Abstract
Indigenous Naked-neck chickens in hot agroecological zones may develop digestive tract adaptations that improve mechanical and enzymatic digestion. However, in Ethiopia, there is no documentation of the gross morphological and histological features of the proventriculus and ventriculus in Naked-neck chickens. This study aimed to investigate these features. To carry out this study, an exploratory research design using a purposive sampling was employed to select eight clinically healthy chickens in the Quara district from January to November 2024. For histological studies, tissue samples were collected, fixed in 10% neutral buffered formalin, processed using the paraffin technique, and stained with hematoxylin and eosin. The stained tissues were examined under a light microscope, and histometric analysis was performed using ImageJ software. The proventriculus was characterized by a markedly developed tunica submucosa (2077.32 ± 27.56 µm), whereas the ventriculus had a thicker tunica muscularis (2104.82 ± 63.36 µm), suggesting enhanced mechanical grinding capacity. Proventricular gland lobules showed polymorphic architecture, including rounded conical, hexagonal, and irregular forms. This pronounced muscular development of the ventriculus may be consistent with mechanical digestive requirements, but further comparative and functional studies are needed.
Keywords: Gross morphology, Histology, Naked-neck chicken, Proventriculus, Ventriculus
Introduction
Poultry comprises domesticated avian species, such as chickens, turkeys, ducks, pigeons, and geese, which are kept worldwide for meat and egg production. Africa hosts a significant portion of the global chicken population, with South Africa being the largest commercial chicken-producing country on the continent, followed by Egypt, Morocco, Nigeria, and Algeria (Nkukwana, 2018).
Ethiopia has diverse agroecological zones (Fentie et al., 2026) and favourable environmental conditions that foster a flourishing poultry sector. Poultry production in Ethiopia plays a significant role in the producing of eggs for hatching, marketing, and household consumption, as well as in the producing of chickens for sale, processing, and domestic use (Ebsa et al., 2019). The indigenous chicken excels across diverse agroecological zones under traditional (Muluneh et al., 2023), family based management, which has unique genetic combinations and specialized traits, that are absent in modern improved breeds (Kindie and Tamiru, 2021).
The Naked-neck chicken ecotype has been documented in several regions of Ethiopia, such as in the Sheka zone (Assefa and Melesse, 2018), the southern region in Ethiopia (Melesse and Negesse, 2011), in Jawi (Muluneh et al., 2023), and in Quara (Getu et al., 2014). Locally, indigenous Naked-neck chickens are known as “Angete Melata” (Melesse et al., 2010). According to a report by Getu et al. (2014), these chickens inhabit the hot agroecological zones of the Quara district in the West Gondar Zone. They are typically reared under a scavenging system with minimal feed supplementation and shelter. However, they are considered a promising breed for producing larger, nutrient- and mineral-rich eggs, as well as tasty meat that consumers appreciate.
Anatomically, the chicken stomach is composed of two distinct chambers (Matias et al., 2021): the cranial glandular stomach (proventriculus), which is continuous with the esophagus, and the caudal muscular stomach (ventriculus or gizzard), which connects to the duodenum (Taher et al., 2020). The proventriculus and ventriculus play a vital role in providing both the enzymatic and mechanical digestion of a chicken’s feed (Sinha et al., 2023). These organs develop rapidly in early life, reach their adult form, and then remain relatively unchanged throughout old age (Qureshi et al., 2017).
Comprehensive gross morphological and histological investigations of the chicken stomach provide solid information for understanding digestive anatomy, physiology, dietary adaptations, and health (Khaleel and Abd Alkhazraji, 2022). Gross anatomical studies elucidate of organ morphology and topographical relationships, while histological examination reveals detailed structural organization, including the epithelial lining, lamina propria, tunica submucosa, tunica muscularis, and tunica serosa, as well as associated glandular components and cellular architecture (Al-Saffar and Al-Samawy, 2016).
Literature on the gross-morphological and histological study of the avian proventriculus and ventriculus has broad implications (Yovchev, 2022). Given its importance, extensive international research has been conducted in countries, such as India (Das et al., 2017), Iraq (Al-Kafagy et al., 2022), and Egypt (AbdElnaeem et al., 2019).
However, in Ethiopia, there is no documented evidence concerning the gross morphological and histological features of the proventriculus and ventriculus in Naked-neck chickens reared under the hot agroecological conditions of the Quara district. No quantitative data exists for the thickness of the tunica mucosa, tunica submucosa, tunica muscularis, and tunica serosa. Anatomical variations in the proventriculus and ventriculus may influence digestive efficiency, feed utilization, adaptation to scavenging systems, and disease susceptibility. Understanding their normal gross and microscopic architecture is essential. This knowledge gap restricts comparative morphometric and histological analyses, the development of breed-specific nutritional strategies, and evidence-based clinical interventions for this indigenous ecotype.
The present study provides the preliminary descriptive gross and microscopic anatomical study of the proventriculus and ventriculus in Naked-neck chickens in the Quara district, Northwest Ethiopia, establishing reference data for the normal architecture of these organs.
Materials and methods
Description of study area
The study was conducted in the Quara district, West Gondar Zone, Amhara Regional State, Ethiopia (Fig. 1). It is bordered from on the South by Benishangul-Gumuz Region, on the West by Sudan, on the North by Metemma, on the East by the Takusa and Alefa Districts, and on the Southeast by Agew Awi Zone. It is located between 11°47′ and 12°21′ N latitude and 35°16′ and 35°47′ E longitude. It is 1123 km from Addis Ababa, 324 km from Gondar town. The annual temperature ranges from 25 to 44°C, with a mean annual rainfall between 600 and 1000 mm, at altitudes ranging from 530 to 1900 meters above sea level Ayeneshet et al., 2017). In the Quara district, there are 179,174 chickens, including the Naked-neck chickens, which are found in this highly arid agroecological Zone (Getu et al., 2014).
Fig. 1.
Map of the study area (Generated from QGIS, V3.34).
Study animals
The study was conducted on eight apparently clinically healthy Naked-neck chickens purchased from local farmers in the Quara District. An equal number of males and females (n = 4 each) were included. The Naked-neck chicken ecotype was identified based on distinctive phenotypic characteristics rather than genetic confirmation. Specifically, the characteristic naked neck and unfeathered vent regions served as definitive macro-morphological markers for identification. These traits are recognised as phenotypic expressions of the Naked-neck genotype and are controlled by a single autosomal dominant gene.
The chickens were categorised into two age groups: 8 months (n = 4) and 14 months (n = 4) to assess age-related gross and histomorphological variations.
Age determination was based on owner records and local management information. The health status of the chickens was evaluated through physical examinations both in the field and at the University of Gondar Veterinary Teaching Hospital. Following purchase, the chickens were transported to the College of Veterinary Medicine and Animal Sciences, University of Gondar, and acclimatized for one week under standard management conditions prior to sample collection.
Study design
An exploratory study was conducted from January to November 2024 to investigate the gross and microscopic anatomical features of the proventriculus and ventriculus in Naked-neck chickens in the Quara district, Northwest Ethiopia. The age groups (8 and 14 months) were chosen to represent post-sexual maturity and full adult maturity stages, enabling the evaluation of developmental changes.
Sampling technique
Given the endangered status and low population of the local Naked-neck chicken ecotype, a purposive sampling method was used to select birds from various smallholder households across six kebeles in Quara district. Chickens were purchased directly from farmers and selected for specific phenotypic traits to accurately identify the ecotype and distinguish it from other local chicken groups. Before inclusion, information on each bird's health, age, management, and feeding history was collected through structured interviews with the owners. All sampled chickens were raised under similar traditional, extensive management systems, mainly free-range scavenging and dependence on natural feed sources. This sampling method ensured that selected birds were representative of the study criteria and reflected variation across households in the area.
Inclusion criteria: The study focused exclusively on indigenous, apparently healthy Naked-neck chickens aged 8 or 14 months, without signs of disease, with equal sex representation (4 males and 4 females), and with owner consent to the sale of the chickens.
Exclusion criteria: Conversely, the chickens were excluded if they were not Naked-neck breed, displayed any signs of illness or poor health, fell outside the designated age ranges, or their owners were unwilling to sell them.
Data collection methods
Gross-anatomy and morphometry
After the chickens had acclimated to their environment, they were thoroughly examined clinically to ensure their health status at the University of Gondar Veterinary Teaching Hospital. The body weight of the chickens was measured using a balancing scale before they were euthanised with sodium pentobarbitone (140 mg/kg, IV). Following the euthanisation of all study chickens via an intravenous injection of sodium pentobarbitone, a longitudinal incision was made along the mid-ventral line. Tissue specimens were then harvested from all chickens, targeting the proximal, middle, and distal regions of the proventriculus, as well as the thick caudodorsal and cranioventral muscles and the thin craniodorsal and caudoventral muscles of the ventriculus. The shape, color, consistency, and surface of the proventriculus and ventriculus were grossly observed and documented.
Next, the organs were carefully dissected out; and biometric measurements were taken for the length, diameter, thickness, and weight of the organs. A CTG302-300 electronic precision digital balance was used to weigh the organs (in grams), a ruler was used to measure their length, and a digital vernier calliper was used to measure the diameter and thickness of the proventriculus and ventriculus (in millimetres).
Histological sample processing
After the gross measurements were taken, cross sections approximately 5 mm in thick were cut using a surgical blade on a trimming board. These tissue specimens from both the proventriculus and ventriculus were then gently washed with tap water to remove debris. Immediately after the wash, the tissues were fixed in 10% neutral-buffered formalin. The collected specimens were transported in an ice box to the Veterinary Pathology Laboratory for further preparation and processing (Bancroft, 2018).
After 72 hours of fixation, the tissues were washed for three hours under running tap water inside tissue cassettes. To dehydrate the tissues, an ascending ethanol series (70%, 80%, 90%, and two changes of 100%) was used for 1 hour per step. Clearing was then performed using three changes of xylene (Xylene I, II, and III) for one hour each to remove the alcohol and render the tissues translucent.
After clearing with xylene, the tissue samples were immersed in paraffin baths I and II for 2 hours each at 62°C to ensure the complete removal of clearing reagent and proper paraffin infiltration. The tissues were oriented in melted paraffin, to make paraffin blocks. Following embedding, the tissue blocks were cooled overnight to facilitate the separation of the cassettes from the molds (Bancroft, 2018).
All tissue processing procedures were done within a Leica TP 1020 automatic tissue processing machine. Then the tissues were dislodging from the automatic tissue processing machine, and paraffin was poured on the plastic tissue cassette to prepare a tissue block. Once block was prepared, sections of 5 micrometre thickness were obtained using a Leica RM2235 Rotary Microtome. The sectioned ribbon was collected and placed on water bath at 54−60 °C. The relaxed ribbons on water bath were picked up on clean microscopic slide and labeled. The labelled slides were deparaffinized (xylene) and rehydrated in descending grades of ethyl alcohol (100%, 100%, 100%, 90%, and 80%). These sections were then subjected to Harris’s hematoxylin and Eosin stain techniques for general tissue architecture. Finally, the stained slides were mounted with Canada balsam with a coverslip and allowed to dry well (Bancroft, 2018), then examined under the light microscope at Woldia University Microbiology Laboratory
Histometric analysis was performed on 5-μm-thick sections obtained from three proventriculus regions (proximal, middle, and distal) and four ventricular muscular pairs (thick caudodorsal/cranioventral and thin craniodorsal/caudoventral) for all chickens. For each anatomical site, three sections were evaluated. Within each section, four perpendicular measurements were taken for each tissue layer across a single microscopic field. All histometric measurements were performed in a blinded manner, with the observer unaware of the age group and anatomical origin of the samples during analysis to minimise observer bias. All measurements were captured using ImageJ software, which was calibrated with a stage micrometer prior to analysis. Furthermore, these measurements were captured using ImageJ software, which was calibrated with a stage micrometer prior to analysis. These measurements were essential for understanding the morphological changes and structural dynamics occurring in the chicken stomach.
Gross photographs of the organs were captured using a Samsung Galaxy A12 smartphone camera. The histological slides were documented with an S-Eye (V1.10.7) digital camera mounted on a BK5000RT light microscope at the Woldia University Microbiology Laboratory.
Data management and analysis
The gross anatomical and histological data were collected, arranged, coded, and entered into an Excel Spreadsheet (Microsoft Office Excel 2016). Descriptive statistics (Means and standard deviations) were used to summarise the gross morphological and microscopic parameters of Naked-neck chickens using Stata Software.
Ethical consideration
Ethical approval for the study was granted by the University of Gondar’s College of Veterinary Medicine and Animal Sciences, Ethics Review Committee (Approval No: CVMASc/UoG/RERC/12/03/2024) on April 1, 2024.
Results
Gross anatomical examination revealed that the stomach of the Naked-neck chickens consists of two distinct compartments: the cranial proventriculus and the caudal ventriculus. These compartments were interconnected by a middle transitional region known as the isthmus (Fig. 2C).
Fig. 2.
Gross view of the stomach and other organs in Naked-neck chickens.
A. Left lobe of liver (1), fatty tissue with ventriculus (2), and duodenum (3). (B) Esophagus (1), proventriculus (2), ventriculus (3), duodenum (4). (C) Isthmus (1), craniodorsal thin muscle (2), caudoventral thin muscle (3), caudodorsal thick muscle (4), cranioventral thick muscle (5). (D) Longitudinal mucosal fold (1), grit and stones (2), proventricular papillae (3), incised muscle in ventriculus (4) cuticles (5).
The proventriculus was a spindle-shaped, tubular organ located between the oesophagus and the ventriculus. Anatomically, it was situated dorsal to the liver (Fig. 2A). The external surface of the proventriculus was smooth and light red, providing a clear macroscopic demarcation from the preceding oesophagus, which exhibited a whitish outer surface. Internally, the oesophageal mucosa was smooth, whereas the proventriculus was whitish and featured macroscopic papillae distributed across its entire surface (Fig. 2B, C, D). The proventricular lumen narrowed at the cranial and caudal extremities and widened centrally.
Furthermore, the ventriculus was a highly muscular, disc-shaped organ enveloped by yellowish adipose tissue. It was located to the left of the midline plane, located between the proventriculus and the duodenum, and was partially covered by the left hepatic lobe. The cranial border of the ventriculus connected to the isthmus, while its caudal border joined the duodenum on the left side (Fig. 2D). The external surface was covered by a glossy layer of tendinous tissue that was thicker centrally and tapered toward the peripheral margins. Internally, the ventriculus was lined with a thick, firm koilin layer featuring distinct mucosal folds. Small pieces of grit and stones were observed within the ventricular lumen (Fig. 2D).
The descriptive data indicated that the overall mean total body weight of the two age groups of Naked-neck chickens was 1.78±0.28 kg. Morphometric values, including organ weight, length, diameter, and wall thickness for both the proventriculus and ventriculus, with respect to age were presented in Table 1.
Table 1.
Age-related morphometric parameters (Mean ± SD) of the proventriculus and ventriculus in Naked-neck chickens (N = 8).
|
Mean ± SD (n=8) |
||||
|---|---|---|---|---|
| Organs | Parameters | 8-month (n = 4) | 14-month (n = 4) | Average |
| Chicken body weight (Kg) | 1.63 ± 0.24 | 1.94 ± 0.24 | 1.78 ± 0.28 | |
| Proventriculus | weight with ingesta(g) | 19.94 ± 1.32 | 25.20 ± 1.32 | 22.57 ± 3.05 |
| weight without ingesta(g) | 17.45 ± 1.24 | 23.68 ± 3.48 | 20.56 ± 4.13 | |
| Length(mm) | 38.35 ± 4.57 | 42.67 ± 4.57 | 40.64 ± 5.08 | |
| Diameter (mm) | 8.69 ± 1.00 | 9.44 ± 1.08 | 9.06 ± 1.05 | |
| Thickness (mm) | 3.20 ± 0.34 | 3.66 ± 0.38 | 3.43 ± 0.41 | |
| Ventriculus | Weight with ingesta(g) | 65.76 ± 9.24 | 75.97 ± 5.20 | 70.87 ± 8.40 |
| Weight without ingesta (g) | 57.39 ± 9.60 | 63.83 ± 6.96 | 60.61 ± 8.49 | |
| Length (mm) | 56.64 ± 7.11 | 72.13 ± 6.60 | 64.00 ± 10.16 | |
| Diameter (mm) | 39.93 ± 1.58 | 41.40 ± 1.94 | 40.67 ± 1.81 | |
| Thickness (mm) | 43.93 ± 3.30 | 56.72 ± 4.56 | 50.30 ± 7.78 | |
SD stands for Standard Deviation.
The wall of the proventriculus comprised four distinct layers, arranged from innermost to outermost: the tunica mucosa, tunica submucosa, tunica muscularis, and tunica serosa. Of these, the tunica mucosa was relatively thin, with an average thickness of 94.54 ± 5.52 µm. It had a simple columnar epithelium, lamina propria, and mucosal grooves, with the loose connective tissue of the lamina propria housing simple tubular glands. Among all the layers, the tunica submucosa was the thickest layer, situated between the lamina propria and the tunica muscularis with an average thickness of 2077.32±77.95 µm (Fig. 3A).
Fig. 3.
Longitudinal section of the proventriculus wall in a Naked-neck chicken. (A) Mucosa (1), tunica submucosa (2), tunica muscularis (3), and serosa (4) (H&E stain, 100x). (B) Blood vessel in the tunica serosa(1) (H&E stain, 100x). (C) Proventricular glands (1), tunica muscularis with abundant collagen fibers (2) (H&E stain, 100x). (D) multilobulated tubular gland (1), interlobular connective tissue septa in the proventricular gland (2) and main duct in the tunica submucosa (3) (H&E stain, 100x).
Two morphologically distinct categories of proventricular glands were identified within the submucosa: tubuloalveolar and multilobulated tubular glands (Fig. 3C, B; Fig. 4A, B). The multilobulated tubular glands were numerous numerous and spread throughout the entire organ (Fig. 3C, D). These glands were compound, composed of rounded, conical, oval, hexagonal, or polymorphic lobules in shape, separated by inter-lobular connective tissue septa and a few smooth muscle fibers (Fig. 5C). Each lobule was formed by numerous secretory tubules, which opened into duct. The tubules of the proventricular glands were composed of oxyntic-peptic cells (Fig. 5C). Several secondary ducts merged to form a primary duct, which opened into a prominent mucosal papilla (Fig. 5B). Ducts from several lobules joined together to form a short main duct (Fig. 3D), which connected to the apex of the raised mucosal papillae and opened into the narrow lumen of the proventriculus.
Fig. 4.
Microscopic illustration of the proventricular gland type in the Naked-neck chicken. (A) Oval-shaped lobule, tubular proventricular gland in the tunica submucosa (1), main duct (2) (Stained: H and E, 100x). (B) Tubuloalveolar proventricular gland in the tunica submucosa (1) (Stained: H and E, 100x).
Fig. 5.
Longitudinal section of the proventriculus wall of the Naked-neck chicken. (A) interlobular connective tissue (1) and Proventricular lobule (2) (H and E stained, 100X). (B) Main duct (1), primary duct (2), and secretory tubules (3), and a columnar oxynticopeptic cell (4) (H and E stained, 100x). (C) Various shapes of lobules in the proventricular glands (1) (H and E stained, 100x).
The tunica muscularis was a smooth muscles layer, occupying a small space in the wall of the proventriculus (Fig. 3C). The inner layer was arranged in a circle, while the outer layer was arranged in a line. The total thickness of the tunica muscularis layer was 182.01±11.99 μm. The last tunicae were serosae, which consisted of loose connective tissue containing blood vessels, lymphatic vessels, and adipose tissue (Fig. 3B). The average thickness of this layer was 171.49±12.73 μm (Table 2).
Table 2.
Histometric parameters (Mean ± SD) of Proventriculus wall thickness in Naked-neck chickens with respect to age (µm) (N = 8).
| Mean ± SD | |||
|---|---|---|---|
|
Age |
|||
| Parameters | 8-months(n = 4) | 14-months(n = 4) | Average |
| Mucosa | 89.48 ± 16.88 | 98.24 ± 9.78 | 94.54 ± 5.52 |
| Submucosa | 2017.05 ± 227.88 | 2137.59 ± 259.92 | 2077.32 ± 77.95 |
| Muscularis | 174.70 ± 11.84 | 200.96 ± 7.76 | 182.01 ± 11.99 |
| Serosa | 158.25 ± 21.20 | 173.27 ± 13.96 | 171.49 ± 12.73 |
SD stands for Standard Deviation.
Similar to the proventriculus, the ventricular wall consisted of the tunica mucosa, tunica submucosa, tunica muscularis, and tunica serosa. However, these walls were thicker than those of the proventriculus (Fig. 6). The descriptive histometric values for the thickness of each ventricular tunic were summarised in Table 3.
Fig. 6.
Transverse section of the ventriculus wall in a Naked-neck chicken. (A) Tunica mucosa (1), tunica submucosa (2), and tunic muscularis mucosae (3) (H and E stained, 100X). (B) Mucosal groove (1), outer longitudinal muscle layer (2) and tunica serosa (3) (H and E stained, 100X).
Table 3.
Histometric parameters (Mean ± SD) of the ventriculus wall thickness in Naked-neck chickens with respect to age (µm) (N = 8).
| Mean ± SD | |||
|---|---|---|---|
| Age | |||
| Parameters | 8-months (n = 4) | 14-months (n = 4) | Average |
| Mucosa | 1048.56 ± 220.34 | 1222.82 ± 174.06 | 1135.71 ± 104.86 |
| Submucosa | 935.27 ± 149.28 | 1006.90 ± 136.28 | 976.11 ± 42.82 |
| Muscularis | 1949.29 ± 115.24 | 2258.30 ± 207.00 | 2104.82 ± 179.21 |
| Serosa | 57.30 ± 7.18 | 66.83 ± 12.62 | 62.06 ± 5.52 |
SD stands for Standard Deviation.
The tunica mucosa was the innermost layer consisting of invaginating mucosal folds and grooves (Fig. 6B). This tunic was composed of a simple columnar epithelium, a lamina propria, and lamina muscularis mucosae. The epithelium was simple columnar (Fig. 8A), which possessed thin, finger-like projected toward the lumen (Fig. 7A, B), and continuous within the compound tubular mucosal glands (Fig. 8B) that were found in the lamina propria (Fig. 8A). The lamina propria was composed of connective tissue, compound tubular glands, blood vessels, and lymphatic infiltration. The mucosa of the ventriculus was coated with a thick cuticle layer, produced by compound tubular glands (Fig. 7B; Fig. 8A). This study confirmed that lamina muscularis mucosae were present in the wall of the ventriculus (Fig. 7B).
Fig. 8.
Transverse section of the ventriculus wall in a Naked-neck chicken. (A) koilin (1), simple columnar epithelium (2), lamina propria (3), submucosa (4) and inner circular muscle layer (5) (Stained: H and E, 400X). (B) Compound tubular glands (1) (Stained: H and E, 400X).
Fig. 7.
Transverse section of the ventriculus wall in a Naked-neck chicken.
(A) Lumen (1), mucosal gland in tunica mucosa (2), submucosa (3) and tunica muscularis (4) (Stained: H and E, 100x). (B) Cuticle (blue star), lamina muscularis mucosae (1), submucosa (white star) and inner circular muscularis layer (2) (Stained: H and E, 100x).
The ventricular submucosa of the Naked-neck chicken was thin and consisted of loose connective tissue. The tunica muscularis was the thickest layer, composed of well-developed smooth muscle bundles organised into an inner circular layer and an outer longitudinal layer. The mean thickness of this layer was 2104.82 ± 104.86 µm. The tunica serosa was the outermost layer, composed of loose connective tissue, including adipose, nerves, and blood vessels.
Discussion
This study provides the first comprehensive gross anatomical and histological baseline of the proventriculus and ventriculus in the local Naked-neck chicken ecotype (Gallus gallus domesticus) from Northwest Ethiopia. Although the division of the avian stomach into proventricular and ventricular compartments is a consistent morphological feature across avian species, the observed morphometric and histological differences suggest functional specialization associated with breed-specific digestive demands. These results were aligned with those in the wild bronze turkey (Yovchev, 2022) and in the swan goose (Alumeri, 2023).
The clear macroscopic demarcation between the oesophagus and proventriculus in the Naked-neck chicken’s stomach was indicated by pronounced papillae corresponding to underlying proventricular glands, indicates a well-developed secretory apparatus in the Naked-neck chickens. This anatomical specialisation suggests an enhanced capacity for the secretion of hydrochloric acid and pepsinogen, which is essential for initiating protein digestion. Similar structures reported in Japanese chicken and wild bronze turkey likely reflect conserved digestive architecture (Sinha et al., 2023); however, differences observed in species such as crows (Khalaf et al., 2023) and laughing doves(Al-Kinany, 2019), may be attributed primarily to dietary ecology, as omnivorous and opportunistic feeders often exhibit greater variability in digestive specialisation. In contrast, Naked-neck chickens raised under scavenging systems in Ethiopia are frequently exposed to fibrous, heterogeneous feed resources, which may help maintain pronounced secretory structures that support efficient chemical digestion.
The ventriculus was highly muscular and lined by a distinct koilin layer, a feature also reported in granivorous birds such as pigeons (Kausar et al., 2019. In contrast, reduced or absent koilin layers in carnivorous species such as owls are likely related to reduced mechanical processing requirements due to soft-prey diets (Al-Saffar and Eyhab, 2014; Khalaf et al., 2023). Therefore, variation in koilin development across avian species is best interpreted as an adaptive response to dietary texture rather than a strict taxonomic difference. In Naked-neck chickens, the well-developed koilin layer is consistent with the need for mechanical grinding of coarse feed particles commonly encountered in scavenging-based production systems. Although the four-layered organization of the avian stomach (mucosa, submucosa, muscularis, and serosa) is structurally conserved, differences in relative layer thickness across studies likely arise from both biological and methodological factors. Biological explanations include species and breed differences, age, feeding ecology, and environmental adaptation (Jassem et al., 2016; Kadhim et al., 2011; Sultan et al., 2023). Methodological variation may also contribute substantially, including differences in sampling location within the organ, fixation-induced tissue shrinkage, section orientation, and histometric measurement protocols, all of which are known to influence quantitative histological outcomes (Bancroft and Gamble, 2008).
The relatively well-developed muscularis and submucosal glandular regions observed in Naked-neck chickens suggest enhanced mechanical and secretory capacity. Compared with Red Jungle Fowl and other avian species, these differences may reflect post-domestication morphological remodeling associated with adaptation to scavenging-based feeding systems and environmental stressors (Kadhim et al., 2011; Khalaf et al., 2023). However, in the absence of controlled dietary, age-matched, and ecological data, functional interpretations should be approached with caution.
Similar to the proventriculus, the ventricular wall was composed of the tunica mucosa, submucosa, muscularis, and serosa. This observation regarding the ventriculus walls were aligned with those in the swan goose (Alumeri, 2023). On the other hand, this finding did not align with wild bronze turkey (Yovchev, 2022). These differences could be due to variations in the feeding habits, breed, and ecological adaptations among the species.
Th compound tubular mucosal glands were found in lamina propria of Naked-neck chicken’s ventriculus walls, this structure was documented in wild bronze turkey (Yovchev, 2022) This study confirmed that the presence of the lamina muscularis mucosae in the walls of the ventriculus. These histological observations were inconsistent with previous studies conducted on the Red Jungle Fowl (Kadhim et al., 2011). When compared with the Red Jungle Fowl distinct differences in lamina muscularis mucosae definition and glandular arrangement suggest post-domestication remodelling of gastric architecture The Red Jungle Fowl, adapted to forest-based foraging systems with diverse, relatively softer dietary items, may exhibit a broader digestive flexibility. In contrast, Naked-neck chickens reared under arid Ethiopian conditions are frequently exposed to coarse, fibrous, and harder feed materials within scavenging production systems. Consequently, enhanced muscular development and reinforced mucosal structures may represent adaptive modifications that optimise both chemical and mechanical digestion under environmentally constrained nutritional conditions.
The overall mean ±SD values for ventricular wall thickness in the tunica mucosa, tunica submucosa, tunica muscularis, and tunica serosa of Naked-neck chickens were 1135.71 ± 104.86 µm, 976.11 ± 42.82 µm, 2104.82 ± 179.21 µm, and 62.06 ± 5.52 µm, respectively. The histometric data for the ventriculus in Naked-neck chicken differed from those swan geese (Alumeri, 2023). The tunica mucosa in Naked-neck chickens was 1135.71±104.86 µm, which was considerably thicker than the mucosa in swan geese, which was recorded at only 521.28±1.592 µm. These thickness differences suggested a more important digestive capability.
The ventricular submucosa of the Naked-neck chickens was thin and consisted of loose connective tissue, consistent with findings in the pigeon (Bansal et al., 2023), and in the crow (Khalaf et al., 2023). The tunica muscularis formed the thickest component of the ventricular wall, composed of prominent smooth muscle bundles organised into an inner circular layer and an outer longitudinal layer. In Naked-neck chickens, a well-developed tunica muscularis serves to compensate for the absence of true masticatory organs. These histological features were consistent with those reported in the wild bronze turkey (Yovchev, 2022). These histological observations were inconsistent with previous studies conducted in red jungle fowl (Kadhim et al., 2011). The distinct histometric values recorded for the ventricular layers in the Naked-neck chickens, and their subsequent variations from previous reports, can be attributed to a complex interplay of ecotype, breed, agroecological conditions, feed types, and methodological differences.
The tunica serosa was the outermost layer in the Naked-neck chickens, composed of loose connective tissue containing adipose tissue and blood vessels. This finding coincided with observations in the domestic duck (Hassan and Moussa, 2012).
Overall, while the fundamental architecture of the avian stomach is conserved, the variation observed in this study is likely the result of the combined influences of species- or breed-specific genetics, dietary ecology, environmental conditions, and methodological differences in histological processing and measurement. The gross anatomical and histological characteristics observed in the proventriculus and ventriculus of Naked-neck chickens provides valuable baseline information on the digestive morphology of this indigenous ecotype. However, the functional significance of these features should be interpreted with caution. Although certain anatomical characteristics may potentially influence digestive performance, the present study did not evaluate diet composition, feeding behaviour, environmental conditions, or comparative control breeds. Therefore, any inference regarding adaptation to fibrous scavenging diets or environmental stressors remains speculative. Future studies incorporating dietary characterisation, feeding ecology, environmental assessments, physiological measurements, and comparisons with other chicken ecotypes are required to determine whether the observed morphological features are associated with specific functional or adaptive advantages.
Limitation: Although this study provides, for the first time, a description of the gross anatomical and histological features of the proventriculus and ventriculus in Naked-neck chickens, several limitations should be acknowledged. The relatively small sample size and purposive sampling approach, largely influenced by the availability of study animals and resource constraints, may limit the generalisability of the findings. In addition, the absence of a defined control breed and of dietary information limits the ability to evaluate potential genetic and nutritional influences on the observed morphological characteristics. The limited scope of histometric analysis may also reduce the representativeness of quantitative measurements across different regions of the organs. Furthermore, the absence of histochemical staining (e.g., Masson’s trichrome, PAS, and Alcian blue) constrained detailed interpretation of collagen distribution and mucous gland characterisation. Collectively, these limitations should be considered when interpreting the results, and future studies incorporating larger, more diverse sample populations, controlled, comparative groups, and complementary histochemical techniques are recommended to strengthen and extend these findings.
Conclusion
This preliminary study provides baseline descriptive information on the gross anatomy, histology, and morphometric characteristics of the proventriculus and ventriculus, as well as digestive tract measurements, in Naked-neck chickens from Northwest Ethiopia. Although some age- and sex-related variations were observed, the limited sample size precludes broad biological, functional, or adaptive interpretations. Therefore, these findings should be regarded as preliminary observations. Future studies incorporating larger sample sizes, standardised sampling procedures, histochemical techniques, dietary assessments, and comparative analyses with other chicken ecotypes are needed to validate the present findings and better elucidate their functional and adaptive significance.
Declaration of ethical approval
In this study, all experimental procedures were approved by the University of Gondar’s College of Veterinary Medicine and Animal Sciences, Animal Research Ethics and Review Committee (Approval No: CVMASc/UoG/RERC/12/03/2024) on April 1, 2024.
Declaration of generative AI and AI-assisted technologies in the writing process
During the preparation of this manuscript, the authors used the Large language model (LLM) to enhance readability and language clarity. After using this tool/service, the authors reviewed and edited the content as needed and took full responsibility for the content of the published article.
Funding
There is no specific funding for this work.
Author Contributions
Teketay Bayleyegn Derso: conceived and designed the study, performed the main experiments, acquired funding, collected and curated data, performed statistical analysis, developed methodology, conducted investigations, validated results, prepared the original draft, revised the manuscript, and created visualizations. Mebrie Zemene Kinde: assisted in study design, contributed to methodology development, conducted laboratory investigations, validated findings, prepared sections of the original draft, revised the manuscript, and contributed to visualizations. Assaye Wollelie Fentie: participated in study design, contributed to methodology development, assisted in laboratory investigations, validated results, prepared parts of the original draft, revised the manuscript, and contributed to visualizations. Merawi Kindu Birhanie: contributed to methodology development, assisted in laboratory investigations, validated findings, prepared sections of the original draft, revised the manuscript, and contributed to visualizations. Ashenafi Wondye Dagne: assisted in methodology development, contributed to laboratory investigations, validated results, prepared parts of the original draft, revised the manuscript, and contributed to visualizations. Zerihun Getie Wassie: participated in methodology development, assisted in laboratory work, conducted data collection, validated findings, prepared sections of the original draft, revised the manuscript, and contributed to visualizations. Abebe Tesfaye Gessese: assisted in data collection, methodology development, provided technical support, supervised the research process and contributed to manuscript review. Animaw Andargie Worku: assisted in laboratory procedures, provided technical support, assisted data collection, prepared sections of the original draft, and contributed to manuscript review. Yihenew Getahun Ambaw: supported field sampling, provided technical assistance, and contributed to manuscript editing. Assaye Desta Amare: assisted in data collection, provided technical support, and contributed to manuscript review. Saleamlak Abebe Bihonegn: provided technical assistance during laboratory work and contributed to manuscript editing. Bemrew Admassu Mengistu: provided overall work supervision, assisted in fieldwork, validated results, provided technical support, performed statistical analysis, developed methodology, supervised the research process, coordinated project administration, and contributed to manuscript revision. All authors read and approved the final version of the manuscript.
Disclosures
The authors declare no conflicts of interest.
Acknowledgments
The authors would like to thank all the farmers in Quara district who participated in the study.
Footnotes
Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.psj.2026.107360.
Appendix. Supplementary materials
Data availability
The data used for analysis are available from the corresponding author upon reasonable request.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
Data Availability Statement
The data used for analysis are available from the corresponding author upon reasonable request.