Effects of caloric manipulations on food intake in baboons

Food intake of seven adult male baboons (Papio cynocephalus anubis) was monitored during daily 22-h experimental sessions. Food was available under a two-component operant schedule. Following completion of the first "procurement component" response requirement, access to food, i.e. a meal, became available under the second "consumption component," during which each response produced a 1-g food pellet. After a 10-min interval in which no response occurred, the consumption component was terminated. The effects of caloric preloads on food intake were determined by giving each baboon a meal of preferred foods 45-60 min prior to the start of the daily session. Caloric preloads decreased food intake during the first 8 h of the session, but had no effect on intake during the entire session. The effects of acute deprivation on food intake were determined by terminating sessions after a baboon had consumed 20-80% of baseline intake, and by starting a session 4-12 h late. Deprivation did not increase subsequent food intake. The effects of the availability of an alternative source of calories on total daily intake were determined by providing access to a dextrose solution. Baboons decreased intake of solid food in accordance with the caloric intake from the dextrose solutions by decreasing the number of meals. Finally, the effects of providing a diet of higher caloric density on food intake were determined. Two of the four baboons tested in this procedure maintained baseline levels of daily caloric intake, while the other two baboons increased daily caloric intake. In summary, free-feeding baboons were relatively insensitive to acute changes in feeding conditions, but were sensitive to long-term changes in the caloric content of available foods.