Journal of Animal Science and Veterinary Medicine

The avian spleen is a primary peripheral lymphoid organ located in the region dorsal to the gonad, ventral to the liver and lateral to the stomach, just opposite the dorsal surface of the right hepatic lobe. It plays both lymphopoietic and hematopoietic roles, depending on the respective amounts of white pulp and red pulp elements in the parenchyma. The pre- and post-hatch development of the spleen of native chicken ecotype predominant in the south eastern region of Nigeria was studied from embryonic incubation day (EID) 10 to day (D) 42 post hatch using gross anatomical and histological techniques to detect age-related developmental changes associated with the spleen and the relative time of establishment of the basic immunological structures of the spleen. The embryos were harvested from the eggs at different embryonic ages for the pre-hatch studies. The spleen was collected through a ventral abdominal incision in both embryos and post-hatch chicks, weighed and fixed in neutral-buffered formalin. The fixed tissues were routinely processed and stained with haematoxylin and eosin (H&E) for histological studies. The mean weight of the spleen increased significantly (p < 0.05) between D 14, 28 and 42, while the relative weight varied significantly between D 14 and 28. The spleen was bean-shaped at EID 10 and throughout the post-hatch periods, but it became triangular at EID 14. The colour was relatively red in both embryos and post-hatch chicks. At EID 10, the parenchyma was undifferentiated into white and red pulp regions, but splenic sinusoids had developed. At EID 14, lymphocytes had infiltrated into the parenchyma and white and red pulp zones fairly distinct. Apparent white and red pulp regions appeared at EID 18, but were more prominent at hatch (D 0). Ellipsoids and periarteriolar lymphoid sheath equally developed at hatch. By D 7, the arterial wall and the capsule increased in thickness. The parenchyma appeared to be dominated by the white pulp elements between D 0 and D 42. There was also a progressive increase in lymphocyte densities during the post-hatch periods, but splenic nodules only developed at D 42. The development of the spleen as a functional peripheral lymphoid organ in native chickens of Nigeria occurred in the embryos but progresses after hatch, and the dominance of the parenchyma by the white pulp during the embryonic and early post-hatch periods of development emphasised lymphopoietic responsibility of the spleen in Nigerian native chicken.