Motility Responses to Fasting in the Gastrointestinal Tract of Three Avian Species

Abstract

To better understand responses of the avian gastrointestinal tract to fasting, fifteen domestic fowls (Gallus), two Ring-necked Pheasants (Phasianus), and two Barred Owls (Strix) were implanted with chronic Ag-AgCl electrodes and extended myoelectric recordings were made during different degrees of feeding or fasting. The motility responses are described, especially single, strong, spike potential bursts (SPBs) that rapidly propagated in an orad direction. The best explanation for our observations seems to be that when the food in the lumen of the upper digestive tract of a chicken begins to be exhausted, fed-state activity in the gizzard and duodenum is restimulated for a short period by single orad SPBs that propagate rapidly from the distal ileum. This stimulation presumably results from nutritive material being moved into the duodenum and gizzard. When one SPB becomes insufficient to stimulate upper-tract activity, orad SPBs begin to occur more frequently. Eventually the stronger rhythmic oscillating complex (ROC) occurs when SPBs no longer elicit fed-state activity. The ROC's extended activity presumably moves nutritive material more effectively than single SPBs. After a ROC, fed-state activity in the stomach and duodenum continues for a longer period (30-60 min in birds fasted for 24 hr). Both SPBs and ROCs continue to occur as long as a bird fasts (≥80 hr). Single strong orad SPBs and prolonged ROCs appear to be successive mechanisms whereby, in times of food deprivation, the gut maximizes its nutritive resources by recycling whatever food still remains within the digestive system. This system exists in the two galliforms studied, but apparently not in Barred Owls.