The Relation of Fetal Age to the Character of Lesions in Fetal Lambs Infected with Brucella ovis

Cultures of Brucella ovis were inoculated into the conceptus of ewes at various stages of gestation, and the fetal lambs were recovered from 10 to 81 days later. All lambs, the youngest of which was recovered on the 54th day of gestation, had lesions. The character of the lesions varied from that of reticuloendothelial hyperplasia and granulomatous inflammation in fetuses up to 91 days of gestation to that of a lymphoreticular nature with well-formed nodules of reticuloendothelial cells, lymphocytes, and plasma cells in older fetal lambs. It was suggested that the variation in the inflammatory response was attributable to the immaturity of the fetal immunologic system.