1. An open-circuit, automated, multi-calorimeter system for studies on the energy metabolism of the fowl is described. 2. Discontinuous observations of 10-min duration once each hour for 22 h gave good agreement with continuous observations throughout 22 h. 3. It is essential to train each hen before a series of calorimeter experiments. 4. A distinctive pattern of light-entrained, diurnal variation of metabolic rate has been observed in starving and fed birds of two laying strains.

The energy metabolism of mature male turkeys (Meleagris gallopavo) was determined in a computer-controlled indirect multi-calorimeter system of which the design and operation are described. Daily heat production did not change significantly during an initial 6-d period in the calorimeter chambers. Food intake was at first sufficient to promote a rate of energy retention significantly greater than zero, but decreased to give negative energy retention on day 6; mean energy retention for the whole 6-day period was significantly greater than zero. Heat production was affected little by fasting for 72 h, although the respiratory quotient decreased to 0.72 within 48 h; the heat increment of feeding was therefore small (about 5% of metabolisable energy). Fasting heat production, scaled on metabolic body size (bodyweight in kg)0.75, was similar to that of mature male domestic fowl (Gallus domesticus). Heat production after refeeding was similar to that recorded during the 6 d before fasting. There was a pronounced circadian rhythmicity of heat production in both fed and fasted birds.

1. A technique has been developed for the study of embryonic heart rate during the last week of incubation in a population of 84 embryos. 2. Heart rate is characteristic for a particular embryo but there are clear differences between individuals. 3. The population mean heart rate decreased from 262 beats/min at 14 d to a minimum of 250 beats/min at 19-5 d and then increased rapidly to more than 270 beats/min before hatching. 4. This pattern was repeatable and independent of the flock age. 5. Embryonic heart rate was also independent of egg size and hatching time. 6. The heart rate of male embryos was one to two beats/min lower than that of females.