Factors affecting the voluntary intake of food by sheep. 1. The role of distension, flow-rate of digesta and propulsive motility in the intestines.

1. Twelve sheep fitted with abomasal cannulas were given ad lib. access to a diet of chopped lucerne (Medicago sativa) hay to a ascertain if the amount of digesta being transported by the intestines was limiting intake. If this was the situation, pumping a solution of the bulk-laxative methylcellulose (100 g/kg; MC) into the abomasum should have reduced intake in proportion to the mass of digesta attributable to the MC and associated water. In preliminary experiments faecal water and wet matter outputs increased by 6.2 and 7.4 g/g MC powder respectively. 2. The infusion of 2.95 kg MC/d did not affect food intake even though wet faecal output increased from a control value of 2.436 to 4.616 kg/d. The transit time of 51 Cr-EDTA through the intestines decreased only slightly during the infusion indicating that MC produced a marked increase in the mass of intestinal contents. Increasing the rate of infusion to 5.336 kg/d increased wet faecal output to 5.437 kg/d, did not change transit time but significantly decreased food intake presumably to protect the intestines from overdistension. After stopping the infusion, food intakes and faecal outputs returned to control values but transit time remained unchanged. The intake of chopped lucerne hay by sheep was not limited by the capacity of the small and large intestines to transport bulk as intake was maintained even through wet faecal output was doubled and the intestines apparently became markedly distended.