The interaction between the effects of food restriction and cold stress on the development of body temperature, homeothermy index, metabolic rate and body weight were studied in Muscovy ducklings from hatching to 21 d of age. 2. The control group (ad libitum fed) and the food restricted group (fed to zero growth rate for 9 d) both became homeothermic when they were 2 d old with moderate (10 degrees C) cold stress. At severe cold stress (0 degrees C) the control group was homeothermic 5 days after hatching. However the food restricted group did not reach homeothermy at 0 degrees C and showed a large decrease (to hatching level) in homeothermy index at 10 degrees C and 0 degrees C after 9 d of food restriction. 3. Body temperature was lower in the food-restricted group during restriction and increased by 1 degree C after 24 h of ad libitum feeding. During food restriction, resting metabolic rate did not increase with age and was lower than the basal and existence metabolic rate predicted by Aschoff and Pohl (1970) and Kendeigh (1970) respectively. 4. The ratio of metabolisable energy (ME) intake to resting metabolic rate was 3 times lower in the food-restricted group than in the control group (0.09 and 0.27 respectively) on day 9. The availability of ME was more important than age for the development of thermoregulation in Muscovy ducklings. It is concluded that small improvements in the feeding regimen of young ducklings enhance the endurance and consequently reduce mortality from to environmental cold stress in a scavenger poultry system.
