ENDOCRINE PROFILES DURING THE ESTROUS-CYCLE AND PREGNANCY IN THE BAIRDS TAPIR (TAPIRUS-BAIRDII)

Serum samples were collected 1-3 times weekly from two Baird's tapirs (Tapirus bairdii) for 6 months in 1987-1988, and for more than 3 conse cutive years beginning in 1989 to characterize hormone patterns during the estrous cycle and pregnancy. Based on serum progesterone concentr ations, mean (+/-SEM) duration of the estrous cycle (n = 20) was 30.8 +/- 2.6 days (range, 25-38 days) with a luteal phase length of 18.1 +/ - 0.4 days (range, 15-20 days). Mean peak serum progesterone concentra tions during the luteal phase were 1.35 +/- 0.16 ng/ml, and nadir conc entrations were 0.19 +/- 0.03 ng/ml during the interluteal period. Dis tinct surges of estradiol preceded luteal phase progesterone increases in most (14/20) cycles. Gestation length was 392 +/- 4 days for three complete pregnancies. Mean serum progesterone concentrations increase d throughout gestation and were 1.83 +/- 0.13, 2.73 +/- 0.13, and 4.30 +/- 0.16 ng/ml during early, mid- and late gestation, respectively. S erum estradiol concentrations began to rise during mid-gestation, incr easing dramatically during the last week of pregnancy. Patterns of ser um estriol and estrone secretion during pregnancy were similar to that observed for estradiol. In contrast to progesterone and estrogens, se rum cortisol concentrations were unchanged during pregnancy or parturi tion. Females resumed cycling 16.2 +/- 2.0 days after parturition (n = 4) and, on two occasions, females became pregnant during the first po stpartum estrus. These data suggest that the tapir cycles at approxima tely monthly intervals and that increases in serum progesterone are in dicative of luteal activity. The interluteal period is relatively long , comprising approximately 40% of the estrous cycle. During gestation, progesterone concentrations are increased above luteal phase levels, and there is evidence of increased estrogen production during late ges tation. The absence of increased cortisol secretion at the end of gest ation suggests that this steroid does not play a major role in initiat ing parturition in this species. (C) 1994 Wiley-Liss, Inc.