The current study was conducted in several Egyptian villages in Aswan, located at 24° 05′20′′ N and 32° 53′59′′ E on the eastern bank of the Nile River. It is situated approximately 900 km south of Cairo, Egypt. All owners provided informed consent before the animals were included in the study.

Twenty-four clinically healthy pregnant dromedary camels (Camelus dromedarius) with body condition scores of 3–3.5, an average body weight of 520 ± 75 kg (mean ± SD), and ages ranging from 8 to 11 years were enrolled in this study. The she-camels were pluriparous, exhibited typical clinical characteristics, and were naturally mated. Based on their parturition outcomes, the animals were classified into three groups: (i) eutocia group (EG, n = 12), She-camels that delivered calves spontaneously without human intervention, as defined by Hussein et al. (21). (ii) dystocia group (DG, n = 5), She-camels that experienced difficult deliveries requiring manual assistance (22, 23). (iii) uterine inertia group (UIG, n = 7) She-camels that delivered only after forced traction without manual corrections, according to (24). Furthermore, this data represents all cases observed and subsequently confirmed that met the inclusion criteria during the study period. Therefore, the imbalance reflects the observed birthing conditions during this period, not the result of a pre-designed distribution. The camels were maintained on a pasture-based diet, supplemented with alfalfa (Medicago sativa) when natural forage availability was limited. Fresh water was provided ad libitum throughout the study period. The first 10 days before the expected calving date, all signs of imminent parturition were closely monitored.

Placental efficiency was determined as the ratio of neonatal camel weight to placenta weight, expressed as a percentage, according to the following equation (25).

Five full-thickness tissue blocks were obtained at random from the middle zone of each placenta’s belt, rinsed in sterile saline (0.9% NaCl), and immediately fixed in 10% neutral phosphate-buffered formalin (pH 7.0). Three non-overlapping, randomly selected microscopic fields (at 200x magnification) were examined from each block, for a total of 15 fields per animal. For histological processing, specimens underwent gradual dehydration through an ethanol series (50–99%), were cleared in methyl benzoate, and were embedded in paraffin wax at 58–62 °C. Serial sections (5 μm thickness) were cut using a rotary microtome and stained with Harris hematoxylin and eosin (H&E) for routine histological evaluation. Slides were examined under high-power light microscopy (Olympus BX43F, Tokyo, Japan). Digital image acquisition was performed using an Olympus DP74 camera (Tokyo, Japan). Histomorphological examination was performed by a specialist unfamiliar with the cohorts, and the fields were re-examined after 1 week to assess the accuracy of the measurements.

Blood samples were collected within 15 min. Postpartum, venous blood samples (n = 24) were collected from all animals via jugular venipuncture into plain serum tubes. Samples were centrifuged at 3000 × g for 20 min at room temperature, after which serum was aliquoted and stored at −20 °C until analysis. Serum concentration of progesterone and estradiol 17β was quantified using a chemiluminescent immunoassay (iFlash Immunoassay Analyzer, Shenzhen Yhlo Biotech, Co., Ltd., China). Cortisol concentrations were determined using a competitive ELISA (ABC Biotech kit, Berlin, Germany). Oxidative stress markers, total antioxidant capacity (TAC) and malondialdehyde (MDA) were determined using commercial colorimetric kits (Bio Diagnostic Egypt, CAT Nos. MD2529 and TA2513, respectively). Duplicate measurements were taken for all protocols, and each protocol was performed as per the manufacturer’s guidelines. In the method validation, the inter-assay coefficient of variation (%CV) was ≤10% for estradiol-17β, ≤8% for progesterone, ≤7% for cortisol, and ≤15% for some of the oxidative stress markers (MDA and TAC). Hormonal concentrations, particularly cortisol, are likely to be influenced by the acute stress associated with childbirth. Therefore, differences were compared between groups whose blood samples were collected simultaneously.

The statistical analyses were conducted using SPSS for Windows, Version 25 (IBM Corp., Chicago, IL, United States). The normality of the data distribution was assessed using the Kolmogorov–Smirnov test; data were considered normally distributed if p > 0.05. For comparisons among the eutocia, dystocia, and uterine inertia groups a one-way ANOVA was applied according to the general linear model:

where Yij is the observed value, μ is the overall mean, Ti represents the treatment effect (delivery groups), and Eij is the random error. When ANOVA indicated significant differences, the Duncan post-hoc test was used for pairwise comparisons. Correlations between variables were evaluated using Spearman’s rank correlation coefficient (ρ), reported alongside 95% confidence intervals (CI) and corresponding p-values to convey both the strength and precision of the associations. A significance level of p < 0.05 was applied for all tests. R values are reported alongside their p-values to provide a direct measure of correlation strength.

The weight of neonatal calves and placentas, along with placental efficiency, was compared among camels experiencing eutocia (EG), dystocia (DG), and uterine inertia (UIG) in Table 1. Neonatal calves and placental weight (kg) were significantly higher (p < 0.01) in the DG group than in the EG and UIG groups. However, while placental efficiency did not differ significantly (p > 0.05) between the EG and UIG groups, it was significantly lower (p < 0.05) in the DG group than in either the EG or UIG groups.

Histomorphometric measurements of placental tissue in dromedary camels with eutocia (EG), dystocia (DG), and uterine inertia (UIG) are presented in Table 2. The syncytiotrophoblast layer thickness (μm) was significantly reduced (p < 0.05) in the DG group compared to both the EG and UIG groups. Additionally, chorionic villi length (μm), chorionic villi diameter (μm), and syncytiotrophoblast layer integrity were significantly lower (p < 0.01) in the DG group than in other deliveries. Furthermore, inflammatory cell infiltration (cells/field) was significantly higher (p < 0.01) in the DG group, while vascular density (vessels/10x field) was markedly reduced (p < 0.01) compared to the EG and UIG groups.

In the EG group, placentas showed long, slender, and well-vascularized chorionic villi (Figure 1a). The syncytiotrophoblast layer appeared thick, intact, and well-organized (Figure 1b). Furthermore, the placentas from EG displayed higher vascular density, with many more well-formed blood vessels in the villous tissue (Figure 1c). Similarly, the UIG placentas group showed well-formed chorionic villi (Figure 2a) covered by an intact, uniformly structured syncytiotrophoblast layer (Figure 2b). The villous vasculature remained well-preserved, with no significant structural abnormalities (Figure 2c). In contrast, the DG placentas showed shortened, atrophic chorionic villi (Figure 3a) and a thin, irregular syncytiotrophoblast layer with focal necrosis, degenerative changes, and detachment. Additionally, the DG group tissues showed marked inflammatory infiltration (Figure 3b) and reduced vascular density, with visible vasoconstriction and partial vessel collapse (Figure 3c).

The data presented in Table 3 revealed that placenta efficiency showed no significant association with neonatal camel weight, but placental weight demonstrated a highly significant positive correlation with neonatal camel weight (p < 0.03; r = 0.579). Additionally, neonatal camel weight was significantly correlated with both placental weight (p < 0.03; r = 0.579) and syncytiotrophoblast layer thickness (p < 0.011; r = 0.509). Furthermore, placental efficiency exhibited a significant positive correlation with key histomorphometric parameters: syncytiotrophoblast layer thickness, chorionic villi diameter, vascular density, syncytiotrophoblast layer integrity, and vascular density. In contrast, inflammatory cell infiltration showed a highly negative correlation (p < 0.019) with placental efficiency (r = −0.475).

Progesterone, estradiol 17β, and cortisol serum concentrations in dromedary camels experiencing eutocia (EG), dystocia (DG), and uterine inertia (UIG) are shown in Table 4. Progesterone concentrations were significantly elevated (p < 0.01) in the DG group compared with both the EG and UIG groups. Additionally, the UIG group showed higher progesterone concentration (p < 0.01) than the EG group. Estradiol 17β concentrations were recorded at the lowest values in the DG group compared to other groups and at the highest values in the EG (p < 0.01). Cortisol concentrations differed significantly (p < 0.01) among groups.

MDA and TAC concentrations in dromedary camels experiencing eutocia (EG), dystocia (DG), and uterine inertia (UIG) are shown in Table 5. The EG group showed the lowest (p < 0.01) MDA levels, with progressively higher levels in the DG and UIG groups. In contrast, the EG group showed the highest (p < 0.01) TAC levels, with the lowest in the DG group and intermediate in the IUG group.

The data presented in Table 6 showed that the negative correlations (p < 0.01) among Progesterone concentrations and placental efficiency (r = 0.726), syncytiotrophoblast thickness (r = 0.879), chorionic villi length (r = 0.683), vascular density (r = 0.713), and syncytiotrophoblast integrity (r = 0.655), but there was a negative correlation (p < 0.01) with inflammatory cells. However, there was a significant positive correlation (p < 0.01) among estradiol 17β placental efficiency (r = 0.512), syncytiotrophoblast thickness (r = 0.807), chorionic villi length (r = 0.651), vascular density (r = 0.620), syncytiotrophoblast integrity (r = 0.631), and vascular density (r = 0.693). Placental efficiency, chorionic villi length, syncytiotrophoblast integrity, vascular density, and syncytiotrophoblast thickness all showed negative correlations with cortisol and MDA, contrary to TAC results.

Although this study provides novel insights into placental biomarkers linked to dystocia in dromedary camels, it should be acknowledged that the small sample size and imbalance are inherent to the rarity and clinical nature of these cases. Despite these limitations, this work provides a crucial foundational description for future research. Dystocia is a significant medical and economic issue across various animal species. The Arabian camels range from 5 to 10%, compared to 15–20% of births requiring assistance in dairy cattle (38). Sheep have a higher incidence, especially in multiple pregnancies, where the rate reaches 80%, contrasting with just 5% for singleton births (39). In mare, dystocia is a critical emergency, with maternal mortality rates of up to 10% if not addressed promptly (40). Current physiological insights point to a shared pathological mechanism characterized by disruptions in maternal-fetal hormonal communication, which may lead to dystocia across different species (41).