Fasting heat production of birds Nos1,2 and 3 was 71, 72 and 71 Kcal/kg day respectively, or 67, 78 and 72 if expressed on a kg basis, when measured on the first day of the experiment and fasted for 24-28 hr Net availability (%) of metabolized energy (M.E.), defined as the increase in heat production above fasting during days 2-5 of the experimental period, was 70, 70 and 61 for birds No1,2 and 3 respectively.