Pattern of faecal 20-oxopregnane and oestrogen concentrations during pregnancy in wild plain zebra mares

Abstract

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.