Utilization of Urinary Neopterin Levels for Pregnancy Diagnosis in Mated Giant Pandas

Neopterin is a well-characterized marker of cell-mediated immunity. Here, we used neopterin as a biomarker to identify the cellular immunity status of breeding giant pandas throughout gestation. Urine samples were collected from captive adult female giant pandas that had entered estrus and were either naturally bred and/or artificially inseminated (AI) during the breeding seasons at the Chengdu Research Base of Giant Panda Breeding. This study was divided into two parts. In the first part, we examined the urinary neopterin and progesterone (Pg) profiles during pregnancy in parturient and nonparturient individuals. From the day of mating to the Pg peak, there was no correlation between neopterin and Pg in both parturient individuals (n = 3) and nonparturient individuals (n = 3). During the period when the Pg dropped from its peak to approximately 100 ng/mg Cr, the changes in neopterin and Pg showed a negative correlation in parturient individuals, while there was no correlation between the changes in neopterin and Pg in nonparturient individuals. Subsequently, urine samples were categorized into four phases based on the reproductive status of giant pandas: (1) Estrus phase (Es); (2) Primary Pg increase phase (S1), during which Pg levels rise from the day of mating to 100 ng/mg Cr; (3) Secondary Pg increase phase (S2), during which Pg levels rise from 100 ng/mg Cr (inclusive) to their peak value; and (4) Post-peak Pg decline phase (S3), during which Pg levels decrease from their peak (inclusive) until they drop to approximately 200 ng/mg Cr. Analysis revealed that differences between parturient and nonparturient females emerged in the S3 phase. Compared to nonparturient individuals, neopterin concentrations showed sustained elevation in parturient pandas during the S3 phase. The second part of the study, building on the findings of the first part, specifically focused on analyzing the urine samples of giant pandas during the S2 and S3 phases. Statistical analysis of an expanded sample of individuals (including those from the first part) revealed a significant difference in the neopterin mean S3/S2 ratio between the parturient group (mean S3/S2 = 1.71 ± 0.12; n = 14) and the nonparturient group (mean S3/S2 = 0.85 ± 0.04; n = 17). Correspondingly, parturient individuals gave birth 5 to 16 days after the end of the S3 phase (this time corresponds to the point when Pg levels decrease to approximately 200 ng/mg Cr). The results revealed the validity and applicability of using the neopterin mean S3/S2 ratio (1.71 ± 0.12) for diagnosing successful pregnancy in mated female giant pandas.