Effects of price and pellet type on food waste in mice

When laboratory mice are provided with free access to food, they often fragment their food such that it collects on the cage floor - wasted. An operant analysis of food waste, however, has not yet been conducted. The purpose of the present study was to evaluate the effect of response requirement and pellet type on food waste using a behavioral economic paradigm. Sixteen mice responded under a series of escalating fixed ratio schedules. Nose pokes were reinforced with either a grain-based pellet or a fiber-based pellet (diluted with non-digestible cellulose) across conditions. We found that mice spilled a greater percent of the total earned pellets at low response requirements. Additionally, mice spilled more fiber-based pellets relative to grain-based pellets. This difference was most pronounced when the fixed ratio requirement was low and was attenuated as the fixed ratio was increased, and this decrease in food waste across prices was well accounted for by an exponential model. Mice may have been extracting the calorically dense components of the fiber-based pellets only when the schedule of reinforcement was rich. When the schedule of reinforcement was lean, responding for a new pellet likely was a more functional behavior than fragmenting a pellet and discarding portions.