Postembryonic development of the chicken bursa of Fabricius: a light microscopic histoquantitative study

Development of the bursa of Fabricius in the chicken was studied from day 4 to day 84 after hatching using light microscopic, morphometric methods. The proportion of lymphoid follicles of the total bursal tissue increased from 62% at day 4 to 86% at day 63 and thereafter decreased slightly until day 84. The corresponding values for bursal stroma and epithelium decreased from day 4 to day 84. The relative and absolute amounts of lymphoid tissue increased from enlargement of individual lymphoid follicles; their mean spatial diameter increased from 185 microns at day 4 to 720 microns at day 84. The number of areas of follicle-associated epithelium at the bursal mucosa, which in a mature bursa corresponds to the follicle number, remained relatively unchanged (range 7200 to 12000 per bursa). the follicular cortex grew more rapidly than did the follicular medulla, indicating different functions for each. The total surface area of the follicle-associated epithelium was .88 cm2 at day 4 increasing to 4.71 cm2 at day 63. This increase also in mainly due to increased size of the individual areas of follicle-associated epithelium (diameter increased from 71 to 168 microns). Histoquantitative findings are discussed in light of present knowledge about the function of the bursa as a central and peripheral lymphoid organ.