Background: Kosali cattle are a native breed from Chhattisgarh, India, primarily raised in rural areas on agricultural residues. However, there is limited information about the prenatal development of their thymus. Therefore, current study was conducted to understand the prenatal morphohistogenesis of thymus in Kosali breed of cattle. 
 
Methods: The present investigation involves 24 Kosali foetuses for the prenatal gross morphometric development of the thymus and categorized on the basis of crown-rump length (CRL) into four groups: Group I (CRL &lt;20 cm), Group II (20-40 cm), Group III&nbsp; (40-60 cm) and Group IV (&gt;60 cm). A midventral cervical incision from the larynx to the thoracic inlet was made to expose the thymus for in situ examination of its topography and morphology. Thymus samples were collected and processed for Hematoxylin and Eosin, Van Gieson&rsquo;s, Verhoeff&rsquo;s and Gomori&rsquo;s staining for histological changes. 
 
Result: In Group I, the thymus had paired cervical parts and one unpaired thoracic part, with the right limb extending to the middle thyroid cartilage and the left to the cricoid cartilage. By Groups II to IV, the left limb shifted laterally. The thymus color changed from cream to pink and while lobes became more distinct, their number decreased and size increased. The capsule thickened and became more vascular. The stroma contained interlobar and interlobular septa that thinned over groups and the number of lobules per field decreased significantly, indicating involution of the thymus and functional adaptations with age. These observations suggest that the thymus undergoes progressive involution with age. The structural and vascular changes seem to reflect the functional adaptations that occur during development. 
&nbsp;

Prenatal Morphohistogenesis of Thymus in Kosali Breed of Cattle: A Developmental Study of Histological Changes during Embryonic Development