Changes in metabolic rates and blood respiratory characteristics during pouch development of a marsupial, Macropus...

Oxygen levels in the pouch of the tammar wallaby, Macropus eugenii, have been related to the metabolic rate of the young at pouch temperatures and the oxygen transport characteristics of its haemoglobin. Until 100 days of age, pouch young show mass-specific rates of oxygen consumption lower than predicted on the basis of body mass. This contrasts with data presented for laboratory mice. Oxygen levels in the pouch approximate atmospheric levels for the first 20 days and at times approaching pouch evacuation at 200 days. However, levels of around 17-18% occur at about the mid-point of pouch life. The oxygen-haemoglobin equilibrium curve shows a high P50 (up to 50 Torr at 36 degrees C) in the neonate, but after 2-3 weeks of age levels drop to those representative of the adult. Concentrations of 2,3-diphosphoglycerate in early pouch young are higher than in the adult animal and peak at around 30 mumol/g Hb. There is a significant decrease in the concentration of this compound with the age of the young.