Age-related morphological changes in the thymus of indigenous Large White pig cross during foetal and postnatal development

Abstract

Objectives: The thymus is found in all vertebrates, the structure of the thymus differs markedly among species. This study investigated the gross anatomy, morphometric and histological changes of the thymus in the indigenous Large White pig cross at various ages of foetal and postnatal periods. Methods: The study used slaughter house specimens obtained after adequate health inspection and slaughter. A total of fifty three samples of thymus collected from foetal, prepubertal and pubertal pigs with varied weights were used for gross and histological study. Results: The absolute thymus weight showed significant (p<0.05) increase in size with advancing foetal age, but the increment was not significant in the postnatal stage. The capsule was initially thin and indistinct at 30–45 days thymus, but increased in thickness with progression of gestation. A distinct evidence of lobulation was observed in foetuses of 46–58 days of gestation. Interlobular septa matured and increased in vascularization with age, such that they were highly vascularized at 77–90 days thymus. The boundary of cortex-medulla was partially distinguishable at 46–58 days foetuses and distinctively demarcated at 60–75 days of gestation. Various sizes of lymphocytes were apparent in the cortex at 60–75 days impacting a strong basophilic colour to the cortex. Rudiments of epithelial cells were seen as eosinophilic clumps at 30–45 day thymus. Apparently well differentiated epithelial cells with dense consistency were observed at 46–58 days thymus. Macrophages were seen at the 95–113 days and were quite distinct at the prepubertal and pubertal age. Early forms of Hassal’s corpuscles were present at 46–58 day thymus and increased in number with age. Conclusion: The present study has demonstrated that the morphology of the thymus changed with age and the cellular components of the thymus attain morphological maturity during the late foetal period and may be involved in moderate prenatal immunological functions.