Characteristics of blood in the pouch young of a marsupial, Setonix brachyurus

Abstract

Blood samples were collected from nine prenatal embryos, aged 16-23 days, and 89 pouch young, aged 1-200 days, of S. brachyurus. Where possible, the following determinations were performed on each sample: total erythrocyte and leucocyte counts, percentage haematocrit, differential counts, and haemoglobin concentration. At birth nearly all cells in blood were nucleated eosinophil megaloblasts but subsequently these were replaced by erythroblasts and erythrocytes, so that in pouch young aged 25 days the majority of the red blood cells were erythrocytes. The site of erythropoiesis changed during embryonic and pouch development of young; it occurred in the yolk sac before birth, then in the liver from day 2 to day 100, in the spleen from day 8 to day 200, and from day 10 in the bone marrow, which was the chief site in adults. In the neonatal quokka the total erythrocyte count was 900,000 cells per 1 mm3, the haematocrit was 20-30%, and the haemoglobin concentration was 5 g per 100 ml. In adults the mean total erythrocyte count was 6-7 x 10*6 cells per 1 mm3, the haematocrit was 42%, and the haemoglobin concentration was 13 g per 100 ml. The liver was the first organ to form granulocytes in the newborn; the adult total blood leucocyte count of 11,000 cells per 1 mm3 was reached at 45 days old. The embryonic nature of the haematopoietic tissue in neonatal marsupials is discussed in relation to the development of immunity.