm). The corpus luteum was maintained for a mean of 10 days after ovulation in non-pregnant llamas and to the end of the observational period in pregnant llamas. The presence (ovulatory non-pregnant group) and persistence (pregnant group) of a corpus luteum was associated with a depression in the number of follicles detected and reduced prominence of dominant follicles (anovulatory group > ovulatory non-pregnant group > pregnant group). Lactation was also associated with reduced prominence of dominant follicles. The results demonstrate that follicular activity occurred in waves for llamas of all types of reproductive status and that lactation and the presence of a corpus luteum were associated with depressed follicular development.