RESPIRATORY QUOTIENT AND EMBRYOLOGICAL DEVELOPMENT OF METABOLIC HEAT-PRODUCTION IN THE RHEA (RHEA-AMERICANA)

1. Rheas (Rhea americana) show a typical embryonic course of heat prod uction with a plateau phase between days 27 and 39 (total incubation t ime 38-42 d). 2. In the plateau phase mean oxygen consumption is about 90 mi h(-1) (range 87-108) or 0.17 ml (g h)(-1) (range 0.164-0.211). The total sum of energy consumed is 1.25 kJ g(-1) or 721 kJ per entire egg. This equals 23.3% of the total energy content of the egg. 3. The mean RQ is constant over the whole incubation period at 0.75 (metabol ism fuelled mainly by lipids: 87.3%). 4. Only about 22% of the egg's i nitial yolk dry mass is metabolised during embryogeny. In 3-day-old rh eas the yolk content is still about 30% of juvenile mass. 5. The egg p roperties are in the normal range for precocial birds. (C) 1997 Elsevi er Science Ltd.