Behavioral or nutritional drive: which motivation affects rates of food grinding in CD1 mice?

Wire mouse feeders used in laboratory mouse cages typically hold enough food to feed 5 mice for two weeks. However, some mice gnaw the food provided into powder, which they do not ingest. The ground-up food fills the cage, resulting in miscalculations of food consumption, welfare issues with blocked water valves and frequent cage handling, more frequent cage changes, and economic issues of food wastage. There is a dearth of studies attempting to understand the causes behind food grinding behavior. This study, following on from previous work, sought to determine if the motivations behind food grinding were related to a mouse's innate behavioral drive to gnaw or rather a nutritional drive to seek out macronutrient components in the feed. We replicated previous results where high fat treatments (either shell-on sunflower seeds or a diet with macronutrient equivalence to a sunflower kernel), but not the method of delivery of the higher-fat treatments, decreased the amount of ground food produced per cage. Further, the composition of the gnawed food changed over the course of the study, generally with protein increasing and fat decreasing in the gnawed feed, especially after treatments were removed. We also replicated previous results which found differences in the composition of the gnawed feed in comparison to the original diet. These results support the hypothesis that food grinding behavior is driven by a nutritional motivation, not a behavioral one.