Postnatal development of the bursa of fabricius in duck (Anas platyrhynchos)

Abstract

The structure and post natal development of the bursa of Fabricious in White Pekin ducks were investigated using 51 birds aged from day – old to 155 – days. The growth, morphology and histology of the bursa were studied using three birds of each age group. In the day – old ducklings, the bursa could be seen as a smooth, yellow, elongated blind sac – like structure with a tapering apex. By 155 days it was a cylintrical and much reduced pale structure. In all the birds, the bursa communicated with the proctodeum of cloaca by a short stalk. The inner surface of bursa contained two large well – developed plicae on the ventral aspect and about five to eight smaller folds all round the circumference. The number of plicae increased upto 30 days of post natal life. After 80 days a decreasing trend was recorded in their number. After hatch, the bursal growth rate was not in proportion to that of body. It showed a decreasing trend after attaining peak values at five days of age. Though the bursa weight varied with variation in the age and body weight of the bird, a greater percentage variation in its weight was accounted for by body weight. The weight, length, diameter and plical measurements of bursa attained maximum average values at 58 days of age indicating that the bursa of ducks may be most functional at this age. Histologically, the wall of the bursa was divided into three tunics in birds of all ages. The outermost, tunica serosa enveloped the entire organ and increased in thickness gradually. The middle, tunica muscularis consisted of an outer circular and inner longitudinal layer of smooth muscle fibres with blood vessels in between. The innermost, tunica mucosa consisted of pseudostratified lining epithelium and lamina propria filled with follicles. The epithelium was distinguished into follicle associated epithelium and interfollicular epithelium. Each follicle consisted of a cortex and medulla separated by a layer of epithelial cells with distinct basement membrane in birds of all ages. Lymphoblast, lymphocytes and macrophages formed the cellular component of the follicle. The number, size and cellular details of lymphoid follicles attained their peak – values by about 58 to 65 days of post hatch period. The interfollicular and subepithelial connective tissue was made up of collagen and reticular fibres with a few elastic fibres. The cellular component in it included plasma cells, eosinophils, mast cells, macrophages and fat cells. Involutory changes in the bursa were recorded from 95 – days post hatch characterised by degeneration of plical epithelium and follicular atrophy. Prominent microscopic features of involution were evident from 140 days of age. The bursa showed follicular degeneration, fibrosis of subepithelialstroma, collapse of plicae, depletion of lymphocytes and fatty replacement of the organ. The lining epithelial cells of bursal mucosa revealed positive reaction to Schiff’s reagent and metachromasia in birds of all ages. Intense acid phosphatase and moderate alkaline phosphatase activity was noticed in the epithelial cells of the bursa, in all the birds. The maximum positive immunoperoxidase activity seen by about 35 to 58 days of age suggested that immunologically the bursa was at its peak functional activity at this age.