To determine the duration and hormonal characteristics of the oestrous cycle in scimitar-horned oryx, ovulation was synchronized in 11 females using exogenous progesterone and a prostaglandin analogue. Daily blood samples were taken from six animals during 46 days (with a 7-day hiatus). The remaining five animals were blood sampled every 30 min for 6 h on three occassions druing 22 days, then resynchronized with prostaglandin analogue and pregnant mare's serum gonadotrophin and blood sampled daily for another 21 days (with a 7-day hiatus). Behavioural observations were made on days 1 through 3 and 24 through 28 to determine the occurrence of oestrus.
Only animals > 2 years old (n= 7) had plasma progesterone concentrations indicative of luteal function, with a mean luteal phase progesterone concentration of 13.6 ± 3.3 (S.E.) nmol.l−1 and a mean follicular phase concentration of < 3.2 nmol.l−1. Mean duration of the oestrous cycle estimated from plasma progesterone profiles and behavioural data 22.7 ± 1.1 (S.E.; n= 7) days, range 17-25 days. When estimated from behavioural data alone, mean duration of the oestrous cycle was 22.3 ± 0.3 (S.E.; n= 3) days, range 22-23 days. Mean length of the luteal phase was 17.3 ± 0.6 (S.E.; n= 8) days, range 14-19 days, and mean length of the follucular phase was 5.6 ± 0.5 (S.E.; n= 5) days, range 3-7 days. Pulses in plasma LH concentration detected by Cluster analysis ranged from 0.34-1.55ng.ml−1 in animals ≷ 2 years old (n= 3), and from 0.17-0.29ng.ml−1 in animals < 2 years old (n= 2), the difference in mean pulse height being significant (P < 0.01). No difference in mean plasma LH concentration was detected due to stage of cycle. Elevations in plasma oestradiol-17β concentration were observed at or preceding oestrus in three animals and during the mid-luteal phase in three animals.
A significant decrease in haematocrit with time was recorded for blood samples from the third serial bleed. This was greater (P > 0.01) in animals > 2 years of age (n= 3), suggesting that these older animals adapted better to the stress of repeated sampling. Plasma cortisol concentrations also declined throughout the serial bleed but there was no difference in this decline between the two age groups.
Results of this study define the duration of the oestrous cycle in scimitar-horned oryx and show that its hormonal components are similar to the well-characterized patterns of other species, especially cattle.