How closely do circulating blood glucose levels reflect feeding state in fowls?

1. Amounts of food eaten in 30 min, by fasted-refed immature hens, were not correlated with plasma glucose levels before feeding, or with increases in glucose after feeding. 2. When previously fasted birds were given 0, 5, 10, 15 or 20 g food to eat, their plasma glucose increased by similar amounts with 10, 15 and 20 g, by slightly less with 5 g, and hardly at all with 0 g. 3. When food was removed from free-feeding birds, their plasma glucose levels declined slightly in 2 hr and then remained steady. They declined markedly further overnight, but recovered to a level higher than before deprivation when 10 g food was provided. 4. Four hours darkness during normal daytime had no effect on plasma glucose in fasted-refed birds, but sight of food and presentation of an empty food pan caused slight increases in glucose in 24-hr fasted birds. 5. It is concluded that blood glucose in fowls fluctuates around several "typical" levels, but that there is also much variation between and within birds. Direct (absorbed) and indirect (thermogenic) consequences of feeding probably both contribute to fluctuations in glucose, and these seem more likely to influence regulation of food intake in the longer-term rather than the short-term.