Reproductive cycle length and pregnancy in the southern white rhinoceros (Ceratotherium simum simum) as determined by fecal pregnane analysis and observations of mating behavior

Pregnancy and the reproductive cycle were monitored in 13 captive southern white rhinoceros (Ceratotherium simum simum) by measuring progesterone meta bolites in fecal extracts and by observing behavior patterns. Fecal hormone s were measured using a monoclonal antibody produced against 4-pregnen-11-o l-3,20-dione hemisuccinate:BSA. Several subjects exhibited flat or erratic endocrine profiles, but we found evidence for 17 reproductive cycles in fiv e females. Mating behavior coincided with nadirs in pregnane concentrations . These cycles appeared to fail into two general categories: those of appro ximately 1 month in duration (Type I: (X) over bar +/- SEM = 35.4 +/- 2.2 d ays; n = 10) and those lasting approximately 2 months (Type II: 65.9 +/- 2. 4 days; n = 7). Interluteal phase lengths were similar for the two cycle ty pes, but Type II cycles were characterized by extended luteal phases lastin g more than twice as long as Type I luteal phases. Because Type I cycles pr edominated in our data and because evidence suggests that some Type LT cycl es may be aberrant, we argue that these approximately monthly cycles repres ent the typical reproductive cycle for this species. Three females became p regnant during the course of the study. We were able to detect pregnancy by approximately 3 months post-breeding, as indicated by sustained pregnane c oncentrations markedly higher than nonpregnant luteal phase concentrations. These data help to characterize important reproductive events of this spec ies and should be useful for captive breeding efforts for this threatened s pecies. (C) 1999 Wiley-Liss, Inc.