Size of Bursa of Fabricius Compared with Ossification of Skull and Maturity of Gonads

Abstract

The bursa of Fabricius, a dorsal diverticulum of the lower intestine, is usually present in young birds and absent in adults. Recently this structure has attracted attention as a means of determining the age of individuals. The conventional criteria for establishing the age of birds are the degree of ossification of the skull, the condition of the gonads, and the plumage, but the simultaneous use of several structures should permit a more accurate determination of the age of an individual bird. It is the aim of this paper to compare the maturity of the bursa of Fabricius with the maturity of the skull and of the gonads. Plumage, a fourth character useful in determining age, is not considered here. The accurate determination of the age of individual birds is of considerable importance in game management, as has been explained by Leopold (1933), Gower (1939), and Petrides (1942); and several investigations have been organized to determine exactly the size of the bursa of game birds (Hochbaum, 1942; Linduska, 1943; Kirkpatrick, 1944). The age of wild birds now is assuming importance in relation to human diseases which are primarily avian or mammalian, because the interpretation of tests for antibodies in wild birds requires a knowledge of the age of the individual bird. The presence of antibodies in young birds means that the etiologic agent is temporally near, while their presence in adults and absence in young birds means that the agent is no longer present. Enzootiologic investigations of this type are in their infancy. The bursa of Fabricius is a lymphoepithelial organ, presumably the site of production of blood elements, and lies dorsally above the cloaca. At least in some species it has an opening exteriorly, reaches it maximum size when the bird is 4-6 months old, and then begins involution. Linduska (1943) and Kirkpatrick (1944) have developed methods of measuring the size of the bursa in live pheasants by insertion of a thin glass rod. Obviously the investigation of the relation of the size of the bursa of Fabricius to the age of the bird can best be made with birds of known ages, as has been done for some species (Riddle, 1928; Kirkpatrick, 1944). However, because of the time and expense of raising and studying the birds, such detailed investigations can be accomplished only 1 The investigations on which this article is based were made with the support and under the auspices of the Yellow Fever Research Service maintained jointly by the Ministry of Education and Health of Brazil and the International Health Division of The Rockefeller Foundation.