Ultrasonographic characterization of ovarian events and fetal gestational parameters in two southern black rhinoceros (Diceros bicomis minor) and correlation to fecal progesterone

A tremendous potential exists for the application of transrectal ultrasonog raphy as a tool to enhance the captive management of endangered species. Re productive study of two southern black rhinoceros (Diceros bicornis minor) females was performed daily to every other day for a similar to 60 day peri od to document ovarian changes, and three times weekly in early pregnancy t o once monthly in late pregnancy in order to characterize changes in fetal parameters throughout gestation. All ovarian and fetal anatomical structure s were measured in millimeters. The mean (+/- SD) length of the estrous cyc le or interovulatory period was 26 +/- 1.4 days (n=2 cycles). Follicular gr owth rate of a dominant follicle was similar to3 mm/day once the follicle r eached 35 mm in diameter. Ovulation was observed to occur at a mean (+/- SD ) follicular diameter of 49.5 +/- 2.6 mm (n=4) and within 48 to 72 h after observed estrus (n=2). Large ovarian structures [mean (+/- SD) diameter of 71.7 +/- 2.9 mm; n=3], considered analogous to equine anovulatory hemorrhag ic follicles, were observed to form in the winter months and suggest season al periods of reduced fertility. Fecal progesterone assays confirmed ultras onographic events. Although preliminary, the results of fetal sexing are pr esented and compared to the horse. Our data indicate that fetal eye or feta l foot diameter measurements can be used to accurately predict gestational age from about 2 months to term, providing useful information to managers o f both captive and wild rhino populations. The ability to identify and quic kly release animals in late term pregnancy in the wild and thereby reduce a bortions and neonatal mortalities in holding bomas is one potential practic al conservation benefit of the fetal age predictive models. (C) 2001 by Els evier Science Inc.