Faecal oestrogen and progestin analyses were used to assess ovarian activity in non-pregnant scimitar-horned oryx (Oryx dammah) during a 13-month interval. Mean (± SE) luteal phase, interluteal
phase and oestrous cycle duration were 18.8 (± 0.5), 5.1 (± 0.2) and 23.8 (± 1.3) days, respectively.
All females exhibited a synchronized anovulatory period that ranged from 36–95 days during spring.
Short ovarian cycles (10.6 (± 0.8) days) were observed intermittently throughout the year and before
the spontaneous resumption of oestrous cyclicity. Periovulatory peaks in oestrogen concentrations
were detected for 42.5% (31/73) of ovarian cycles. A parallel analysis of reproductive data from the
North American studbook (1985–1994) revealed that captive-held scimitar-horned oryx gave birth
throughout the year. Sex ratio at birth was male-biased (54.4%), and 19.1% of all calves failed to
survive to 6 months of age (220 out of 1149 births). Only 0.7% of births resulted in twins. Median
interbirth interval was 277 days, and 75% of these intervals were less than 332 days. Interbirth interval
was extended (P < 0.05) if parturition occurred from January through May. In summary, the scimitar-horned oryx is a seasonally polyoestrous species that experiences a distinct anovulatory period
during spring in north-east America.