Advances in Research

The spleen is the largest secondary lymphoid organ in birds and plays a fundamental role in immune functioning. Comparative information on the post-hatch development of the spleen is crucial for understanding differences in immunocompetence between indigenous and commercial chickens. Therefore, the present study compared the gross morphology, histomorphometry, and histochemistry of the spleen in indigenous Haringhata Black chickens and commercial broiler chickens during the post-hatch period across five age groups (days 0, 15, 30, 45, and 60). Grossly, the spleen was roughly triangular and dark reddish in colour, with rounded edges, and was located at the junction of the proventriculus and gizzard in both breeds. The biometric values (length, breadth, and weight) increased progressively with age, with peak values around 30–45 days. A greater transverse diameter of the spleen was recorded in commercial broilers than in Haringhata Black chickens at corresponding ages. Histologically, the parenchyma comprised white pulp organised around a periarterial lymphatic sheath (PALS) and red pulp with splenic cords and venous sinuses, separated by a marginal zone. The collagen fibre content in the capsule and PALS increased with age, and this increase was more prominent in broilers and Haringhata Black chickens. Various micrometric parameters, namely the length and width of the white pulp, diameter of splenic nodules, thickness of the capsule and PALS, and diameter of the central artery, increased with age in both breeds. A thicker PALS was observed in Haringhata Black chickens than in broilers. The presence of neutral and acidic mucopolysaccharides was noted in the capsule, connective tissue, white pulp, and red pulp. Peak Periodic Acid–Schiff (PAS) and Alcian blue activity was observed between days 15 and 45 in both breeds, followed by a decline. These findings establish a comparative baseline anatomical and developmental profile of the spleen in indigenous and commercial broiler birds. This study also reports a proportionately better-organised blood–spleen barrier with slower growth in Haringhata Black chickens, which is pertinent to poultry immunobiology and indigenous breed conservation.