Failure to induce defecation in rats exposed to fixed-time schedules of liquid food delivery

Previous studies have found that defecation increases in rats exposed to fixed-time schedules of dry food delivery. The purpose of the present study was to examine whether increases in defecation could be induced in rats exposed to fixed-time schedules of liquid food delivery. Eight rats were exposed to fixed-time 30-, 60-, and 120-s schedules of liquid food delivery. None of the subjects excreted significantly more fecal boli under the fixed-time schedules than during massed-food control sessions in which an equivalent amount of food was presented at the beginning of the sessions. Thus, the present findings identify a previously unknown constraint on schedule-induced defecation in rats.