Placentation in the plains zebra (Equus quagga)
W. R. (Twink) Allen A B C , Fiona Stansfield A and Sandra Wilsher A B
+ Author Affiliations
- Author Affiliations
A The Paul Mellon Laboratory of Equine Reproduction, ‘Brunswick’, 18 Woodditton Road, Newmarket, Suffolk CB8 9BJ, UK.
B Present address: Sharjah Equine Hospital, Airport Road, Bridge No.6, Al Atain Area, Sharjah, United Arab Emirates.
C Corresponding author. Email: twinkallen100@gmail.com
Reproduction, Fertility and Development 29(11) 2225-2234 https://doi.org/10.1071/RD16475
Submitted: 26 November 2016 Accepted: 13 February 2017 Published: 30 March 2017
Abstract
The placenta and fetal gonads of 12 pregnant plains zebra (Equus quagga), estimated to be between 81 and 239 days of gestation, were examined. The diffuse, microcotyledonary zebra placenta appeared, developmentally, to be 3–4 weeks behind its counterpart in horse pregnancy and this, together with the presence of small and long-lived endometrial cups, low levels of zebra chorionic gonadotrophin in maternal serum and few accessory corpora lutea in the maternal ovaries during the first half of gestation, made zebra pregnancy more similar to donkey than horse pregnancy. Zebra fetal gonads enlarged after 80 days of gestation and their interstitial cells stained positively for 3β hydroxysteroid dehydrogenase and 17,20 lyase steroid enzymes while the trophoblast stained for aromatase. This confirmed that zebra fetal gonads, like those of the horse and donkey, can synthesise C19 androgens, which can then be aromatised by the placenta to C18 oestrogens. It is remarkable that such unusual feto–placental mechanisms of production of gonadotrophic and steroid hormones has persisted unchanged within the genus Equus despite the many physical adaptations and the considerable loss of chromosomes that have occurred during the evolution of its member species.
Additional keywords: chorionic gonadotrophin, endometrial cups, fetal gonads, placenta, sex steroids
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