Voluntary Wheel Running as an Effective Intervention in the Management of Excessive Food Usage in CD-1 Mice (Mus musculus)

Some mice demonstrate excessive food-grinding behaviors in which food pellets are broken down into crumbs (orts). This is considered abnormal behavior and is undesirable in a research environment, as it is thought to potentially be a stereotypic behavior suggestive of a negative welfare state in these animals. Further, food grinding often necessitates more frequent food and bedding changes. Research outcomes may also be affected if investigators do not exclude food losses due to grinding when measuring food consumption. We hypothesized some mice may excessively grind food in part to expend energy and access to a running wheel would contribute to a reduction in food grinding. Total daily food usage (the combined weight of food consumption and ort production) was measured for 40 d in CD-1 mice that exhibited food grinding. Median daily food usage was compared 10 d before, 20 d during, and 10 d after access to a running wheel. Additional cages of similar food-grinding mice that did not have access to a running wheel were monitored during the same period for comparison. A significant reduction in food usage was observed in 8 out of the 20 d in which mice had access to a running wheel compared with controls (<i>P</i> < 0.05). This reduction was significantly less than the median daily food usage before and after the running wheels were available (<i>P</i> < 0.01). Food usage significantly increased sharply in the 3 d following removal of the running wheel compared with controls during the same period (<i>P</i> < 0.05). A positive correlation between relative humidity and median daily food usage was observed (<i>P</i> < 0.05). Despite fluctuations in relative humidity, providing a running wheel effectively reduced excessive food-grinding behavior.