Weight and histological studies of growth and regression in the bursa of Fabricius in the mallard, Anas platyrhynchos

Abstract

A weight and histological study of growth and regression of the bursa of Fabricius in captive and wild mallards was made between May 1967 and May 1968. Mean bursal weight reached a maximum by 8 weeks in males and 6 weeks in females, and decreased steadily after 12 weeks in males and 16 weeks in females. During growth of the bursa there was a general enlargement of the bursal follicles, but the trabeculae between the follicles remained thin. During bursal regression the follicular size decreased, and trabeculae thickened. Ultimately the follicles and bursal lumen disappeared leaving connective tissue and blood vessels. A classification was erected to describe the phases of bursal growth and regression.