Behavioral and Physiologic Effects of Dirty Bedding Exposure in Female ICR Mice.

Exposure of sentinel mice to dirty bedding is commonly used in health monitoring programs to screen colonies for clinical and subclinical disease. Despite the potential stressors present in dirty bedding, including but not limited to microorganisms, pheromones, and ammonia, it is unknown whether sentinel mice exposed to soiled bedding experience stress. In this study, select behavioral and physiologic changes associated with stress were assessed in female ICR mice exposed to dirty bedding. Behavioral parameters included evaluation in the home cage and selected behavioral tests; physiologic measurements included neutrophil:lymphocyte ratio and weight. Mice in the acute group were exposed for 24 h whereas mice in the chronic group were exposed for 4 wk. Mice in the chronic group exposed to dirty bedding weighed less at days 21 and 28 than did control mice. Chronic mice exposed to dirty bedding also exhibited decreased net weight gain over the entire study period as compared with control mice. No significant differences were detected in the other behavioral and physiologic parameters measured. These results indicate that dirty bedding exposure may affect sentinel mice, but further investigation is needed to determine the specific mechanism(s) behind the weight difference.

Effects of Repeated Intraperitoneal Injection of Pharmaceutical-grade and Nonpharmaceutical-grade Corn Oil in Female C57BL/6J Mice.

Due to potential adverse effects on animal wellbeing, the use of nonpharmaceutical-grade substances in animal research must be scientifically justified in cases where a pharmaceutical-grade version of the substance exists. This requirement applies to all substances, including vehicles used to solubilize experimental drugs. To date, no studies have evaluated the direct effect of the pharmaceutical classification of a compound on animal wellbeing. In this study, we evaluated intraperitoneal administration of pharmaceutical-grade corn oil, nonpharmaceutical-grade corn oil, and saline in female C57BL/6J mice. Compounds were administered every 48 h for a total of 4 injections. Mice were evaluated clinically by using body weight, body condition score, visual assessment score, CBC, and serum chemistries. Animals were euthanized at 24 h and 14 d after the final injection. Inflammation of the peritoneal wall and mesenteric fat was assessed microscopically by using a semiquantitative scoring system. Saline-dosed groups had lower pathology scores at both time points. At day 21, pharmaceutical-grade corn oil had a significantly higher pathology score compared with nonpharmaceutical-grade corn oil. No other significant differences between the corn oil groups were observed. The use of nonpharmaceutical grade corn oil did not result in adverse clinical consequences and is presumed safe to use for intraperitoneal injection in mice. Differences in inflammation between the 2 groups suggest that the use of either pharmaceutical-grade or nonpharmaceutical-grade corn oil should be consistent within a study.