Shahid Bahonar University of Kerman and Iranian Biotechnology Society Agricultural Biotechnology Journal 2228-6705 18 3 2026 08 23 Sequential morphohistological and scanning electron microscopic developmental study of thymus at prenatal stages in Iraqi Awassi sheep fetuses Sequential morphohistological and scanning electron microscopic developmental study of thymus at prenatal stages in Iraqi Awassi sheep fetuses 313 332 5425 10.22103/jab.2026.27058.1877 FA Zahraa Mazin Mahdi Department of Veterinary Anatomy, Veterinary College, Qasim Green University, Babylon 51013, Iraq. 0000-0002-1863-148X Jafar Ghazi Abbas Al-Jebori Department of Veterinary Anatomy, Veterinary College, Qasim Green University, Babylon 51013, Iraq. 0009-0007-8070-8234 Journal Article 2026 04 25 ObjectiveOne of the primary lymphoid organs is the thymus, which is of great importance during prenatal and early life. It is responsible for the growth, maturation, and selection of thymocytes and plays a role in the development of T-cell functional competence and central immune tolerance, which is closely related to its specialized histological architecture. This study investigates the prenatal morphological and histological development of the thymus gland in local Awassi sheep with scanning electron microscopy (SEM). Materials and methodsThirty thymus specimens were collected from healthy pregnant ewes at different stages of gestation. Fetal age was determined using the fetal crown rump length (CRL) equation and the specimens were classified into three groups: Group 1: 50–55 days, Group 2: 90–100 days, and Group 3: 130–140 days. scanning electron microscopy (SEM) was used to observe the thymic surface at multiple magnifications. Data analysis of histological and morphological parameters was performed using the Statistical Package for the social sciences (SPSS).ResultsIn Group 1, thymus was small, underdeveloped organ with soft lobes and thin capsule without connection between cervical and thoracic part. Scanning electron microscopy and histologically revealed an immature surface structure, irregular thymic cells, an unclear connection between the cortex and the medulla, reflecting early thymic differentiation. While in Group 2, the thymus showed an increase in size and improved lobular organization to revealed a more clearly defined cortical-membrane boundary, the growth of tissue bundles extending from the capsule to the viscera, and a higher density of cortical thymus cells. The medullary region also showed reticular epithelial cells, indicating progressive structural maturation. In group 3, thymus was well-developed with prominent lobes separated by connective tissue septa. Histological and Scanning observations revealed highly organized visceral tissue, a clear cortical-membrane boundary, extensive reticular epithelial cells, and fully formed Hassall’s corpuscles within the medulla, demonstrating advanced prenatal microstructural maturation. ConclusionThese findings highlight the progressive prenatal maturation of the thymus and underscore its pivotal role in immune system development. Deviations from these normal microstructural patterns may indicate pathological or immunological disorders. ObjectiveOne of the primary lymphoid organs is the thymus, which is of great importance during prenatal and early life. It is responsible for the growth, maturation, and selection of thymocytes and plays a role in the development of T-cell functional competence and central immune tolerance, which is closely related to its specialized histological architecture. This study investigates the prenatal morphological and histological development of the thymus gland in local Awassi sheep with scanning electron microscopy (SEM). Materials and methodsThirty thymus specimens were collected from healthy pregnant ewes at different stages of gestation. Fetal age was determined using the fetal crown rump length (CRL) equation and the specimens were classified into three groups: Group 1: 50–55 days, Group 2: 90–100 days, and Group 3: 130–140 days. scanning electron microscopy (SEM) was used to observe the thymic surface at multiple magnifications. Data analysis of histological and morphological parameters was performed using the Statistical Package for the social sciences (SPSS).ResultsIn Group 1, thymus was small, underdeveloped organ with soft lobes and thin capsule without connection between cervical and thoracic part. Scanning electron microscopy and histologically revealed an immature surface structure, irregular thymic cells, an unclear connection between the cortex and the medulla, reflecting early thymic differentiation. While in Group 2, the thymus showed an increase in size and improved lobular organization to revealed a more clearly defined cortical-membrane boundary, the growth of tissue bundles extending from the capsule to the viscera, and a higher density of cortical thymus cells. The medullary region also showed reticular epithelial cells, indicating progressive structural maturation. In group 3, thymus was well-developed with prominent lobes separated by connective tissue septa. Histological and Scanning observations revealed highly organized visceral tissue, a clear cortical-membrane boundary, extensive reticular epithelial cells, and fully formed Hassall’s corpuscles within the medulla, demonstrating advanced prenatal microstructural maturation. ConclusionThese findings highlight the progressive prenatal maturation of the thymus and underscore its pivotal role in immune system development. Deviations from these normal microstructural patterns may indicate pathological or immunological disorders. https://jab.uk.ac.ir/article_5425_8e621619d71d0ae5ef4e631ad586334f.pdf