Feed wastage in laboratory mice, also known as chewing or grinding behavior, is problematic for program management and animal welfare. The destruction of pelleted feed without consumption produces a powder accumulation on the cage floor called orts. Ort accumulation disrupts the cage microenvironment and can clog Lixits resulting in flooding. Moreover, added labor adds cost, and cage disruption increases animal stress. Published studies examining the behavior and ways to mitigate it have had inconsistent results, and the cause or causes have not yet been fully identified. The purpose of this study was to identify methods to reduce the development of chewing behavior in laboratory mice. Female Swiss Webster (Tac:SW) mice (n = 144) were randomly assigned to one of 8 groups (12 cages per group) with 2 housing densities (single and pair) and 4 nesting material paradigms. Mice were housed on clean bedding for 8 wk and then soiled bedding for the next 8 wk. Chewing behavior was evaluated by feed weight, cage weight, and feed scores. The addition of a Diamond Twist significantly increased ort production, while nest transfer decreased it but not significantly. Pair housing increased overall orts but not when adjusted for animal number. These results identified potential contributing factors to chewing behavior. However, further research is needed to elucidate the exact causes and solutions.Abstract
Example chewer mouse cage with high ort accumulation mixed with the bedding 2 wk following cage change (group 2, week 16).
Group number assignment designating nesting material and housing density. Control enrichment consisted of 3 Nestlets and a wood chew block.
Cage setup for each group is shown with clean bedding. (A) Groups 1 and 5: Control enrichment (3 Nestlets and a wood chew block). (B) Groups 2 and 6: Control enrichment with an unraveled Diamond Twist. (C) Groups 3 and 7: Control enrichment with nest transferred from the old cage. (D) Groups 4 and 8: Control enrichment with the Diamond Twist and nest transfer.
Study timeline. Measurements (feed weight, cage weight, feed score, and body weight) were performed weekly, and cages were changed every 2 wk.
Feed scoring system (Reproduced with permission from Garcia and colleagues13). (A) Score 1 if greater than or equal to 75% of the plastic portion of the hopper was still full. (B) Score 2 if the plastic portion of the hopper was 50% to 75% full. (C) Score 3 if the hopper was 25% to 50% full. (D) Score 4 if the hopper was 0% to 25% full. (E) Score 5 if the feed remaining was in the bottom wire portion only. Scores were adjusted to 5 when additional feed was provided to hoppers in between planned refill time points at cage change.
Representative group means and standard deviation of feed and cage weight data at weeks 4, 8, 12, and 16. Feed weight (feed consumed plus ort production) was calculated by subtracting the measured weight from the previous week and adding any additional feed provided. Cage weight (ort production plus animal excretions) was calculated by subtracting from the previous week’s measurement. Means for pair groups (5 to 8) are from measured values (not adjusted by dividing by 2 as done for statistical comparison between single and pair groups). The effect of Diamond Twist on ort accumulation was significant in the overall analyses. Representative time points are depicted. (A) Feed weight for groups 1 to 4. (B) Feed weight for groups 5 to 8. (C) Cage weight for groups 1 to 4. (D) Cage weight for groups 5 to 8.
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