Urinary estrogens as a non-invasive biomarker of viable pregnancy in the giant panda (Ailuropoda melanoleuca)

Abstract

Female giant pandas show complex reproductive traits, being seasonally monoestrus, displaying a variable length embryonic diapause and exhibiting pseudopregnancy. Currently, there is no confirmatory non-invasive biomarker of blastocyst implantation or pregnancy. This study aimed to monitor urinary estrogens across gestation in pregnancy (n = 4), pseudopregnancy (n = 4) and non-birth cycles (n = 5) in the giant panda. A pregnancy-specific profile of estrogens corrected for urinary specific gravity was identified during the gestation period. Pregnant females showed increasing concentrations of estrogens for 29 days until birth, no increase was observed during pseudopregnancy and the two profiles were distinguishable from each other for the final 2 weeks of the cycle suggesting the estrogens are of placental origin. This allowed a nomogram, starting at a known fixed point during the cycle, to be created and tested with cycles of known outcome, and cycles which were inseminated but did not result in a birth. Non-birth profiles showed deviations from that of pregnancy. We believe these deviations indicate the point of failure of the placenta to support a developing cub. Non-invasive longitudinal monitoring of estrogen concentrations therefore has the potential to be developed as a panda pregnancy test to predict viable cub development.

Evolutionary survival strategies of the female giant panda: optimizing energy resources and expenditure prior to pregnancy by postponing corpus luteum reactivation

“…As an artefactual result, creatinine-corrected progesterone levels showed an earlier increase because of extremely low creatinine values correlated to weight gain and reduced activity, and thus altered muscle tissue metabolism, during late corpus luteal dormancy phase. Since the active luteal phase is associated with acute, dramatic metabolic shifts, USpG-corrected estrogen profiles – but not creatinine-corrected - during late active luteal phase were discriminative for pregnancy and indicative for feto-placental involvement [78].…”

“…For SB569 and SB884 (2017, 2018), estrogens were determined by the DetectX ® Estrone-3-glucuronide (E1G) Enzyme Immunoassay Kit (K036-H5, Arbor Assays™, Ann Arbor, Michigan, USA), while for the other cycles the DetectX ® Estrone Enzyme Immunoassay Kit (K031-H1, Arbor Assays™, Ann Arbor, Michigan, USA) was used with estrone-3-sulphate (E1S) as standard [77]. Wilson et al (2019) described a conversion factor of 2.62, which was used in this study to convert E1G values into E1S-estimates [78].…”

Could embryonic diapause facilitate conservation of endangered species?

“…Firstly, as described for other bear species, in all ovulated giant pandas the reproductive system is being pre-programmed for potential pregnancy [32,33]. Hence, no differences in hormone profiles have so far been observed between pregnant and pseudopregnant animals until after the window of implantation/attachment (see Figure 1) [34], in contrast to the later stage of the active luteal phase [35]. Secondly, to maintain a potential pregnancy, all females need the period of diapause to gain enough weight (energy resources) to survive the short pregnancy with the attendant exponential growth of the embryo [36].…”

The novel use of urinary androgens to optimise detection of the fertile window in giant pandas

“…A secondary luteal phase follows, which has a more significant progestogen rise and a more consistent duration (45 -50 days), which is when fetal development takes place (Steinman et al 2006;Kersey et al 2010b). Progestogen measurements cannot be used as a pregnancy marker due to the occurrence of pseudopregnancy in giant pandas; indeed, both the progesterone metabolite profile and the behavioural changes are similar in pregnant and non-pregnant females (Monfort et al 1989;Steinman et al 2006;Zhang et al 2009;Kersey et al 2010a;Kersey et al 2010b;Willis et al 2011;Roberts et al 2018;Wilson et al 2019). With more giant panda pairs being loaned outside of China as part of international breeding programmes, there is an increased interest in enhancing the understanding of the female reproductive physiology.…”

“…With more giant panda pairs being loaned outside of China as part of international breeding programmes, there is an increased interest in enhancing the understanding of the female reproductive physiology. Recent studies have focussed on determining pregnancy status (Willis et al 2011;Cai et al 2017;Roberts et al 2018;Wilson et al 2019). However, there is an additional need for research into other phases of the reproductive cycle, including the prediction of estrus timing.…”