Regulative endocrine mechanisms influence the reproductive behaviour and success of mammals, but
they have been studied predominantly in domestic and captive animals. The study aims at describing
the pattern of faecal 20-oxopregnane and oestrogen concentrations during pregnancy in wild plains zebra
Equus quagga chapmani. Data were collected during wet and dry seasons 2007–2009. Enzyme Immunoassays
were used to determine 20-oxopregnane and oestrogen concentrations in faecal samples (n = 74)
collected from individual mares (n = 32) whose dates of foaling were known through long-term monitoring.
Hormonal profiles were described with a General Additive Model (GAM: Hormone Days to Foaling).
Faecal 20-oxopregnanes have a complex cycle during pregnancy (GAM, n = 70, R2 = 0.616,
p < 0.001). From 250 days to foaling, faecal 20-oxopregnane concentrations were above the baseline
levels found in non-pregnant mares, peaking in the last 50 days. Faecal oestrogen levels showed a clear
peak in mid-pregnancy (GAM, n = 62, R2 = 0.539, p < 0.001). The sex of the foetus and season had no
detectable effect on hormone concentrations during pregnancy. High levels (>200 ng/g DW) of faecal
20-oxopregnanes associated with high (>160 ng/g DW) faecal oestrogen levels indicate mid-pregnancy
in c.90% of cases (16/17). High faecal 20-oxopregnanes (>200 ng/g DW) and low faecal oestrogen levels
(<160 ng/g DW) indicate late pregnancy, again in c.90% of cases. Two faecal samples would allow the
stage of pregnancy to be determined with confidence.