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Current IssueEditorial BoardOnline First ArticlesArchive

Full Research Article

Anatomical and Histological Study of the Female Reproductive System (Columba oenas) during the Egg-laying Period

S
Sura Abdul Munaff Abdul Wahab1,*
1Department of Biology, College of Science, University of Baghdad, Baghdad, Iraq.

ABSTRACT

Background: In this study, the female reproductive system of Columba oenas was examined during the egg laying stage, focusing on its general structure and microscopic characteristics.

Methods: Obsessive monitoring operations were performed, as well as different parts of the egg canal, which include infundibulum, magnum, isthmus, uterus and vagina.

Result: These parts showed clear anatomical differences, each with special textile features that seem to play distinctive roles related to the growth and movement of eggs. In magnum it was found that the bulk contains clear mucous folds and many secretory glands. The isthmus had a star-shaped lumen and was lined with a false cylindrical epithelium. In the uterus, branching tube glands, rich in multiple mucous sugars are observed, which are likely to contribute to the process of cortex formation. The vaginal area showed longitudinal folds consisting of cylindrical epithelial fabric. These changes combined indicate that the reproductive system adapts structurally while laying eggs to support the needs and laying eggs.

INTRODUCTION

Birds represent a significant group of vertebrates that have garnered considerable attention from researchers due to their distinctive centralized morphological and physiological traits (Williams, 2012; Yaseen et al., 2025; M Obaid et al., 2025). Understanding the avian reproductive system is crucial for advancing knowledge of reproductive biology and improving productivity in certain domesticated bird species (Johnson, 2014; Yaseen et al., 2024; Obaid et al., 2020).
       
The common wood or stock pigeon (Columba oenas), belonging to the family Columbidae (pigeons and doves), is identifiable by its blue-grey plumage marked with black wing spots. Males typically measure 32-34 cm in body length and weigh between 303-365 g, while females weigh approximately 286-290 g (BirdLife DataZone, 2023). In Iraq, the species is prevalent in the northern and central regions, favoring habitats such as open woodlands, farmlands with scattered trees and hedgerows (Al-Mansour and Al-Zghoul, 2020).
       
The female avian reproductive system differs notably from that of most mammals. While mammals typically possess paired ovaries and uterine horns, female birds develop only a single functional ovary and oviduct (left side), as the right ovary and oviduct regress during embryonic development (Onagbesan et al., 2009; Obaid et al., 2020; Kareem et al., 2023). The avian oviduct comprises five distinct regions: infundibulum, magnum, isthmus, uterus and vagina. Each of these parts performs specialized functions during the activity of the oviduct, including the processes from reception of the egg to its laying (Sasanami et al., 2013; Altemeemi et al., 2021; Al-Khuzaay et al., 2024). The anatomical and histological characteristics of the female reproductive system in birds are influenced by physiological conditions and vary with the breeding season (van der Klein et al., 2020). During the egg-laying phase, the ovary and the oviduct undergo a major structural remodeling driven by hormonal fluctuations associated with ovulation (Hrabia et al., 2021). Similar physiological adaptations have been observed in other bird species, such as ducks and emu (Kim et al., 2016; Vijayakumar et al., 2016). Furthermore, inter-species textural differences, including Turkey and ostrich, have been documented, especially in infundibulum, magnum isthmus and uterus (Yahya et al., 2024; Hameed et al., 2025). However, detailed anatomical and tissue information on the Columba oenas oviduct during the egg-laying period is still limited compared to other pigeon species previously studied. This study aimed to investigate that of the gross and and microscopic female reproductive system in Stock Doves (Columba oenas) during the egg-laying phase. Focus was placed on the ovary and individual oviduct segments to identify morphological and histological features associated with functional specialization for egg formation in this species.

MATERIALS AND METHODS

Samples
 
This study utilized fifteen (15) adult female Stock Doves (Columba oenas) during the egg-laying period (March to May), with an average body weight range of 270-285 g. Birds were obtained from local markets and maintained under standard management conditions: Temperature (22-25oC), photoperiod (14 h light:10 h dark) and appropriate nutrition. The bird were confirmed to be in the laying phase through reproductive behavior observation and post-mortem examination of the reproductive system. The study adhered to institutional ethical standards for laboratory animal care and use.
 
Anatomical study
 
Birds were anesthetized using chloroform and humanely euthanized. After opening the abdominal cavity, the entire female reproductive system (ovary and oviduct) was carefully excised. Gross anatomical observations were recorded and photographed. Morphometric measurements were taken using a calibrated ruler and digital calipers, recording: Length of each oviduct segment (mm), Weight of each segment (g), Diameter of each segment (mm), Number of mucosal folds per segment and Height and width of mucosal folds (μm).
 
Histological study
 
Small samples (0.5 cm) were collected from the ovary and each oviduct segment (infundibulum, magnum, isthmus, uterus, vagina). Samples were fixed in 10% neutral buffered formalin for 48 hours, washed in running water, dehydrated through graded ethanol series (70%, 80%, 90%, 95%, 100%), cleared in xylene, embedded in paraffin wax and sectioned at 5 μm thickness using a rotary microtome. For general histology, the sections were stained with: Hematoxylin and Eosin, for neutral carbohydrates stained by periodic acid-schiff (PAS) and alcian blue (AB) for acidic carbohydrates.
 
Histomorphometry analysis
 
light microscope with an attached digital camera used for Sections examination. The following measurements were made using ImageJ software: Epithelial thickness (μm), mucosal fold height (μm), Mucosal fold width (μm), submucosal layer thickness (μm) and muscular layer thickness (μm).
 
Statistical analysis
 
Statistical analysis was performed by SPSS 25. For all data, means and standard deviations were obtained. Comparison between the various segments of the oviduct was performed by one-way ANOVA followed by Tukey’s test for multiple comparisons. P<0.05 was statistically significant.

RESULTS AND DISCUSSION

Gross anatomy of the female reproductive system
 
Gross examination revealed a functional left ovary and left oviduct, with the right ovary and oviduct being vestigial (Fig 1). The left ovary was located dorsally in the abdominal cavity anterior to the left kidney, appearing cluster-like with ovarian follicles at various developmental stages, ranging from small primary follicles to large mature yellow follicles.

Fig 1: Genital apparatus of a laying Columba oenas (gastrointestinal tract removed) This image shows the left reproductive system of an adult laying Columba oenas female with the gastrointestinal tract removed for anatomical clarity.


       
The oviduct consisted of five anatomically distinct segments from anterior to posterior: Infundibulum, Magnum, Isthmus, Uterus and Vagina (Fig 1). The infundibulum formed a funnel receiving the ovulated ovum; the magnum was the longest segment; the isthmus had a relatively smaller diameter; the uterus was the most dilated; and the short vagina opened into the cloaca.
       
The gross morphometric measurements of the different segments of the oviduct (Table 1). The results showed significant differences (P<0.05) in the measure-ments among the various segments. The magnum was the longest segment, with an average length of 41.24±0.55 mm, while the infundibulum was the shortest, with an average length of 22.43±0.72 mm. The uterus was the heaviest segment, weighing 455.8±0.83 g, whereas the infundibulum was the lightest at 67.8±0.79 g. Regarding diameter, the magnum had the largest average diameter at 425.43±0.35 mm, while the infundibulum had the smallest at 50.63±0.48 mm.

Table 1: Gross morphometric measurements of oviduct segments in Columba oenas during egg-laying.



Histology of the ovary
 
Histologically the ovary is composed of an outer cortex and an inner medulla that is vascular (Fig 2A). The cortex contained follicles at various stages: Primary follicles with a single layer of granulosa cells and secondary follicles with multilayered granulosa cells (Fig 2B). Mature follicles exhibited a single layer of granulosa cells, a vascular theca interna and a fibrous theca externa (Fig 2C). The medulla contained blood vessels, connective tissue and nerves (Fig 2D).

Fig 2: A photomicrograph of female Columba oenas ovary.


 
Histology of the oviduct
 
Infundibulum
 
The infundibular wall comprised of four layers: Tunica mucosa, T. submucosa, T. muscularis and T. serosa (Fig 3A). The mucosa featured finger-like folds (Fig 3B) lined by simple columnar epithelium with ciliated and non-ciliated cells (Fig 3C). The lamina propria had scattered lymphoid nodules and mucous glands (Fig 3D). The muscularis was relatively thin, with inner circular and outer longitudinal layers.

Fig 3: Photomicrographs of the infundibulum part of the oviduct of adult female Columba oenas showing.


       
Table 2 presents the histological measurements of the oviduct. The mean epithelial thickness of the infundibulum was 18.45±0.33 µm, the submucosal thickness was 28.71±0.47 µm and the muscular layer thickness was 65.38±0.56 µm. The mean height of the mucosal folds was 310.25±0.82 µm and their width was 82.46±0.63 µm.

Table 2: Histomorphometric measurements (mm) of oviduct segments in Columba oenas during egg-laying.


 
Magnum
 
The magnum wall showed four distinct layers (Fig 4A). The mucosa exhibited long, broad, leaf-like folds (Fig 4B). The lamina propria contained numerous PAS-positive secretory glands (Fig 4C). The surface epithelium was tall columnar with ciliated and non-ciliated cells (Fig 4D). The muscularis was thicker than in the infundibulum.

Fig 4: Photomicrographs of the magnum region of the adult female Columba oenas oviduct.


       
According to the histological measurements (Table 2), the mean epithelial thickness of the magnum was 32.63±0.42 µm, which was significantly greater (P<0.05) than that of the infundibulum. The mean thickness of the submucosal layer was 175.34±0.75 µm and the muscular layer measured 125.82±0.68 µm. The mean height of the mucosal folds was 650.53±0.94 µm and their width was 195.76±0.85 µm, both of which were significantly greater (P<0.05) than those in the infundibulum.
 
Isthmus
 
The isthmus displayed a star-shaped lumen (Fig 5A), pseudostratified columnar epithelium (Fig 5B) and moderately PAS-positive secretory glands (Fig 5C). Blood vessels were observed in the submucosa (Fig 5D).

Fig 5: Photomicrographs of the isthmus part of the oviduct in adult female Columba oenas showing.


       
According to the histological measurements (Table 2), the mean epithelial thickness of the isthmus was 25.19±0.38 µm, the submucosal layer thickness was 90.54±0.63 µm and the muscular layer thickness was 130.47±0.72 µm. The mean height of the mucosal folds was 410.36±0.86 µm and their width was 120.83±0.74 µm.
 
Uterus
 
The uterine mucosa showed branched, complex folds (Fig 6A) and abundant branched tubular glands positive for PAS and AB (Fig 6B, C). The epithelium was ciliated (Fig 6D). The submucosa was highly vascularized.

Fig 6: Photomicrographs of the uterus part of adult female Columba oenas oviduct showing.


       
According to the histological measurements (Table 2), the mean epithelial thickness of the uterus was 20.81±0.35 µm and the submucosal layer thickness was 250.65±0.82 µm, which was significantly the highest (P<0.05) among all oviduct segments. The muscular layer measured 180.37±0.77 µm. The mean height of the mucosal folds was 480.72±0.91 µm and their width was 170.58±0.81 µm.

Vagina
 
The vaginal mucosa featured longitudinal folds (Fig 7A) lined by simple/pseudostratified columnar epithelium (Fig 7B). Branched tubular glands opened into the lumen (Fig 7C) and showed strong AB-positivity with dark blue acidic mucin granules (Fig 7D). The muscularis was exceptionally thick.

Fig 7: Photomicrographs of the vaginal part of adult female Columba oenas oviduct showing.


       
According to the histological measurements (Table 2), the mean epithelial thickness of the vagina was 28.35±0.39 µm, the submucosal layer thickness was 45.28±0.54 µm and the muscular layer thickness was 195.43±0.79 µm, which was significantly the highest (P<0.05) among all oviduct segments. The mean height of the mucosal folds was 380.45±0.84 µm and their width was 110.27±0.71 µm.
       
The results of the current study showed that the female reproductive system in Columba oenas consists solely of the left ovary and oviduct, while the right side is regressed. This feature is consistent with the findings of King and McLelland (1984), who noted that most bird species possess only a functional left ovary and oviduct, except for some birds such as falcons, which may retain a partially developed right reproductive tract. In a rare case, Kinsky (1971) reported the presence of paired ovaries in the kiwi (Apteryx). The stockdove (Columba oenas) is widespread in western and northwestern Iraq (Salim et al., 2012). The anatomical measurements in our study align with those of Al-Dokhiel (2011) on the domestic pigeon (Columba livia), particularly in terms of the relative order of lengths and diameters of the oviductal segments, although absolute values differ due to species-specific variation. The study observed that the magnum is the longest segment of the oviduct (representing 48.7% of the total length), while the uterus has the largest diameter. This agrees with Carreiro et al. (2021), who also found such similarities in domestic pigeons. These differences are associated with different functions of adaptation from each segment’s need to perform: the magnum for its secretory function (albumen) needs a large secretory surface, while the uterus needs to be able to accommodate the egg through shell formation (Chousalkar et al., 2010; Abd El-Rahmana et al., 2024; Al-Maliki et al., 2025).
       
The ovary at time of ovulation was histologically characterized by follicles at different stages of development in the outer cortex, indicative of continuous and synchronous ovarian function. This fits in accordance with Johnson (2014), wherein the avian ovary was characterized by staged follicular growth The presented results agree with Johnson (2014), who described ache to for hierarchically staged follicular growth by the avian ovary. The existence of primordial, primary and secondary and mature follicles simultaneously is an indication of the cyclic nature of pigeon ovarian activity. Onagbesan et al. (2009) have also reported that the follicular dynamics in birds enables egg production for continuous periods. A recent transcriptome study by Zhang et al. (2023) in domestic pigeons. Also, during the different developmental stages of the follicles, noticeable patterns of gene expression specific to follicular development stages were reported. Germinal vesicle and mature follicles displayed deposition vacuoles in the ooplasm yolk, like the findings of Rahman et al. (2019) in Japanese quail. The yolk nourishes the growing embryo. Stephens and Johnson (2019) emphasized the crucial role of egg yolk accumulation in determining egg quality and fertility.
       
The infundibulum featured branched finger-like mucosal folds composed of ciliated columnar epithelium. According to Bakst and Akuffo (2019) this structure is conducive to interception of the ovulated oocyte. Interestingly, lymphoid nodules were seen in the lamina propria, corroborating Madekurozwa (2016) who reported innate defense protection in the reproductive tract. The sperm storage tubules are also present in the infundibulum, as has been described by Martínez et al. (2017) that carry out sperm storage over weeks to fertilize multiple oocytes.
       
The magnum exhibited long, leaf-like mucosal folds and highly branched tubular glands in the lamina propria, which were consistent with those described by El-Sayed et al. (2021). Intense PAS-positive reactions were observed, which presumably indicate the secretion of glycoproteins involved in egg white formation) are responsible for the secretion of 40-50% of egg white proteins such as albumin, ovomucoid, lysozyme and other such, antimicrobial and antiviral proteins (Rahman and Sasanami, 2020). The longer magnum and its thick glandular organization might be because the major secretory function is developed, because under this part, the egg is kept for 4-5 hr (Sasanami et al., 2013; Razooki et al., 2025; Jasim et al., 2025).
       
The isthmus had wide mucosal folds and a stellate lumen lined by pseudostratified columnar epithelium and PAS-positive secretory glands. These characteristics are consistent with those of Hassan et al. (2019) and these generated isthmus compartments have been reported to include shell membrane-secreting cells in the epithelium of the isthmus (Razooki et al., 2019). The glands are important to produce fibrous proteins that contribute to inner and outer shell membranes. As reported by Chousalkar et al. (2010), such membranes are composed of collagen, keratins and proteoglycans, which provide substrate for the calcium carbonate deposition. Our findings corroborate that the isthmus is involved in initial calcium salt deposition, as described by Chen et al. (2018); Mirhish and Nasif, (2013).
       
The uterus showed deep branched mucosal folds, ciliated columnar epithelium and branched tubular glands with strong PAS and Alcian blue staining. This histological pattern reveals the complex functioning of the uterus related to shell formation and agrees with Gómez et al. (2019). Uterine glands play a crucial role in the transport of calcium and carbonate ions necessary for the calcium carbonate shell, which represents 95% of the total shell weight. Reynolds et al. (2017) drew attention to the relationship between calcium metabolism and avian reproduction, where dietary sources and skeletal structures provide the necessary calcium. The uterus is another source of pigments to the shell, which may explain the presence of glands that produce both neutral and acidic mucins. The results correspond with those of Carreiro et al. (2021) and Ibrahim et al. (2015), who stressed the multifunctional role of uterine glands in pigeons.
       
The results of the study revealed deep longitudinal mucosal folds, a thick muscularis, particularly the longitudinal layer and branched glands positive to PAS and AB in the vagina. The longitudinal folds in the station increase the area and help with lubrication and the smooth passage of the egg. Analogous structures were described by Gómez et al. (2019), who emphasized their protective and secretory capacities. The thick muscular layer, especially the longitudinal muscle layer, allows forcing strong peristaltic contractions, which are essential for the expulsion of egg. Wang et al. (2014) reported the importance of the vaginal smooth muscles involving in the transportation of the egg from the ovary to the cloaca. Moreover, the vagina is involved in spermicide and immunity. The vagnial environment is known to serve as a selective barrier for healthy sperm before they get to the sperm storage tubules (Bakst and Akuffo, 2019). Positive PAS- and Alcian blue-stained glands indicate the production of mucus performing a role both mechanical and immunologic (Gómez et al. 2019; Razooki et al., 2020). The vagina also contributes to the immune system’s selection of sperm as only healthy sperm through mechanisms were described by Bakst and Akuffo (2019) can reach storage tubules of the infundibulum, this results in quality (Gupta and Bakst, 1993). The intense PAS and Alcian blue reactivity of the glands indicates that they secrete mixed mucins, as described by Gómez et al. (2019) who reported on its protective mechanical and immunological role in the process of egg laying.
       
Histological features were significantly different among oviductal segments in the present study (Table 2), which reflects the different functions of the segments in egg production. These results are consistent with Al-Mansour and Al-Zghoul (2020), who highlighted the relationship between the histological, physiological and biological function of the oviduct in theEurasian collared dove. Epithelial thickness was greatest in the uterus (45.31±0.53 µm), followed by the magnum (41.24±0.55 µm), correlating with their secretory activity. Mucosal folds were longest in the uterus (1760.4±0.41 µm), increasing surface area for ion exchange during shell formation. (El-Sayed et al. 2021; Salam et al., 2025; Abass et al., 2025) linked fold length with secretory intensity. Gland diameter was largest in the magnum (425.43±0.35 µm), followed by the uterus (360.77±0.75 µm), consistent with their roles in secreting proteins and calcium, respectively.
       
Hassan et al. (2019) also described that hypertrophy of glandular cells observed in these segments is influenced by increased estrogen and progesterone at the time of egg-laying. The muscular layer was largest in the vagina and the uterus, the longitudinal muscle (455.8±0.83 and 420.5±0.59 µm, respectively), supporting the crucial role in egg transpor. Wang et al. (2014) have pointed out the requirement of powerful smooth muscles for egg-propulsion, especially after the completion of the shell.
       
Increased estrogen levels induce the development of the epithelial gland, progesterone is responsible for secretory activity and growth of the smooth muscle. Nakamura et al. (2021) highlighted the effect of progesterone on glandular development, notably in the magnum and uterus (Williams, 2012; van der Klein et al., 2020). Prolactin is also involved in reproductive activities such as follicular development and glandular function (Hrabia et al. 2021) and further demonstrated by (Smith et al., 2020; Ghiath et al., 2025). The expansion and increasing complexity of the gland during oviposition reflects hormonal response as described by Patel et al. (2010) who reported histological and biochemical ovarian alterations of domestic pigeons due to reproduction.
       
The female reproductive system in Columba oenas: Anatomical, histological and immunohistochemical study the anatomical and histological structures of the female reproductive system in Columba oenas were found to be like those in other birds, but with some species-specific character. The magnum accounts for a large amount in the oviduct length and then in domesticated chicken as observed by Nabil et al. (2022), indicating its functional specilization. The vaginal muscle layer in pigeons is thicker than that in quail, similar to that found in larger birds (Al-Dokhiel, 2011; Hmeed et al., 2025; Al-Mashhadani et al., 2024). Comparison with Al-Mansour and Al-Zghoul (2020) on the Eurasian collared dove revealed closely resembling structure of the oviduct with some differences in the size of mucosal folds and thickness of musculature, presumably attributable to phylogenetic distance. However, other research on phylogenetically more distant birds (e.g., Madekurozwa, 2016, on ostriches) show more pronounced structural dissimilarities, especially in sperm storage tubule layout and gland distribution, which suggest greater evolutionary divergent.

CONCLUSION AND RECOMMENDATION

1. The female reproductive tract of Columba oenas is clearly adapted for egg-laying and provides accounts of the histological structure that must ensure the specialized functions of each oviductal parts during the egg formation.
2. Histological examination demonstrated that there were significant differences of the type of epithelium, structure of mucosal folds, glands and muscle thickness between segments of the oviduct, which are conducive to their supporting crucial role in secretion, transport and calcification.
3. The study recommends comparative evaluation of the reproductive tract in different reproductive stages and correlating these changes with hormonal fluctuations (estrogen, progesterone, prolactin).
4. The use of advanced techniques such as electron microscopy, immunohistochemistry and 3D imaging is encouraged to explore microstructural and molecular mechanisms governing egg formation and reproductive function.
 
Novelty statement
 
Despite the extensive research on the reproductive systems of domestic avian species, there remains a notable scarcity of detailed anatomical and histological data regarding the female reproductive tract of wild pigeons, particularly the Stock Dove (Columba oenas) during the egg-laying period. To our knowledge, this is the first comprehensive study to document the gross morphology and microanatomy of the ovary and oviduct in Columba oenas in correlation with its reproductive cycle. This work provides novel insights into the segmental structure, glandular distribution, epithelial variations and functional specialization of the oviduct during peak reproductive activity. The findings contribute significantly to the comparative anatomy of wild columbids and offer a valuable baseline for future ecological, physiological and conservation-oriented studies.
 
Data availability statement
 
All data generated or analyzed during this study are included in the published article. Additional supporting materials are available from the corresponding author upon reasonable request.

CONFLICT OF INTEREST

The author warrants that there is no conflict of interest in the manuscript.

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    Anatomical and Histological Study of the Female Reproductive System (Columba oenas) during the Egg-laying Period

    S
    Sura Abdul Munaff Abdul Wahab1,*
    1Department of Biology, College of Science, University of Baghdad, Baghdad, Iraq.

    ABSTRACT

    Background: In this study, the female reproductive system of Columba oenas was examined during the egg laying stage, focusing on its general structure and microscopic characteristics.

    Methods: Obsessive monitoring operations were performed, as well as different parts of the egg canal, which include infundibulum, magnum, isthmus, uterus and vagina.

    Result: These parts showed clear anatomical differences, each with special textile features that seem to play distinctive roles related to the growth and movement of eggs. In magnum it was found that the bulk contains clear mucous folds and many secretory glands. The isthmus had a star-shaped lumen and was lined with a false cylindrical epithelium. In the uterus, branching tube glands, rich in multiple mucous sugars are observed, which are likely to contribute to the process of cortex formation. The vaginal area showed longitudinal folds consisting of cylindrical epithelial fabric. These changes combined indicate that the reproductive system adapts structurally while laying eggs to support the needs and laying eggs.

    INTRODUCTION

    Birds represent a significant group of vertebrates that have garnered considerable attention from researchers due to their distinctive centralized morphological and physiological traits (Williams, 2012; Yaseen et al., 2025; M Obaid et al., 2025). Understanding the avian reproductive system is crucial for advancing knowledge of reproductive biology and improving productivity in certain domesticated bird species (Johnson, 2014; Yaseen et al., 2024; Obaid et al., 2020).
           
    The common wood or stock pigeon (Columba oenas), belonging to the family Columbidae (pigeons and doves), is identifiable by its blue-grey plumage marked with black wing spots. Males typically measure 32-34 cm in body length and weigh between 303-365 g, while females weigh approximately 286-290 g (BirdLife DataZone, 2023). In Iraq, the species is prevalent in the northern and central regions, favoring habitats such as open woodlands, farmlands with scattered trees and hedgerows (Al-Mansour and Al-Zghoul, 2020).
           
    The female avian reproductive system differs notably from that of most mammals. While mammals typically possess paired ovaries and uterine horns, female birds develop only a single functional ovary and oviduct (left side), as the right ovary and oviduct regress during embryonic development (Onagbesan et al., 2009; Obaid et al., 2020; Kareem et al., 2023). The avian oviduct comprises five distinct regions: infundibulum, magnum, isthmus, uterus and vagina. Each of these parts performs specialized functions during the activity of the oviduct, including the processes from reception of the egg to its laying (Sasanami et al., 2013; Altemeemi et al., 2021; Al-Khuzaay et al., 2024). The anatomical and histological characteristics of the female reproductive system in birds are influenced by physiological conditions and vary with the breeding season (van der Klein et al., 2020). During the egg-laying phase, the ovary and the oviduct undergo a major structural remodeling driven by hormonal fluctuations associated with ovulation (Hrabia et al., 2021). Similar physiological adaptations have been observed in other bird species, such as ducks and emu (Kim et al., 2016; Vijayakumar et al., 2016). Furthermore, inter-species textural differences, including Turkey and ostrich, have been documented, especially in infundibulum, magnum isthmus and uterus (Yahya et al., 2024; Hameed et al., 2025). However, detailed anatomical and tissue information on the Columba oenas oviduct during the egg-laying period is still limited compared to other pigeon species previously studied. This study aimed to investigate that of the gross and and microscopic female reproductive system in Stock Doves (Columba oenas) during the egg-laying phase. Focus was placed on the ovary and individual oviduct segments to identify morphological and histological features associated with functional specialization for egg formation in this species.

    MATERIALS AND METHODS

    Samples
     
    This study utilized fifteen (15) adult female Stock Doves (Columba oenas) during the egg-laying period (March to May), with an average body weight range of 270-285 g. Birds were obtained from local markets and maintained under standard management conditions: Temperature (22-25oC), photoperiod (14 h light:10 h dark) and appropriate nutrition. The bird were confirmed to be in the laying phase through reproductive behavior observation and post-mortem examination of the reproductive system. The study adhered to institutional ethical standards for laboratory animal care and use.
     
    Anatomical study
     
    Birds were anesthetized using chloroform and humanely euthanized. After opening the abdominal cavity, the entire female reproductive system (ovary and oviduct) was carefully excised. Gross anatomical observations were recorded and photographed. Morphometric measurements were taken using a calibrated ruler and digital calipers, recording: Length of each oviduct segment (mm), Weight of each segment (g), Diameter of each segment (mm), Number of mucosal folds per segment and Height and width of mucosal folds (μm).
     
    Histological study
     
    Small samples (0.5 cm) were collected from the ovary and each oviduct segment (infundibulum, magnum, isthmus, uterus, vagina). Samples were fixed in 10% neutral buffered formalin for 48 hours, washed in running water, dehydrated through graded ethanol series (70%, 80%, 90%, 95%, 100%), cleared in xylene, embedded in paraffin wax and sectioned at 5 μm thickness using a rotary microtome. For general histology, the sections were stained with: Hematoxylin and Eosin, for neutral carbohydrates stained by periodic acid-schiff (PAS) and alcian blue (AB) for acidic carbohydrates.
     
    Histomorphometry analysis
     
    light microscope with an attached digital camera used for Sections examination. The following measurements were made using ImageJ software: Epithelial thickness (μm), mucosal fold height (μm), Mucosal fold width (μm), submucosal layer thickness (μm) and muscular layer thickness (μm).
     
    Statistical analysis
     
    Statistical analysis was performed by SPSS 25. For all data, means and standard deviations were obtained. Comparison between the various segments of the oviduct was performed by one-way ANOVA followed by Tukey’s test for multiple comparisons. P<0.05 was statistically significant.

    RESULTS AND DISCUSSION

    Gross anatomy of the female reproductive system
     
    Gross examination revealed a functional left ovary and left oviduct, with the right ovary and oviduct being vestigial (Fig 1). The left ovary was located dorsally in the abdominal cavity anterior to the left kidney, appearing cluster-like with ovarian follicles at various developmental stages, ranging from small primary follicles to large mature yellow follicles.

    Fig 1: Genital apparatus of a laying Columba oenas (gastrointestinal tract removed) This image shows the left reproductive system of an adult laying Columba oenas female with the gastrointestinal tract removed for anatomical clarity.


           
    The oviduct consisted of five anatomically distinct segments from anterior to posterior: Infundibulum, Magnum, Isthmus, Uterus and Vagina (Fig 1). The infundibulum formed a funnel receiving the ovulated ovum; the magnum was the longest segment; the isthmus had a relatively smaller diameter; the uterus was the most dilated; and the short vagina opened into the cloaca.
           
    The gross morphometric measurements of the different segments of the oviduct (Table 1). The results showed significant differences (P<0.05) in the measure-ments among the various segments. The magnum was the longest segment, with an average length of 41.24±0.55 mm, while the infundibulum was the shortest, with an average length of 22.43±0.72 mm. The uterus was the heaviest segment, weighing 455.8±0.83 g, whereas the infundibulum was the lightest at 67.8±0.79 g. Regarding diameter, the magnum had the largest average diameter at 425.43±0.35 mm, while the infundibulum had the smallest at 50.63±0.48 mm.

    Table 1: Gross morphometric measurements of oviduct segments in Columba oenas during egg-laying.



    Histology of the ovary
     
    Histologically the ovary is composed of an outer cortex and an inner medulla that is vascular (Fig 2A). The cortex contained follicles at various stages: Primary follicles with a single layer of granulosa cells and secondary follicles with multilayered granulosa cells (Fig 2B). Mature follicles exhibited a single layer of granulosa cells, a vascular theca interna and a fibrous theca externa (Fig 2C). The medulla contained blood vessels, connective tissue and nerves (Fig 2D).

    Fig 2: A photomicrograph of female Columba oenas ovary.


     
    Histology of the oviduct
     
    Infundibulum
     
    The infundibular wall comprised of four layers: Tunica mucosa, T. submucosa, T. muscularis and T. serosa (Fig 3A). The mucosa featured finger-like folds (Fig 3B) lined by simple columnar epithelium with ciliated and non-ciliated cells (Fig 3C). The lamina propria had scattered lymphoid nodules and mucous glands (Fig 3D). The muscularis was relatively thin, with inner circular and outer longitudinal layers.

    Fig 3: Photomicrographs of the infundibulum part of the oviduct of adult female Columba oenas showing.


           
    Table 2 presents the histological measurements of the oviduct. The mean epithelial thickness of the infundibulum was 18.45±0.33 µm, the submucosal thickness was 28.71±0.47 µm and the muscular layer thickness was 65.38±0.56 µm. The mean height of the mucosal folds was 310.25±0.82 µm and their width was 82.46±0.63 µm.

    Table 2: Histomorphometric measurements (mm) of oviduct segments in Columba oenas during egg-laying.


     
    Magnum
     
    The magnum wall showed four distinct layers (Fig 4A). The mucosa exhibited long, broad, leaf-like folds (Fig 4B). The lamina propria contained numerous PAS-positive secretory glands (Fig 4C). The surface epithelium was tall columnar with ciliated and non-ciliated cells (Fig 4D). The muscularis was thicker than in the infundibulum.

    Fig 4: Photomicrographs of the magnum region of the adult female Columba oenas oviduct.


           
    According to the histological measurements (Table 2), the mean epithelial thickness of the magnum was 32.63±0.42 µm, which was significantly greater (P<0.05) than that of the infundibulum. The mean thickness of the submucosal layer was 175.34±0.75 µm and the muscular layer measured 125.82±0.68 µm. The mean height of the mucosal folds was 650.53±0.94 µm and their width was 195.76±0.85 µm, both of which were significantly greater (P<0.05) than those in the infundibulum.
     
    Isthmus
     
    The isthmus displayed a star-shaped lumen (Fig 5A), pseudostratified columnar epithelium (Fig 5B) and moderately PAS-positive secretory glands (Fig 5C). Blood vessels were observed in the submucosa (Fig 5D).

    Fig 5: Photomicrographs of the isthmus part of the oviduct in adult female Columba oenas showing.


           
    According to the histological measurements (Table 2), the mean epithelial thickness of the isthmus was 25.19±0.38 µm, the submucosal layer thickness was 90.54±0.63 µm and the muscular layer thickness was 130.47±0.72 µm. The mean height of the mucosal folds was 410.36±0.86 µm and their width was 120.83±0.74 µm.
     
    Uterus
     
    The uterine mucosa showed branched, complex folds (Fig 6A) and abundant branched tubular glands positive for PAS and AB (Fig 6B, C). The epithelium was ciliated (Fig 6D). The submucosa was highly vascularized.

    Fig 6: Photomicrographs of the uterus part of adult female Columba oenas oviduct showing.


           
    According to the histological measurements (Table 2), the mean epithelial thickness of the uterus was 20.81±0.35 µm and the submucosal layer thickness was 250.65±0.82 µm, which was significantly the highest (P<0.05) among all oviduct segments. The muscular layer measured 180.37±0.77 µm. The mean height of the mucosal folds was 480.72±0.91 µm and their width was 170.58±0.81 µm.

    Vagina
     
    The vaginal mucosa featured longitudinal folds (Fig 7A) lined by simple/pseudostratified columnar epithelium (Fig 7B). Branched tubular glands opened into the lumen (Fig 7C) and showed strong AB-positivity with dark blue acidic mucin granules (Fig 7D). The muscularis was exceptionally thick.

    Fig 7: Photomicrographs of the vaginal part of adult female Columba oenas oviduct showing.


           
    According to the histological measurements (Table 2), the mean epithelial thickness of the vagina was 28.35±0.39 µm, the submucosal layer thickness was 45.28±0.54 µm and the muscular layer thickness was 195.43±0.79 µm, which was significantly the highest (P<0.05) among all oviduct segments. The mean height of the mucosal folds was 380.45±0.84 µm and their width was 110.27±0.71 µm.
           
    The results of the current study showed that the female reproductive system in Columba oenas consists solely of the left ovary and oviduct, while the right side is regressed. This feature is consistent with the findings of King and McLelland (1984), who noted that most bird species possess only a functional left ovary and oviduct, except for some birds such as falcons, which may retain a partially developed right reproductive tract. In a rare case, Kinsky (1971) reported the presence of paired ovaries in the kiwi (Apteryx). The stockdove (Columba oenas) is widespread in western and northwestern Iraq (Salim et al., 2012). The anatomical measurements in our study align with those of Al-Dokhiel (2011) on the domestic pigeon (Columba livia), particularly in terms of the relative order of lengths and diameters of the oviductal segments, although absolute values differ due to species-specific variation. The study observed that the magnum is the longest segment of the oviduct (representing 48.7% of the total length), while the uterus has the largest diameter. This agrees with Carreiro et al. (2021), who also found such similarities in domestic pigeons. These differences are associated with different functions of adaptation from each segment’s need to perform: the magnum for its secretory function (albumen) needs a large secretory surface, while the uterus needs to be able to accommodate the egg through shell formation (Chousalkar et al., 2010; Abd El-Rahmana et al., 2024; Al-Maliki et al., 2025).
           
    The ovary at time of ovulation was histologically characterized by follicles at different stages of development in the outer cortex, indicative of continuous and synchronous ovarian function. This fits in accordance with Johnson (2014), wherein the avian ovary was characterized by staged follicular growth The presented results agree with Johnson (2014), who described ache to for hierarchically staged follicular growth by the avian ovary. The existence of primordial, primary and secondary and mature follicles simultaneously is an indication of the cyclic nature of pigeon ovarian activity. Onagbesan et al. (2009) have also reported that the follicular dynamics in birds enables egg production for continuous periods. A recent transcriptome study by Zhang et al. (2023) in domestic pigeons. Also, during the different developmental stages of the follicles, noticeable patterns of gene expression specific to follicular development stages were reported. Germinal vesicle and mature follicles displayed deposition vacuoles in the ooplasm yolk, like the findings of Rahman et al. (2019) in Japanese quail. The yolk nourishes the growing embryo. Stephens and Johnson (2019) emphasized the crucial role of egg yolk accumulation in determining egg quality and fertility.
           
    The infundibulum featured branched finger-like mucosal folds composed of ciliated columnar epithelium. According to Bakst and Akuffo (2019) this structure is conducive to interception of the ovulated oocyte. Interestingly, lymphoid nodules were seen in the lamina propria, corroborating Madekurozwa (2016) who reported innate defense protection in the reproductive tract. The sperm storage tubules are also present in the infundibulum, as has been described by Martínez et al. (2017) that carry out sperm storage over weeks to fertilize multiple oocytes.
           
    The magnum exhibited long, leaf-like mucosal folds and highly branched tubular glands in the lamina propria, which were consistent with those described by El-Sayed et al. (2021). Intense PAS-positive reactions were observed, which presumably indicate the secretion of glycoproteins involved in egg white formation) are responsible for the secretion of 40-50% of egg white proteins such as albumin, ovomucoid, lysozyme and other such, antimicrobial and antiviral proteins (Rahman and Sasanami, 2020). The longer magnum and its thick glandular organization might be because the major secretory function is developed, because under this part, the egg is kept for 4-5 hr (Sasanami et al., 2013; Razooki et al., 2025; Jasim et al., 2025).
           
    The isthmus had wide mucosal folds and a stellate lumen lined by pseudostratified columnar epithelium and PAS-positive secretory glands. These characteristics are consistent with those of Hassan et al. (2019) and these generated isthmus compartments have been reported to include shell membrane-secreting cells in the epithelium of the isthmus (Razooki et al., 2019). The glands are important to produce fibrous proteins that contribute to inner and outer shell membranes. As reported by Chousalkar et al. (2010), such membranes are composed of collagen, keratins and proteoglycans, which provide substrate for the calcium carbonate deposition. Our findings corroborate that the isthmus is involved in initial calcium salt deposition, as described by Chen et al. (2018); Mirhish and Nasif, (2013).
           
    The uterus showed deep branched mucosal folds, ciliated columnar epithelium and branched tubular glands with strong PAS and Alcian blue staining. This histological pattern reveals the complex functioning of the uterus related to shell formation and agrees with Gómez et al. (2019). Uterine glands play a crucial role in the transport of calcium and carbonate ions necessary for the calcium carbonate shell, which represents 95% of the total shell weight. Reynolds et al. (2017) drew attention to the relationship between calcium metabolism and avian reproduction, where dietary sources and skeletal structures provide the necessary calcium. The uterus is another source of pigments to the shell, which may explain the presence of glands that produce both neutral and acidic mucins. The results correspond with those of Carreiro et al. (2021) and Ibrahim et al. (2015), who stressed the multifunctional role of uterine glands in pigeons.
           
    The results of the study revealed deep longitudinal mucosal folds, a thick muscularis, particularly the longitudinal layer and branched glands positive to PAS and AB in the vagina. The longitudinal folds in the station increase the area and help with lubrication and the smooth passage of the egg. Analogous structures were described by Gómez et al. (2019), who emphasized their protective and secretory capacities. The thick muscular layer, especially the longitudinal muscle layer, allows forcing strong peristaltic contractions, which are essential for the expulsion of egg. Wang et al. (2014) reported the importance of the vaginal smooth muscles involving in the transportation of the egg from the ovary to the cloaca. Moreover, the vagina is involved in spermicide and immunity. The vagnial environment is known to serve as a selective barrier for healthy sperm before they get to the sperm storage tubules (Bakst and Akuffo, 2019). Positive PAS- and Alcian blue-stained glands indicate the production of mucus performing a role both mechanical and immunologic (Gómez et al. 2019; Razooki et al., 2020). The vagina also contributes to the immune system’s selection of sperm as only healthy sperm through mechanisms were described by Bakst and Akuffo (2019) can reach storage tubules of the infundibulum, this results in quality (Gupta and Bakst, 1993). The intense PAS and Alcian blue reactivity of the glands indicates that they secrete mixed mucins, as described by Gómez et al. (2019) who reported on its protective mechanical and immunological role in the process of egg laying.
           
    Histological features were significantly different among oviductal segments in the present study (Table 2), which reflects the different functions of the segments in egg production. These results are consistent with Al-Mansour and Al-Zghoul (2020), who highlighted the relationship between the histological, physiological and biological function of the oviduct in theEurasian collared dove. Epithelial thickness was greatest in the uterus (45.31±0.53 µm), followed by the magnum (41.24±0.55 µm), correlating with their secretory activity. Mucosal folds were longest in the uterus (1760.4±0.41 µm), increasing surface area for ion exchange during shell formation. (El-Sayed et al. 2021; Salam et al., 2025; Abass et al., 2025) linked fold length with secretory intensity. Gland diameter was largest in the magnum (425.43±0.35 µm), followed by the uterus (360.77±0.75 µm), consistent with their roles in secreting proteins and calcium, respectively.
           
    Hassan et al. (2019) also described that hypertrophy of glandular cells observed in these segments is influenced by increased estrogen and progesterone at the time of egg-laying. The muscular layer was largest in the vagina and the uterus, the longitudinal muscle (455.8±0.83 and 420.5±0.59 µm, respectively), supporting the crucial role in egg transpor. Wang et al. (2014) have pointed out the requirement of powerful smooth muscles for egg-propulsion, especially after the completion of the shell.
           
    Increased estrogen levels induce the development of the epithelial gland, progesterone is responsible for secretory activity and growth of the smooth muscle. Nakamura et al. (2021) highlighted the effect of progesterone on glandular development, notably in the magnum and uterus (Williams, 2012; van der Klein et al., 2020). Prolactin is also involved in reproductive activities such as follicular development and glandular function (Hrabia et al. 2021) and further demonstrated by (Smith et al., 2020; Ghiath et al., 2025). The expansion and increasing complexity of the gland during oviposition reflects hormonal response as described by Patel et al. (2010) who reported histological and biochemical ovarian alterations of domestic pigeons due to reproduction.
           
    The female reproductive system in Columba oenas: Anatomical, histological and immunohistochemical study the anatomical and histological structures of the female reproductive system in Columba oenas were found to be like those in other birds, but with some species-specific character. The magnum accounts for a large amount in the oviduct length and then in domesticated chicken as observed by Nabil et al. (2022), indicating its functional specilization. The vaginal muscle layer in pigeons is thicker than that in quail, similar to that found in larger birds (Al-Dokhiel, 2011; Hmeed et al., 2025; Al-Mashhadani et al., 2024). Comparison with Al-Mansour and Al-Zghoul (2020) on the Eurasian collared dove revealed closely resembling structure of the oviduct with some differences in the size of mucosal folds and thickness of musculature, presumably attributable to phylogenetic distance. However, other research on phylogenetically more distant birds (e.g., Madekurozwa, 2016, on ostriches) show more pronounced structural dissimilarities, especially in sperm storage tubule layout and gland distribution, which suggest greater evolutionary divergent.

    CONCLUSION AND RECOMMENDATION

    1. The female reproductive tract of Columba oenas is clearly adapted for egg-laying and provides accounts of the histological structure that must ensure the specialized functions of each oviductal parts during the egg formation.
    2. Histological examination demonstrated that there were significant differences of the type of epithelium, structure of mucosal folds, glands and muscle thickness between segments of the oviduct, which are conducive to their supporting crucial role in secretion, transport and calcification.
    3. The study recommends comparative evaluation of the reproductive tract in different reproductive stages and correlating these changes with hormonal fluctuations (estrogen, progesterone, prolactin).
    4. The use of advanced techniques such as electron microscopy, immunohistochemistry and 3D imaging is encouraged to explore microstructural and molecular mechanisms governing egg formation and reproductive function.
     
    Novelty statement
     
    Despite the extensive research on the reproductive systems of domestic avian species, there remains a notable scarcity of detailed anatomical and histological data regarding the female reproductive tract of wild pigeons, particularly the Stock Dove (Columba oenas) during the egg-laying period. To our knowledge, this is the first comprehensive study to document the gross morphology and microanatomy of the ovary and oviduct in Columba oenas in correlation with its reproductive cycle. This work provides novel insights into the segmental structure, glandular distribution, epithelial variations and functional specialization of the oviduct during peak reproductive activity. The findings contribute significantly to the comparative anatomy of wild columbids and offer a valuable baseline for future ecological, physiological and conservation-oriented studies.
     
    Data availability statement
     
    All data generated or analyzed during this study are included in the published article. Additional supporting materials are available from the corresponding author upon reasonable request.

    CONFLICT OF INTEREST

    The author warrants that there is no conflict of interest in the manuscript.

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