Endocrine and ultrasonographic characterization of a successful pregnancy in a Sumatran rhinoceros (Dicerorhinus sumatrensis) supplemented with a synthetic progestin

A Sumatran rhinoceros with a history of early pregnancy loss was supplemented with a synthetic progestin, altrenogest (Regu-Mate(R)), and delivered a healthy, full-term calf 475 days after mating. Serum hormone concentrations were measured throughout gestation, and ultrasonography was used to monitor embryo/fetal growth and viability. The embryonic vesicle growth curve was characterized by three phases: rapid expansion, plateau, and a final rapid expansion, and was similar to that in the domestic horse. Fetal sex was determined by ultrasound on day 73 of gestation. After day 80 of gestation, transabdominal examinations were more useful than rectal examinations for imaging the fetus. Serum progesterone concentrations remained at luteal levels (1.5 +/- 0.5 ng/ml) for the first 2 months of pregnancy, and then they gradually increased. However, progesterone decreased almost to luteal levels during the fifth month before it increased again, and eventually reached peak concentrations (13.3 +/- 1.9 ng/ml) shortly before parturition. Relaxin concentrations remained basal (less than or equal to 0.5 ng/ml) for the first half of the pregnancy, increased to 2.7 +/- 1.2 ng/ml and stabilized until 2 weeks before parturition, when relaxin spiked to unusually high concentrations (800-1300 ng/ml). Prolactin concentrations were at baseline (7.2 +/- 1.7 ng/ml) throughout Most of the gestation, but rose markedly 2 weeks before parturition, reaching concentrations as high as 75 ng/ml. Attempts to measure serum estrogen concentrations were unsuccessful. These data represent the first attempt to characterize pregnancy in the critically endangered Sumatran rhinoceros, a species that heretofore had not successfully reproduced in captivity for 112 years. (C) 2004 Wiley-Liss, Inc.