Ultrasound and endocrine evaluation of the ovarian cycle and early pregnancy in the Sumatran rhinoceros, Dicerorhinus sumatrensis

Longitudinal ultrasound and endocrine evaluations were conducted in two adu lt female Sumatran rhinoceroses (Dicerorhinus sumatrensis) over a period of 12-22 months to learn move about their reproductive physiology. Rectal ult rasonography was conducted to monitor ovarian activity. Blood samples were collected and analysed for progesterone and LH, and faecal samples were ana lysed for progestin metabolites. One female showed cyclic ovarian activity during the study period, whereas the other female showed no evidence of ova rian activity. The cyclic Sumatran rhinoceros appeared to be an induced ovu lator, the first of its kind reported within the Perrisodactyla. Ultrasound examinations of the ovaries revealed the formation of anovulatory haemorrh agic follicles when the animal was not mated. These follicles appeared to u ndergo varied degrees of luteinization that resulted in irregular faecal pr ogestin profiles. When allowed to mate, the female showed a 21 day reproduc tive cycle that was reflected in both faecal progestin and serum progestero ne profiles. The concentration of serum LH was baseline before mating, incr eased approximately 30-fold within 1-2 h of intromission and returned to ba seline within 22 h. Ovulation occurred within 46 h of copulation. The femal e conceived three times during the study, pregnancy was detected using ultr asonography 14-16 days after mating, and the concentration of both serum pr ogesterone and faecal progestins remained high. Early embryogenesis appeare d to be similar to that in horses. However, each pregnancy terminated unexp ectedly within the first 3 months of gestation. This study demonstrates the important role that basic research and reproductive technology can play in developing a natural breeding programme for an endangered animal in captiv ity.